Nuclear Science lesson

In general, Nuclear power is the process of using etreme force to split an atom. At which point an enormous ammount of energy is released and able to be harnessed for use. At this time the only thing we know of that can split an atom is Uranium. After being used, Uranium becomes spent, and even more biologically unstable then it was when it started.So, to answer the question: I doubt a Nuclear power locomotive will be possable, or phesable. The Engine would most certainly have to be rather large to accomidate the Atom smashing workings. And a unit would be down for about a month every month while the small spent rods are replaced with new small rods. After which the area it was in would have to be decontaminated because of possable leakage.Any intelligable, pre-thought, questions? Yes, Pre-thought means you can't just say "NO" because you have a warpered perception of how something actually works.-------------

"Darkness, imprisoning me, all that i see, absolute horror, i cannot live, i cannot die, trapped in myself, body my holding cell."

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RE: Nuclear Science lesson:, JohnNetzlof, Sep-29-03, 03:58 PM, (1) RE: Nuclear Science lesson:, plainsman, Sep-29-03, 04:06 PM, (3) RE: Nuclear Science lesson:, JohnNetzlof, Sep-29-03, 05:04 PM, (5) RE: Nuclear Science lesson:, rdamon, Oct-01-03, 11:57 AM, (19) RE: Nuclear Science lesson:, Brad 110, Sep-29-03, 06:53 PM, (6) RE: Nuclear Science lesson:, JonN, Sep-29-03, 11:42 PM, (7) RE: Nuclear Science lesson:, Brad 110, Sep-30-03, 00:04 AM, (8) RE: Nuclear Science lesson:, JonN, Sep-30-03, 00:16 AM, (9) RE: Nuclear Science lesson:, Brad 110, Sep-30-03, 01:24 AM, (11) RE: Nuclear Science lesson:, MikeF, Sep-30-03, 06:09 PM, (15) RE: Nuclear Science lesson:, jtr1962, Sep-30-03, 00:36 AM, (10) RE: Nuclear Science lesson:, Brad 110, Sep-30-03, 01:34 AM, (12) RE: Nuclear Science lesson:, LARKIE, Sep-30-03, 07:01 AM, (13) RE: Nuclear Science lesson:, Brad 110, Sep-30-03, 04:08 PM, (14) RE: Nuclear Science lesson:, MikeF, Sep-30-03, 07:45 PM, (16) RE: Nuclear Science lesson:, JonN, Sep-30-03, 08:39 PM, (17) RE: Nuclear Science lesson:, MikeF, Oct-01-03, 06:28 PM, (20) RE: Nuclear Science lesson:, LARKIE, Oct-01-03, 08:30 AM, (18) RE: Nuclear Science lesson:, MikeF, Oct-01-03, 07:08 PM, (21) RE: Nuclear Science lesson:, Brad 110, Oct-01-03, 10:42 PM, (22) RE: Nuclear Science lesson:, LARKIE, Oct-02-03, 04:25 AM, (23) RE: Nuclear Science lesson:, Brad 110, Oct-02-03, 04:50 PM, (25) RE: Nuclear Science lesson:, MikeF, Oct-02-03, 06:02 PM, (26) RE: Nuclear Science lesson:, Brad 110, Oct-02-03, 10:32 PM, (27) RE: Nuclear Science lesson:, JonN, Oct-02-03, 09:58 AM, (24) RE: Nuclear Science lesson:, BlakeTyner, Oct-03-03, 01:58 AM, (28) RE: Nuclear Science lesson:, LARKIE, Oct-04-03, 10:14 AM, (29) RE: Nuclear Science lesson:, Brad 110, Oct-04-03, 03:39 PM, (30) RE: Nuclear Science lesson:, MikeF, Oct-04-03, 11:30 PM, (31) RE: Nuclear Science lesson:, LARKIE, Oct-06-03, 05:45 AM, (32) RE: Nuclear Science lesson:, MikeF, Oct-06-03, 08:58 PM, (33) RE: Nuclear Science lesson:, chucksc, Oct-06-03, 09:24 PM, (34) RE: Nuclear Science lesson:, NCC1701E, Oct-06-03, 11:27 PM, (35) RE: Nuclear Science lesson:, Brad 110, Oct-07-03, 02:52 PM, (36) RE: Nuclear Science lesson:, chucksc, Oct-07-03, 03:49 PM, (37) RE: Nuclear Science lesson:, JonN, Oct-07-03, 06:36 PM, (39) RE: Nuclear Science lesson:, Brad 110, Oct-08-03, 01:46 AM, (42) RE: Nuclear Science lesson:, NW_611, Oct-07-03, 04:45 PM, (38) RE: Nuclear Science lesson:, jtr1962, Oct-07-03, 09:11 PM, (40) RE: Nuclear Science lesson:, JonN, Oct-07-03, 10:43 PM, (41) RE: Nuclear Science lesson:, Brad 110, Oct-08-03, 02:05 AM, (43)

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LAST EDITED ON Sep-29-03 AT 03:59 PM (EDT)

Now, though, a TINY reactor could take the place of a fire-box and work in a steam loco, but in a "diesel" you would be hard pressed for room for a large enough reactor and the electric convertor/ resistors.-------------

"Darkness, imprisoning me, all that i see, absolute horror, i cannot live, i cannot die, trapped in myself, body my holding cell."

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Not to mention the necessary shielding which would really raise the weight. You can't just have an "ooops it broke" or "we didn't mean to derail, sorry" situation, so would have to be able to withstand any foreseeable calamity.
Bob

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True, but it might ALSO inproove things. Knowing that you HAVE a VERY volatile load on board, one would take more precautionary measures when moving around the trains.-------------

"Darkness, imprisoning me, all that i see, absolute horror, i cannot live, i cannot die, trapped in myself, body my holding cell."

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This reminded me of the NB-36H project in the 1950'shttp://www.ufx.org/nepa/nepa3.htmAs well as some other projects...http://www.nuclear.com/history/Nuclear_airplanes.htmlhttp://www.ufx.org/nepa/nepa.htmCould be a good modification to the "Big Blow" designAlso a good way to light up some of the good railfanning spots at night!!

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LAST EDITED ON Sep-29-03 AT 07:11 PM (EDT)

>In general, Nuclear power is the process of using etreme
>force to split an atom. At which point an enormous ammount
>of energy is released and able to be harnessed for use. At
>this time the only thing we know of that can split an atom
>is Uranium. After being used, Uranium becomes spent, and
>even more biologically unstable then it was when it started.???!?!?In a PWR (pressurised water reactor -- the kind we have been talking about and the bulk of all commerical power reactors) neutrons are used to split Uranium 235 atoms (fission). Each fission releases (on average)about 200 Mev of energy, 2.4 neutrons, and two (sometimes more) large pieces of the former uranium nucleus. 200 Mev is a small amount of enery, but there are "billions and billions" (thank you Carl Sagen) of fissions going on. Far from needing extreme force, the neutrons must be slowed down (lose energy) between the time they are produced from fission and the time they cause the next fission (which is why these sorts of reactors are also called thermal reactors -- they use termalized neutrons). After undergoing fission the Uranium is no longer Uranium and becomes something else (the two pieces mentioned above). Some of these new isotopes are intensley radioactive. Some have long half lives as well. Some are stable and not radioactive. A significant portion of the reactors power (something on the order of 7% IIRC) comes from the decay of fission products.In case anyone is interested, the following is a usenet posting I produced back in January for sci.military.naval:The basic mechanics and math are publicly available and are pretty
much the same as any pressurized water reactor in the public sector.If you know anything about reactors, you know the chain reaction
consists of neutrons hitting Uranium 235 atoms, splitting them,
releasing more neutrons and energy, the new neutrons causing more
fissions, releasing more neutrons, etc., etc. What might be less well
known is that the neutrons from fission cannot, when produced, cause
fission. They, depending on your point of view, either have too high
an energy level or are moving too fast to cause fission. They have to
slow down, losing energy in the process. They do this by colliding
with other atoms (or rather the nuclei of other atoms), giving up
energy with each collision with some thing possessing less energy then
it has. The process is called "moderation" and the slowed down
neutrons are said to be thermalized (which is why PWR's are also
called thermal reactors - they use "thermal" neutrons). It turns out
that the most efficient energy transfer occurs when the neutron
collides with something with the same mass. (All this is straight
Newtonian mechanics, nothing fancy.) This is where water comes in.
Water has lots of hydrogen, and a hydrogen nucleus a proton, is about
the same mass as a neutron. It makes a good moderator. Water, however,
does expand and contract under changes in temp. This affects it
ability as a moderator (less dense water means the neutron has to
travel a longer path to get enough collisions to thermalize) and also
how many neutrons are lost to the fission process (for a variety of
reasons) during the time and distance it takes to thermalize. In
effect, the cooler the water around the core becomes, the more
reactive the core becomes, and the more heat it produces.Since water has good chemical properties and tolerable heat carrying
capacity it does double duty as coolant, as well as moderator, and is
generally called primary or main coolant. It is kept under very high
pressure (several thousand pounds) and does not boil even though it is
kept around 500 degrees when the plant is operating. Hot main coolant
is taken from the top of the reactor vessel (the pressurized "tank"
where the core lives), pumped to the steam generators with special
main coolant pumps, and returned to the bottom of the reactor vessel,
a few degrees cooler, to be reheated. The steam generators are
essentially tube and shell heat exchangers, with the main coolant in
the tubes and feed water on the shell side. The 500-degree tubes boil
the feed water, and the main coolant give up some of its heat in the
process, providing steam to the steam turbines and other steam driven
equipment. The amount of heat transferred in the steam generator can
be measured as a function of the flow rate of the primary coolant, the
specific heat capacity of the liquid (fixed for water), and the
temperature difference between the coolant entering the steam
generator and the coolant leaving the steam generator. It can also be
measured as a function of the area of the tube walls, a factor for
thermal conductivity (the opposite of R factor in insulation), and the
temp difference across the tube wall. Works out the same either way.Told you all that so I could tell you this:Imagine a ship sailing along a two thirds. For our purposes let us
consider all steam loads other then the main engine turbines as
"fixed" and not subject to change. Everything is in equilibrium; the
throttles are open some fixed amount, a steady amount of steam (and
heat energy in the steam) is being bled off from the steam generator,
and there is a steady and constant difference between the hot coolant
entering the steam generators and the and the cooler coolant leaving
the steam generators. (Leave aside, if you will, how we got to this
point -- startup is another subject.) Suppose the Captain rings up
more speed. The throttle man opens the valve and more steam is taken
from the steam generator. That means more heat is being taken out as
well, and that means that the coolant leaving the steam generator will
be cooler then before. When this cooler coolant reaches the core, it
will cause the core to become more reactive, producing more heat,
causing the coolant coming to the steam generators to be a little
warmer. The greater difference in temp between the hot and cold side
is the measure of the extra energy provided to meet the increased
steam demand. Same thing in reverse if we slow down. The valve is
closed further, less steam taken from the SG's, the coolant cool side
temp rises (less heat being transferred), causing the reactor to be
come less reactive (coolant less dense), causing the hot side coolant
temp to fall, again, the amount of main coolant tem change on both hot
and cold sides equaling the change in steam demand. Simple. One man,
one valve, controls the whole plant. Reactor power always follows
steam demand.What, one may be tempted to ask, do the control rods control then, if
not reactor power? The answer is, reactor temperature. The reactor
core is sort of like a wick in a kerosene lamp, burning only at one
end. The rods act like the wick guard, controlling how much of the
core will be exposed to fission. Steam demand will control how fast
that portion is consumed. When I said the main coolant is at 500
degrees, that number is the hot side temp plus the cold side temp, the
quantity divided by two. It is known as T(ave). As the exposed section
of the core is consumed, both the hot leg and cold leg temps will
drop, but the temp difference between them will remain the same (that,
remember, is a function of steam demand). Because the reactor is
designed to be operated in a certain temperature range, "the green
band", as T(ave) drifts down during operation, the reactor operator
will shim the rods out a tad, exposing more of the core, and causing
t(ave) to rise.It is so elegantly simple that it seems a bloody shame it is so
potentially hazardous.Brad Meyer

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LAST EDITED ON Sep-29-03 AT 11:48 PM (EDT)

From an engineering standpoint, I think them main problem would be finding a way to cool the reactor, as the reactor vessel and it's shielding could probably be made to fit. Also, the big steam turbine could be a problem. Take a look at this cutaway of a 688i SSNAs you can see, the reactor compartment (containing the reactor vessel and all it's cooling gear) only occupies a 25 foot long hull section, but the main machinery/turbines occupy nearly 4 times that.
This also highlights the low thermal efficiency of nuclear reactors: the reactor on a 688 is rated at 190Mw, but the power output at the propellor is only 30,000Hp (22.4Mw), meaning that you would would need a 20Mw reactor to get the same power at the wheels as an SD40-2 ( I think a 20Mw reactor could fit on a loco, as the horizontal size limit would be 4 feet, which I think a reactor of that power could fit into)About cooling: Nuc subs reduce the temperature of the main coolant by running the pipe of the coolant "loop" directly through a tank of cycled seawater. Shorefront commercial reactors can employ this principle as well, but inland reactors must have massive cooling towers, using air to reduce the temperature of the coolant. I dont see how the coolant could be cooled effectivly on a vehicle like a locomotive... The cooling system would be just too large to fit most RR size restrictions.
Bottom line: it is still practily impossible to build a nuclear locomotive, given the size requirements of the cooling system. You could fit a reactor, but you would quickly melt it down without the oversize cooling system.Jonathan Nikiforovs.
Milepost 180, CP Belleville Sub.Repainter for Yonder Locomotive Works.

"A crictic is a man who creates nothing and thereby feels qualified to judge the work of creative men. There is logic in this; he is unbiased - he hates all creative people equally." - Lazarus Long

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>From an engineering standpoint, I think them main problem
>would be finding a way to cool the reactor . . .Minor consideration. Power (and heat) follows steam demand.>This also highlights the low thermal efficiency of nuclear
>reactors: the reactor on a 688 is rated at 190Mw, but the
>power output at the propellor is only 30,000Hp (22.4Mw),
>meaning that you would would need a 20Mw reactor to get the
>same power at the wheels as an SD40-2 ( I think a 20Mw
>reactor could fit on a loco, as the horizontal size limit
>would be 4 feet, which I think a reactor of that power could
>fit into) No, this means that only that much power goes to the shaft. The Rx also runs the hotel loads (heat, light, laundry, food prep, distillation of fresh water, etc., etc.>About cooling: Nuc subs reduce the temperature of the main
>coolant by running the pipe of the coolant "loop" directly
>through a tank of cycled seawater. No such thing. Cool down is started by using the steam generators to remove heat, and continued through the RPFW coolers. Primary plant piping does not touch salt water at any point in the cycle.>Shorefront commercial
>reactors can employ this principle as well, but inland
>reactors must have massive cooling towers, using air to
>reduce the temperature of the coolant. This is to cool the condensate in the secondary plant, not the primary coolant. Primary coolant is cooled by using it to produce steam in the secondary plant.>I dont see how the
>coolant could be cooled effectivly on a vehicle like a
>locomotive... The cooling system would be just too large to
>fit most RR size restrictions. Given that power follows steam demand, there is no reason to cool the primary plant except maintenance, which means that cooling could be done via external hookup at the maintenance site.>Bottom line: it is still practily impossible to build a
>nuclear locomotive . . .No, there is just no economic bennefit to doing so.
Brad Meyer

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LAST EDITED ON Sep-30-03 AT 00:17 AM (EDT)

Well, you're the expert...
I stand corrected now.Jonathan Nikiforovs.
Milepost 180, CP Belleville Sub.Repainter for Yonder Locomotive Works.

"A crictic is a man who creates nothing and thereby feels qualified to judge the work of creative men. There is logic in this; he is unbiased - he hates all creative people equally." - Lazarus Long

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Well, the KOG (kindly old gentleman, AKA Admiral Rickover) set up a training system that sort of beat that kind of info into your head so that it never ever fully leaves you. Anyone who made it through the classrom phase of Naval Nuclear Power Training during his time on watch would probably agree.Brad Meyer

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>>From an engineering standpoint, I think them main problem
>>would be finding a way to cool the reactor . . .
>
>Minor consideration. Power (and heat) follows steam demand. I liked your write-up, but I think you're missing his point. If you want 20Mw out the turbine shaft, you need to dump at *least* 40MW out the 'main condenser'. In a sub, this is easy. But you would need a pretty massive air-cooled condenser to get rid of this much power.>
>>This also highlights the low thermal efficiency of nuclear
>>reactors: the reactor on a 688 is rated at 190Mw, but the
>>power output at the propellor is only 30,000Hp (22.4Mw),
>>meaning that you would would need a 20Mw reactor to get the
>>same power at the wheels as an SD40-2 ( I think a 20Mw
>>reactor could fit on a loco, as the horizontal size limit
>>would be 4 feet, which I think a reactor of that power could
>>fit into)
>
>No, this means that only that much power goes to the shaft.
>The Rx also runs the hotel loads (heat, light, laundry, food
>prep, distillation of fresh water, etc., etc. Oh come on now, as a former EMC(SS) on some SSN's, I know the 'hotel load' when under way is less than 2MW unless you're in fast-speed pumps, then it is still under 4MW. It isn't that much larger for 'boomer's. And how much you run the evaporator depends on how many 'hollywood' showers you let the crew get away with A good 'rule-of-thumb' was between 5 and 10% power to 'idle' the steam plant with the mains on the jack.>
>>About cooling: Nuc subs reduce the temperature of the main
>>coolant by running the pipe of the coolant "loop" directly
>>through a tank of cycled seawater.
>
>No such thing. He *may* be referring to the XC system on old S5W boats. But it was only for emergencies, so I wouldn't count it either really. I doubt he knows plant in *that* much detail, but it may be something picked up here or there....>Cool down is started by using the steam
>generators to remove heat, and continued through the RPFW
>coolers. Primary plant piping does not touch salt water at
>any point in the cycle. Except in the XC system >
>>I dont see how the
>>coolant could be cooled effectivly on a vehicle like a
>>locomotive... The cooling system would be just too large to
>>fit most RR size restrictions.
>
>Given that power follows steam demand, there is no reason to
>cool the primary plant except maintenance, which means that
>cooling could be done via external hookup at the maintenance
>site.
>Or in an emergency when decay heat must be removed and the normal steam plant is OOS. Remember, decay heat??

Mike F

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>This also highlights the low thermal efficiency of nuclear
>reactors: the reactor on a 688 is rated at 190Mw, but the
>power output at the propellor is only 30,000Hp (22.4Mw),
>meaning that you would would need a 20Mw reactor to get the
>same power at the wheels as an SD40-2 ( I think a 20Mw
>reactor could fit on a loco, as the horizontal size limit
>would be 4 feet, which I think a reactor of that power could
>fit into) One thing to consider is that the power output at the propeller might be dramatically higher than 30,000 HP. I don't think the US Military is in the habit of releasing exact figures for the power or top speed of its warships. Knowing the shape and size, it would be fairly easy to calculate the top speed of a nuclear sub if exact HP figures were released, and for strategic reasons the US Navy would rather not have those top speeds be public knowledge. The usual 30+ knots given for everything leaves alot of latitude. I wouldn't be at all suprised if the power output at the shaft was double the "official figure". Also, is that 30,000 HP in the form of propeller thrust or shaft HP? There is a huge difference as the propeller is far from 100% efficient at converting shaft power into thrust(I think the figure is 75% or less). 30,000 HP in propeller thrust might mean 40,000 shaft HP.>The cooling system would be just too large to
>fit most RR size restrictions.
>Bottom line: it is still practily impossible to build a
>nuclear locomotive, given the size requirements of the
>cooling system. You could fit a reactor, but you would
>quickly melt it down without the oversize cooling system.Let's say you could make the whole cycle 25% efficient. To put out 6000 HP at the wheels would require a thermal output of 24,000 HP, or 17904 KW. The waste heat would be 13428 KW. Dynamic brake grids on an SD90, for example, can dissipate something on the order of 6000 kW so it is certainly possible to engineer an air-cooled system dissipating twice that. The concept is simple-the fluid carrying the waste heat flows through a forced air heat exhanger with many closely spaced fins.Very nice diagram, BTW.

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>One thing to consider is that the power output at the
>propeller might be dramatically higher than 30,000 HP. I
>don't think the US Military is in the habit of releasing
>exact figures for the power or top speed of its warships. The way to back figure it is to look at the rating on the shaft thrust bearing and back figure from there. That would give one at least a thoretical max power that could be applied to the shaft.>Knowing the shape and size, it would be fairly easy to
>calculate the top speed of a nuclear sub if exact HP figures
>were released . . .Actually not, as they do some very clever things with hull coverings to minimize drag (at least on the subs).Brad Meyer

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"Imagine a ship sailing along a two thirds. For our purposes let us
consider all steam loads other then the main engine turbines as
"fixed" and not subject to change. Everything is in equilibrium; the
throttles are open some fixed amount, a steady amount of steam (and
heat energy in the steam) is being bled off from the steam generator,
and there is a steady and constant difference between the hot coolant
entering the steam generators and the and the cooler coolant leaving
the steam generators. (Leave aside, if you will, how we got to this
point -- startup is another subject.) Suppose the Captain rings up
more speed. The throttle man opens the valve and more steam is taken
from the steam generator. That means more heat is being taken out as
well, and that means that the coolant leaving the steam generator will
be cooler then before. When this cooler coolant reaches the core, it
will cause the core to become more reactive, producing more heat,
causing the coolant coming to the steam generators to be a little
warmer. The greater difference in temp between the hot and cold side
is the measure of the extra energy provided to meet the increased
steam demand. Same thing in reverse if we slow down. The valve is
closed further, less steam taken from the SG's, the coolant cool side
temp rises (less heat being transferred), causing the reactor to be
come less reactive (coolant less dense), causing the hot side coolant
temp to fall, again, the amount of main coolant tem change on both hot
and cold sides equaling the change in steam demand. Simple. One man,
one valve, controls the whole plant. Reactor power always follows
steam demand." ---------------------------The above statement,although elegant,is not a realistic description of how a reactor works.It also assumes that a reactor is somehow self regulating,dependant on external actions.
Let's go back to steam boiler basics.A boiler is built to provide steam at a constant pressure and temperature to power a vessel\electric turbine,as in your analogy.
This requires heat,whether supplied by oil firing,or an intermediate fluid transfer medium,such as water or CO2 in nuclear reactors.The temperature doesn't change,only the heat transferred at that constant temperature.
A boiler,by its very construction,IE having a safety valve limits the pressure,and hence the temperature of the steam produced.IE at atmospheric temperature water will only form steam at a temperature of 212F.Similarly at 300PSI the steam temperature is ~417F,and at 1000PSI ~545F.
If you want to heat the steam further,then you have to use "external" superheaters.When more steam is required in a conventional boiler,then more heat is added by turning up the burners,or lighting additional ones,until the heat input balances the heat output,still at the original boiler temperature and pressure.
The flame temperature stays the same too,only there's a bigger volume of flame.IE fuel burned.Merely opening the steam valve,will have the effect of dropping the boiler pressure,(and the steam temperature too),if the firing rate is not altered to evaporate the water faster to keep up with steeam demand.A nuclear reactor,for all its complexity,only replaces the oil burners in the above scenario.Its core temperature is also kept at an optimum temperature,safely below the melting point of its fuel rods,and their containment devices.Thus when the reactor is required to provide more power,more of it's core is exposed for fission to increase,the core itself stays at its optimum temperature,but its heat transfer area increases due to this increase in fissionable volume.The whole purpose of the reactor coolant is to transfer this additional heat away,still at constant temperature conditions,to maintain the stable reactor temperature.This extra heat is then transferred to the steam boiler to maintain its constant pressure temperature production of the increased volume of steam required.(and hence power produced)The primary purpose of control rods is to stop the nuclear reaction,if the primary coolant supply fails,and a happy by product of this is that the reactor can be regulated power wise from 0-100% output.The "one man steam valve" analogy,requires another man firing the boilers,or a control system doing that job,as opening the valve,or closing it,without such backup will either result in loss of pressure or overpressure in the boiler concerned,and not the constant pressure temperature conditions a boiler works under.

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>The above statement,although elegant,is not a realistic
>description of how a reactor works.It is, in fact, a very realistic description.>It also assumes that a
>reactor is somehow self regulating,dependant on external
>actions. Also very true. The negative temperature coefficient of reactivity provides the negative feedback that allows power level to follow steam demand. >Let's go back to steam boiler basics.A boiler is built to
>provide steam at a constant pressure and temperature to
>power a vessel\electric turbine,as in your analogy.
>This requires heat,whether supplied by oil firing,or an
>intermediate fluid transfer medium,such as water or CO2 in
>nuclear reactors. The difference is, that in a conventionally fired plant, heat is added by lighting off more burners. In a PWR plant heat is added by increasing the delta T across the primary side of the steam generator. >The temperature doesn't change,only the heat transferred at
>that constant temperature. The temerature of the steam doesn't change. Same same for a steam generator. The amount of steam produced changes.>A boiler,by its very construction,IE having a safety valve
>limits the pressure,and hence the temperature of the steam
>produced.IE at atmospheric temperature water will only form
>steam at a temperature of 212F.Similarly at 300PSI the steam
>temperature is ~417F,and at 1000PSI ~545F. In a conventionally fired plant, if steam demand increases, and no action is taken, what happens? Boiler temp goes down and steam pressure drops. What to do? Light off more burners. In a PWR plant, the equivilent of lighting off more burners happens automatically -- the primary coolant returning to the core is cooler, causing the core to become more reactive, increasing the heat energy (and temp) carried by the water leaving the core going back to the steam generators, allowing more steam to be produced.>When more steam is required in a conventional boiler,then
>more heat is added by turning up the burners,or lighting
>additional ones,until the heat input balances the heat
>output,still at the original boiler temperature and
>pressure. Same same for the PWR. The only thing that changes is the inleat and outlet temps of the primary coolant circulating through the primary side os the S/G.>The flame temperature stays the same too,only there's a
>bigger volume of flame.IE fuel burned.Flame temp in your example is the equivilent of fuel plate temp in the core, which also stays the same. More fuel is being burned because the core has become more reactive because of the cooler water returning from the steam generator.>Merely opening the steam valve,will have the effect of
>dropping the boiler pressure,(and the steam temperature
>too),if the firing rate is not altered to evaporate the
>water faster to keep up with steeam demand. Exactly. In a conventionally fired plant this is accomplished manually by adjusting the burn rate. In a PWR it is accomplished automatically by sending cooler water back to the core and getting hotter was returned to the S/G. The Tave across the primary side of the S/G doesn't change, but the delat T becomes larger, which means more BTU's are being transfered. Conversely, if the plant goes "hot behind the stops" (i.e. the main steam stops are closed. no heat is being removed from the ppirmary coolant in the S/G so there is no delta T across the S/G and Rx power drops to zero, even though the plant is still critical. (Criticality is a function of the change in neutron population per generation. It is not a measure of how many neurtrons there are or how much power is being produced.)>A nuclear reactor,for all its complexity,only replaces the
>oil burners in the above scenario.Its core temperature is
>also kept at an optimum temperature,safely below the melting
>point of its fuel rods,and their containment devices. Exactly so. Therefore, when it is producing power (heat) the temperature of the water leaving the core is greater then the temperature of the water returning to the core. This delta T is a measure of how much heat is being transfered from the core. The average temp of the core does not change (it will fluctuate during a steam transient, but return to its original value).>Thus when the reactor is required to provide more power,more
>of it's core is exposed for fission to increase . . .No. When more power is required the cooler primary coolant returning to the core causes an increase in the number fissions occuring in the existing exposed fuel. The rods don't control power, they control Tave in the core. The delta T between inlet and outlet controls power.> . . .the core
>itself stays at its optimum temperature . . .Exactly backwards. Tave of the core is the one thing that is manually controlled, and rods are shimmed to "maintain Tave in the green band".>The whole purpose of the reactor coolant is to
>transfer this additional heat away,still at constant
>temperature conditions,to maintain the stable reactor
>temperature. No, that is only part of the purpose. It also serves as the neutron moderator. (In gas cooled and sodium cooled plants this moderation is typically done by graphite.)>The primary purpose of control rods is to stop the nuclear
>reaction . . .No, the primary purpose is to regulate Tave. Stopping the reaction is a secondary purpose.>The "one man steam valve" analogy,requires another man
>firing the boilers,or a control system doing that job . . .Exactly. In this case, the control system is the negative tempature coefficient of reactivity. Cooler water makes the core more reactive, causing more fissions per unit time, resulting in more heat being produced.
Brad Meyer

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<snip> ---------------------------
>
>The above statement,although elegant,is not a realistic
>description of how a reactor works.It also assumes that a
>reactor is somehow self regulating,dependant on external
>actions.
>It is in *fact* precisely how the highly enriched, PWR reactor used in Naval vessels works. Been there, learned it under Rickover, did it, taught others, helped 'birth' the Ohio class. The negative temperature coefficient of such LWR's makes the reactor follow steam demand.In commercial PWR's, it is a bit more complicated, but the reactor follows the steam demand in much the same way. Once on line, the operator 'dials-in' the desired MW load on the turbine-generator. As it draws more (or less) steam, the reactor power follows. Control rods are moved in/out simply to maintain the average temperature at the desired operating point.>
>Let's go back to steam boiler basics.A boiler is built to
>provide steam at a constant pressure and temperature to
>power a vessel\electric turbine,as in your analogy.
>This requires heat,whether supplied by oil firing,or an
>intermediate fluid transfer medium,such as water or CO2 in
>nuclear reactors.
>
>The temperature doesn't change,only the heat transferred at
>that constant temperature. Sorry, you got nuclear reactors wrong.In PWR nucs, the increase steam demand will drop the cold-leg temperature a few degrees. Not much, but enough that the negative reactivity coefficient will begin raising power. This power increase continues until the hot-leg is heat above where it was initially by almost the same amount that the cold-leg cooled. Result is average temperature is the same, cold-leg colder, hot-leg hotter, and total power higher.>A boiler,by its very construction,IE having a safety valve
>limits the pressure,and hence the temperature of the steam
>produced.IE at atmospheric temperature water will only form
>steam at a temperature of 212F.Similarly at 300PSI the steam
>temperature is ~417F,and at 1000PSI ~545F.
>If you want to heat the steam further,then you have to use
>"external" superheaters. Which has nothing to do with how you control the power in a reactor, or the firing rate inside the boiler section.>
>Merely opening the steam valve,will have the effect of
>dropping the boiler pressure,(and the steam temperature
>too),if the firing rate is not altered to evaporate the
>water faster to keep up with steeam demand. In commercial boilers, this is done automatically, in reactors, nuclear physics does it for you automatically.>
>A nuclear reactor,for all its complexity,only replaces the
>oil burners in the above scenario.Its core temperature is
>also kept at an optimum temperature,safely below the melting
>point of its fuel rods,and their containment devices.
>
>Thus when the reactor is required to provide more power,more
>of it's core is exposed for fission to increase,the core
>itself stays at its optimum temperature,but its heat
>transfer area increases due to this increase in fissionable
>volume.The whole purpose of the reactor coolant is to
>transfer this additional heat away,still at constant
>temperature conditions,to maintain the stable reactor
>temperature. You obviously read this out of some high-school text and have never studied or operated a real nuclear plant. Brad's description is right on target (oops, I mean submarine).Having worked in the nuclear field for twenty years, both subs and commercial, I know a bit about the subject. Care to guess how power is controled in a BWR?? By changing core flow.>
>This extra heat is then transferred to the steam boiler to
>maintain its constant pressure temperature production of the
>increased volume of steam required.(and hence power
>produced) And with the primary coolant temperature kept constant, the steam pressure in the steam generators actually *drops* with increasing load. This is because of the larger 'delta-t' across the tube wall from primary coolant to secondary. Some naval plants have steam pressure as high as 550 at standby, and drop down as low as 380 at a full bell (in certain modes).>
>The primary purpose of control rods is to stop the nuclear
>reaction,if the primary coolant supply fails,and a happy by
>product of this is that the reactor can be regulated power
>wise from 0-100% output.
>
>The "one man steam valve" analogy,requires another man
>firing the boilers,or a control system doing that job,as
>opening the valve,or closing it,without such backup will
>either result in loss of pressure or overpressure in the
>boiler concerned,and not the constant pressure temperature
>conditions a boiler works under.
>In fossil boilers, yes. An automated control system. In naval nuclear power program, no. Physics rules. It takes several people standing watch, but most of that is for emergencies, and line-up changes. The RO gets to 'shim' rods once in a while to control temperature, the electric-operator gets bored. Engine-room upper-level is bored to death. Lower-level on some boats gets to have some 'excitement' by lighting off the evaporator once in a while to "make water".Qualified electrical, throttleman, watch-supervisor, and even engineering-officer-of-watch. Fast-attacks had more 'fun' than boomers, and throttleman had very direct control of reactor power.

Mike F

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>Qualified electrical, throttleman, watch-supervisor, and
>even engineering-officer-of-watch. Fast-attacks had more
>'fun' than boomers, and throttleman had very direct control
>of reactor power.Would this have something to do with the fact that the reactor cooling systems on the SSNs use pumps, while the system on the Ohio SSBNs rely on natural convection currents?
Jonathan Nikiforovs.
Milepost 180, CP Belleville Sub.Repainter for Yonder Locomotive Works.

"A crictic is a man who creates nothing and thereby feels qualified to judge the work of creative men. There is logic in this; he is unbiased - he hates all creative people equally." - Lazarus Long

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>>Qualified electrical, throttleman, watch-supervisor, and
>>even engineering-officer-of-watch. Fast-attacks had more
>>'fun' than boomers, and throttleman had very direct control
>>of reactor power.
>
>Would this have something to do with the fact that the
>reactor cooling systems on the SSNs use pumps, while the
>system on the Ohio SSBNs rely on natural convection
>currents? "Can neither confirm nor deny" the use of natural convection. But the Ohio did have a thing called 'low-flow mode'."Emergency pump starts", were always a bit of excitement. After shifting to 'hi-flow mode', limit is shaft RPM and 105% on the reactor (and a temperature limit, but we didn't call it Tave). As one 'four-striper' said to me in manuevering after conducting one on me as EOOW, "Hum, eight decades-per-minute in the power range, not bad Chief!!!"

Mike F

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Sorry,Brad and Mike,I cannot accept that a nuclear reactor,can self regulate,merely by opening the main steam valve.It may self regulate,IE "hunt" about a steady state value of power,say 50%,but it cannot go,by itself from 50% output to 100% output,as a steam valve is opened.You require a control system,be it manual,or automatic,to increase the "firing rate",as in any other steam raising operation.After reaching 100% it may well then "hunt" round that value.The only way to increase power is to increase heat output,and in a reactor that is achieved by adjusting the control rods,allowing more neutrons to cause more fissions,which cause more heat.The primary coolant flow is also adjusted from say,37% of its maximum flow rate at idle conditions,to whatever percentage is required to transfer the extra reactor heat produced by the above,whilst keeping the core temperature at a near constant value.The other way to control steam to a turbine is to run the boiler\reactor at full power at all times,but shunt the excess steam not actually required for propulsion straight to the condensor.This approach avoids boiler thermal stresses,but is wasteful of fuel,although if you have a nuclear reator,who cares?This condenser method is used in the triple expansion paddle steamer that I sometimes drive.http://www.btinternet.com/~Paddlers/PSWaverley/
You run at full speed between ports on all furnaces of the boiler,slow down and stop at a port to drop\pickup passengers,say a five minute stop,but the boiler even on one burner will still produce excess steam.Rather than allowing the safety valves to blow,(you may soak the passengers),or the boiler to shutdown,you dump the extra steam to the condenser.This means,when you set off again,you can get back to full power conditions almost immediately.

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>Sorry,Brad and Mike,I cannot accept that a nuclear
>reactor,can self regulate,merely by opening the main steam
>valve.Whether you can 'accept' it or not, doesn't change any facts.>It may self regulate,IE "hunt" about a steady state
>value of power,say 50%,but it cannot go,by itself from 50%
>output to 100% output,as a steam valve is opened.You require
>a control system,be it manual,or automatic,to increase the
>"firing rate",as in any other steam raising operation.After
>reaching 100% it may well then "hunt" round that value. The 'control system' is nuclear physics. The reactor is designed such that anytime the cold-leg temperature drops, it inserts positive reactivity into the reactor. This doesn't change the power level, it changes the rate-of-change of power. So if initially the rate-of-change is zero (you're operating steady-state), cooling the cold-leg water an additional 3-5 degrees will change the physics inside the reactor so the rate-of-change of power is now a positive number.With a positive rate-of-change, power begins increasing, and will *continue* to increase until something 'turns power' and restores the rate-of-change back to zero. That 'something' is the hot-leg water leaving the reactor getting hotter than before. Now power is stable, but at a higher level. Same core flow, colder cold-leg, hotter hot-leg. Steam-generator pressure is lower because of the delta-t across the tubes from primary to secondary (need larger delta-t to transfer the additional power).Anytime power does *not* match steam demand, the coolant temperature rises/falls and that changes the 'rate-of-change' of power in a manner to drive reactor power towards steam demand.It is actually a *very* stable control situation for naval reactors. Commercial ones are less stable (size of core, amount of coolant and other factors change the dynamics).>
>The only way to increase power is to increase heat
>output,and in a reactor that is achieved by adjusting the
>control rods,allowing more neutrons to cause more
>fissions,which cause more heat. No. There are *many* ways to change the power output of a reactor. Anything that affects the chain reaction of neutrons must be considered. Yes, control rods are one. In a PWR, changing the temperature of the inlet water is another. Even fission-product poisons such as Xenon can change power.In commercial PWR, change concentration of boron-10 in the coolant is another. For BWR's, changing the circulation flow, which affects the proportion of steam and water in the fuel channel is yet another.Abruptly cooling the water entering a reactor has been at the root of several power excursion incidents. Letting the temperature of feed-water supplying the secondary side of the steam generator drop due to loss of de-areating feed tank is a classic. Sudden uncontrolled increase in feed water flow is another.Naval reactors can operate with at least one primary coolant loop isolated. If a 'cold' loop is restored to service in a critical reactor, a prompt criticality can occur. This can cause power excursions exceeding 1000% (a *very* bad day).Certain members of a crew that deliberately overrode the interlocks to prevent this (so-called 'cold water interlocks') were imprisoned even though no significant damage occured. It is a classic 'incident report' that was required reading during Rickover's era.>
>The primary coolant flow is also adjusted from say,37% of
>its maximum flow rate at idle conditions,to whatever
>percentage is required to transfer the extra reactor heat
>produced by the above,whilst keeping the core temperature at
>a near constant value. Coolant flow rate is controlled a variety of ways. Typical sub reactor had only fixed two-speed pumps. Nimitz class carriers (and others) have variable speed 'coolant-turbine-generators' for supplying the reactor coolant pumps. But the same basic rule, 'reactor power follows steam demand' still holds.Flow rate in PWR's doesn't *change* reactor power, but it affects how much power can be generated safely and removed. With slow speed pumps, reactor scram set-points are different than when in fast speed. Variable speed flow systems have 'flow-biased' scram points where the exact power level that will cause a scram are based on how much core flow is.>
>The other way to control steam to a turbine is to run the
>boiler\reactor at full power at all times,but shunt the
>excess steam not actually required for propulsion straight
>to the condensor. Of over seven different naval reactor designs I've worked with, none of them used steam dumps other than shipyard testing. While such 'bypass' valves are used in commercial plants for startup, few have the ability to bypass 100% load.>
>This approach avoids boiler thermal stresses,but is wasteful
>of fuel,although if you have a nuclear reator,who cares?
>The Navy cares. Older naval reactor plants had to be refueled every 5-8 years. This was based on an 'average' power level of something like 15% for boomers, and 27% for fast-attacks. Run the reactor at 100% and you need to refuel more often. Much money, down time. Naval reactors can't be refueled as quickly as commercial plants. Shipyard refueling overhauls take from 1 to 3 years.One of the 'holy grail' goals in naval reactor research has been to design a reactor that can contain enough fuel to last 30-40 years (at average power levels). Then the reactor would never need refueling over the life of the boat. It's been a while since I was in, so I don't know if they've ever achieved this.>This condenser method is used in the triple expansion paddle
>steamer that I sometimes
>drive.http://www.btinternet.com/~Paddlers/PSWaverley/
>You run at full speed between ports on all furnaces of the
>boiler,slow down and stop at a port to drop\pickup
>passengers,say a five minute stop,but the boiler even on one
>burner will still produce excess steam.Rather than allowing
>the safety valves to blow,(you may soak the passengers),or
>the boiler to shutdown,you dump the extra steam to the
>condenser. Simple proves that your fossil fired boiler cannot follow load from idle to full power and back as well as a naval nuc can.One test for Ohio class I was involved in was 'cyclic steam transients'. To validate the design, we repeatedly went from all-stop to ahead-flank and back to all-stop. The instructions were for the throttleman (me) to answer the bells as fast as I could as long as steam-generator water-level remained in the program band. The only problem the primary/reactor had was having to start the backup pressurizer heaters to maintain reactor pressure. Power just followed me as fast as I could move the throttles. (I told you some things were 'fun'

Mike F

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I think that pretty well covers it.Brad Meyer

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Never mind lads,despite your continued assertions that you are correct in your "steam valve" nuclear reactor output theory,I shall rest easy with the correct thermodynamic explanation that it is the control rod variable settings that primarily governs the reactors power output,if steam demand changes.IE like turning up(down) the gas on a domestic cooker,as British Energy,http://www.british-energy.com/education/factfiles/index.html
the company that runs all British reactors,so succinctly puts it.PS.The "throttleman" of any vessel shouldn't notice an appreciable difference in the steam conditions,whilst manoeuvering,as that is the job of the boiler\nuclear room staff\controls to keep constant.After all it is easy for the watchkeeper on the bridge to say "Look,I can control the whole 100,000SHP of this containership,by only moving this joystick",The rest after that is control engineering.

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LAST EDITED ON Oct-02-03 AT 04:52 PM (EDT)

For my part, you are free to clutch your ignorance as tightly as suits you. The rods are moved as the article suggests, to maintain the average temperature of the primary coolant. You've had two people who have actually worked in the industry take significant time and effort to explain how a PWR works. I feel quite certain that Cal R, (also a former nuke) should he even be reading this thread, would concur in our explaination. Believe as you will.Brad Meyer

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>Never mind lads,despite your continued assertions that you
>are correct in your "steam valve" nuclear reactor output
>theory,I shall rest easy with the correct thermodynamic
>explanation that it is the control rod variable settings
>that primarily governs the reactors power output,if steam
>demand changes.
>Then you are the fool for not learning something. A couple of us have been operating nuclear reactors for >20 years. I think we know a little more about it than the pablum handed out by a PR web page like the one you read.And as for as thermodynamic theory goes, try again. The control of the reactor is nuclear physics. The process controls of the control rods on a submarine are *manual*.>
>After all it is easy for the watchkeeper on the bridge to
>say "Look,I can control the whole 100,000SHP of this
>containership,by only moving this joystick",The rest after
>that is control engineering. And if you knew where the throttleman stood watch on a naval nuclear submarine, you would know he is within arms reach of the reactor operator (the one who moves the control rods). And I *have* spun the actual steam valves open and shut, watched the RO do *nothing* and the reactor power meter follow my every change in steam demand.But if you don't believe someone who's actually done it, that's your perogotive. Remain ignorant if you like.

Mike F

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>And if you knew where the throttleman stood watch on a naval
>nuclear submarine, you would know he is within arms reach of
>the reactor operator (the one who moves the control rods). Same same for targets as well. RO, MO (throttleman), and EO in that order, with the EOOW behind them. The only thing in secondary plant control is the ships service switchboard. I've been on Longbeach, Truxton, Tuna-prise, Nimitz, and Eisenhower -- all the same in that respect.Brad "nuke target sailor" Meyer

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LAST EDITED ON Oct-02-03 AT 09:59 AM (EDT)

>One of the 'holy grail' goals in naval reactor research has
>been to design a reactor that can contain enough fuel to
>last 30-40 years (at average power levels). Then the
>reactor would never need refueling over the life of the
>boat. It's been a while since I was in, so I don't know if
>they've ever achieved this.I remember reading somewhere that the S9G reactor installed on the new 774 (Virginia) class SSN's are designed to accomplish this.Later tonight I'll see if I can find the article. Jonathan Nikiforovs.
Milepost 180, CP Belleville Sub.Repainter for Yonder Locomotive Works.

"A crictic is a man who creates nothing and thereby feels qualified to judge the work of creative men. There is logic in this; he is unbiased - he hates all creative people equally." - Lazarus Long

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While I don't have first-hand experience with nuclear reactors, I took a very interesting physics class at Commanche Peak Nuclear Power Plant near Glen Rose, TX and the facts are exactly as they were laid out earlier in this thread. I have a buddy who serves on a SSN and this has gotten me interested enough in nuclear subs to have a talk with him about it. But the facts remain the facts, and the guys with the experience are right on the money.Blake Harris
Engineer/fireman, Jefferson and Cypress Bayou Railroad

Vice Dean, Limbaugh Institute for Advanced Conservative Studies

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After pondering the subject some more,I am still not convinced on this steam valve theory,although I can see that it could logically self regulate,by that fashion for each power stage.IE D.slow,slow,half,full,once the main control rods are adjusted to the settings for each output.There's a sparcity of sites to trace such things,classification etc,with pictures of the control stands on a nuclear submarine museum site,having their dials transposed,along with false guages.This they admit to openly as anti espionage measures.However control systems being what they are,I'm sure a reactor can follow load quite happily,with the minimum of human intervention,apart for the sake of emergency action.As PWR's have this amazing ability to self regulate,or is it only submarine reactors?,I would have thought that this feature would be on top of any list of rebuttal statements against those opposed to nuclear power.Again a big silence.I have found a site that deals with reactor controls for marine reactors, http://wwwsoc.nii.ac.jp/aesj/publication/JNST2001/NO.7/38_557-570.pdfand it states quite clearly,on page one,that the primary reactor control for manoeuvering the vessel is the control rods,and obviating the need for chemical shims.I assume the shimming mentioned previously onboard submarines is of this variety,and not brass.Therefore,once again,until I see actual documentary evidence of the steam valve theory,rather than anecdotal evidence,I'll stick with my perception of reactor control.

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>As PWR's have this amazing ability to self regulate,or is it
>only submarine reactors?Pretty much any reactor that uses water as a moderator will show this effect. It is inherent with the fat that water changes density inversly with temperature. The less dense (i.e. hotter)the water, the less efficiently it thermalizes neutrons and the less reactive the core is.>I would have thought that this
>feature would be on top of any list of rebuttal statements
>against those opposed to nuclear power.Again a big silence. Look at your own case. If we grant you no worse then average intellegence and average education, it seems to follow that the average joe one the street isn't going to be swayed by arguments about temperature coefficient for reactivity. There are few people, in my experience, who want to know anything bad enough to do the math and see for themselves. Much easier to just believe.Brad Meyer

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Sorry for boring the rest of the group with all this off-topic posts,
>After pondering the subject some more,I am still not
>convinced on this steam valve theory,although I can see that
>it could logically self regulate,by that fashion for each
>power stage.IE D.slow,slow,half,full,once the main control
>rods are adjusted to the settings for each output. Actually, you have it reversed. Open throttles for ahead full and reactor follows. Once at the bell, shim rods a bit to correct for any slight deviation in temperature. Compensate for Xenon buildup/burnout over the next several hours with rods to maintain temperature. But you're already answering all ahead full.The reactor won't always follow exactly. It will end up at the right power level, but it may be slightly cooler/hotter than desired. Over core life, many variables change that affect the exact reactivity. But it *will* follow and keep temperature within a few degrees of where it was at all-stop, supplying just hotel load.>
>However control systems being what they are,I'm sure a
>reactor can follow load quite happily,with the minimum of
>human intervention,apart for the sake of emergency action. But you still don't grasp the fact that naval units don't have active control systems. Rickover was dead set against automatic systems in the 50's. Didn't trust them. So instead, the reactor itself is designed for ease of operation. Control rods for startup and shutdown and long-term-reactivity management. But once in the power range, only needed to fine-tune plant temperature and compensate for fuel 'burnup' and fission product poisons.Rickover's navy abhorred automatic controls of any kind. The governor and voltage regulator on the generator sets was about the only process control. All control rod groups were manually positions from manuvering by RO. Whole engine room run by a handful of watchstanders. Reactor protection system is more of a logic control. Reach the set-point on enough channels, and *whack* you get a scram. Relays and bi-stable mag-amps were the order of the day.>
>As PWR's have this amazing ability to self regulate,or is it
>only submarine reactors?,I would have thought that this
>feature would be on top of any list of rebuttal statements
>against those opposed to nuclear power.Again a big silence. Actually, commercial PWR's *do* use negative temperature coefficient effects. The reactor operator changes reactor power by dialing the desired MW load into the turbine control system. The turbine controls ramp the steam valves open slowly (commercial can't run up/down like naval). The reactor cools, and power follows steam demand. In commercial, a bank of the rods are set to automatic. The input to the rod control system is Tave (average temperature of hot-leg and cold-leg). Rods are 'stepped' in and out based on changing Tave. The physics are not as responsive and rods have to move more to maintain temperature, but the basic principles are still there.Interestingly, BWR's are *not* like this. In BWR's the turbine controls are set to maintain steam header pressure. The reactor operator uses a combination of changing core flow and control rods to raise reactor power. The turbine valves open in response to rising steam pressure.PWR's 'the reactor follows the turbine' and in BWR's 'the turbine follows the reactor'. What a world!!!!Controlling reactor power with steam demand does *not* remove the risks of nuclear power. Decay heat can melt a core quite successfully even with all control rods fully inserted. Three Mile Island is a perfect example of that. The control rods were inserted and the fission process completely shut down, yet the core was significantly melted later by decay heat and a lack of cooling.Reactors with negative temperature coefficient are what make nuclear power possible. If not for this, even the pro-nuc engineers would cringe. But the politics of nuclear go way beyond the type of control used in the reactor.>
>I have found a site that deals with reactor controls for
>marine reactors,
>http://wwwsoc.nii.ac.jp/aesj/publication/JNST2001/NO.7/38_557-570.pdf
>
>and it states quite clearly,on page one,that the primary
>reactor control for manoeuvering the vessel is the control
>rods,and obviating the need for chemical shims.No, what it says is "In general, the reactor power of large scaled PWR for electricity generation is controlled by chemical shim and/or control rods..."The paper doesn't take the time to explain *a lot* of things about reactor control, but rather why internal CRDM mechanisms would be desirable. The authors assume a certain level of background understanding of reactor theory (which you lack). They aren't trying to explain reactor kinetics to John Q Public.*YOU* interpret a paper who's main treatise is in explaining features of an internal CRDM, as if it covered all of reactor theory. If it were this simple, everyone could operate a reactor and licensing would be a snap.Rods *are* used for startup, heatup and shutdown. They are also a key part of reactor protection systems. They compensate for fuel 'burnup' and fission product poisoning. In some reactors, they also compensate for steam void formation.> I assume the
>shimming mentioned previously onboard submarines is of this
>variety,and not brass. Neither. Chemical shimming in commercial PWR's is the dilution/addition of boric acid in the primary coolant (yes, an acid). A major isotope of the element boron is a strong neutron absorber. By diluting/adding boric acid concentration, overall reactor power can be raised/lowered, allowing the insertion/withdrawal of control rods to restore the power. This long-term 'shim' allows operation with the control rods in essentially the same place at full power even as fuel is consumed. This is valuable in being sure to 'burn' the fuel as completely as possible.In naval units, and many others, 'shimming' a control rod refers to the slight mechanical movement in/out used to compensate for various effects and restoring temperature to desired band (the infamous 'green band')Brass is not involved, but boron, boron-carbide, hafnium and zirconium are (and a variety of steels)>
>Therefore,once again,until I see actual documentary evidence
>of the steam valve theory,rather than anecdotal
>evidence,I'll stick with my perception of reactor control. There are several classic texts on reactor kinetics and control. The 'red book' of Glasstone is perhaps the most famous. You can probably find it in your local library. Naval reactor kinetics are still mostly classified. But if you ever run across some other old navy nucs, they *may* be willing to share some more 'anecdotal' evidence with you.Your perceptions are your business. But this is one of the problems with letting the public make decisions about complex technical issues. You can't make rational decisions because you don't have enough information. And alhtough a few people here have taken a little time to teach you a few things about reactor kinetics, you seem unwilling to believe them. Perhaps a couple of good college courses would suit you better. University of Wisconsin and MIT both have fine nuclear engineering programs. Enjoy.

Mike F

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"No, what it says is "In general, the reactor power of large scaled PWR for electricity generation is controlled by chemical shim and/or control rods...""IE the current system in operation in land based reactorsBy selectively quoting the above,you should have then quoted the actual control system used in marine reactors,obviating the use of chemical shims.IE "A marine reactor,however,adopts the reactor control system using only the control rods,since rapid response of the reactor power is required for heavy and frequent load change due to the load change of ship propulsion..."After them,the authors,stating "only control rods",they then quite rightly,as a commercial company,go on to justify why their control rod actuators should be those used in such a nuclear marine plant.Your statements regarding "automation" being abhorred in the US navy,especially submarines,is interesting,but then again due to classification purposes,it may be better to allude to a simple steam valve theory to hide the complexities of the actual control systems involved.Certainly,in the commercial shipping world,automated control systems have been welcomed,and embraced,and certainly,as a seagoing Chief Engineer myself,I can attest to their efficiency,in that engine rooms can,and are,being run unattended for sixteen hours per day,whilst on passage.
They technically do run the full twenty four hours,per day automatically,for weeks at a time,but maritime law,and classification society rules demand that for eight hours per day they are supervised in operation.This leaves all engineers free to only do daywork,although nominally a rota engineer is "on call",in his bunk,to answer any alarms during that sixteen hour unmanned period.However during vessel manoeuvering,and in restricted waters,the engine room is manned,to ensure that manual overiding of the control systems will take place,if circumstances dictate.Other than that he watches the boiler\turbines,or main propulsion diesel engine do their stuff without actually intervening.This arrangement means that,for British registered ships anyway,only three,but usually four,engineers are sufficient to run the most complex cargo,container vessels.It also means that the engineers concerned must be fully conversant with the control systems used for such applications,as if they weren't,chaos would soon reign.I had the pleasure?,of joining just such a vessel,a Panamax bulk carrier,where the automation was so shot(We had just purchased it from previous owners),that it took three watchkeepers per watch to keep it going,one senior,and two junior engineers,not forgetting an African oiler too.
By the time I left,eight months later,the vessel was working so well,under automation,and with normal manning levels,as far as engineers were concerned,that it was chosen to be converted to a car carrier to take vehicles from Japan to the USA on a strict penalty time charter.And this it did,with complete success,until no longer required.It is from this control background,that I still dispute the simple steam valve theory,for fully automatic reactor control.

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>Your statements regarding "automation" being abhorred in the
>US navy,especially submarines,is interesting,but then again
>due to classification purposes,it may be better to allude to
>a simple steam valve theory to hide the complexities of the
>actual control systems involved. Since I qualified as Engineering officer of the watch, and was also in charge of electrical maintenance (both at sea and during refuelings), and several other qualifications, *I* know that it is not some theory that was just 'alluded' to in order to avoid discussing classified information. I had to trace every circuit for the control rod drive system, reactor instruments and reactor protection. Explain each circuit in detail to the Captain before he would sign me off. *I* know exactly what moves a control rod and when. Once qualified on the power plant, still had to qualify submarines.But it is plain that *you* would rather believe that you're right and the rest of us are wrong. And since you can't admit you don't know very much about nuclear reactors (of which I've been working with for over 30 years), I guess you can just remain the arrogant, ignorant person that you are.Naval Nuclear Power has been around for over 40 years. Rickover also required operators to only learn on the real thing. No simulators were allowed. If you couldn't operate a real reactor plant, even while under instruction, he didn't want you. That much has changed, simulators are now used for some training.Similarly, your engine room wasn't as automated 40 years ago either. Commercial ships have an incentive to automatic, it saves them labor costs. Warships would rather have sailors than can understand and operate the ship, even when on fire, flooding, or under attack. Commercial sailors abandon ship.>
>However during vessel manoeuvering,and in restricted
>waters,the engine room is manned,to ensure that manual
>overiding of the control systems will take place,if
>circumstances dictate.Yep. And in the Navy, 'station the manuevering watch' was a welcomed announcement coming back from a long patrol. More than doubled the watchstanding (extra navigation party, manned DC stations, even an extra log-taker for the engineer's 'bell book'). But it meant we were close to home.But since the engine room and machinery spaces on war-ships were a pretty much 'manual' operation (especially nucs, although newer gas-turbine units are very automated), the watch wasn't set because of fear of some control failure (well, okay, the feed-station maybe). Collision, sudden failure of steering, crazy sailboats were more of a concern.>It is from this control background,that I still dispute the
>simple steam valve theory,for fully automatic reactor
>control. Your 'control background' doesn't count for anything in nuclear physics. Since working commercial, I've learned quite a bit about process-controls and instrument loops too. You don't see me spouting off that since we use 10-50mA loops, your ship *must* use them too. Or that all boiler level controls use three-element control just because ours does.You so much as admitted that control systems sometimes fail. Reactor safety is not something to take lightly. Neither is safety of ship. A sub loses propulsion, it can very easily die (e.g. "USS Thresher" SSN-593). Can't wait to wake up the 'on-call'.Maybe you should go *READ A BOOK*. And *more* than some GRADE-SCHOOL PRIMER on nuclear power. Get past this dogged fixation of yours that only control rods control the chain-reaction. Learn some of the *other* aspects of reactor kinetics.Once you've learned what these terms are and how they affect a nuclear reactor, come back and we can have an intelligent conversation.Moderator Temperature Reactivity Coefficient.
Void Fraction Reactivity Coefficient
Doppler Reactivity Coefficient
Delayed Neutron Precurser Half-life
Delayed Neutron Fraction
Thermal Utilization Factor
Resonance Escape Probability.
Core Inlet Subcooling
Power Reactivity Defect
Xenon Worth
Sumarium Concentration
Buckling
Mean Free Path
(and one of my favorites...)
Average Logrithmic Energy Decrement.
(hint: They *all* have to do with controlling reactor power, and only *one* of them is directly affected by the control rods. Can you figure out which?)If, on the other hand, you wish to remain blissfully ignorant and stick to your *inaccurate*, *assumptions* about nuclear reactor operations, well, that's your choice.
Do you *really* think that several of us made this all up, or do you think you know more about operating a reactor than those of us who have done it? Either way, it makes you a bit of a $%$@#$@.(p.s. to Chuck, don't worry these are all from Glasstone's, available in most college libraries)

Mike F

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LAST EDITED ON Oct-06-03 AT 09:25 PM (EDT)

ROFLMAO!Don't worry Mike, I'm not! You'll have to forgive Larkie as being a Scot he's a wee bit thick when it comes to admitting he's wrong about anything, be it politics or engineering! LOL!Just think of the lads of Dunoon while in their cups, staggering about High Street and I rest my case!
Chuck Schneider
(Virtual) CEO
North American (Virtual) Locomotive Works

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I think all nuclear power should be done away with. 1 its bad for the planet. 2 its dangerous. Whats wrong with wind power or solar power or hydro thermal?Stephen White

Oh and have a nice day.

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>I think all nuclear power should be done away with. 1 its
>bad for the planet. 2 its dangerous. By that standard perhaps the human race should be done away with. As it is dangerous and seems to be bad for the planet it meats your criteria and would eliminate nuclear power as well.> Whats wrong with wind power or solar power or hydro
>thermal? First, capacity. Second, as above, they can be bad to the planet. Perhaps one of our New Zealanders can speak to the Wairakei and Tauhara geyser basins. I have only the brief sentence that they were destroyed by geothermal development. Also El Tatio, Chile, Lardarello, Italy, and Steamboat Springs, Nevada. We have no idea whatsoever how much energy we can pull via windfarming without disrupting the weather patterns. In short, the electricity generated is never "free" the energy is taken form somewhere, and the extraction of such energy will always have side effects on whatever it is being extracted from.
Brad Meyer

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Brad don't be too hard on the poor kid.
He is only parroting what his teachers told him and he doesn't have enough life experience to separate the wheat from the chaff yet.
IMHO we are now paying the price for the draft dodgers and tree huggers hiding in Academia in order to avoid making a real contribution to society.
note: this does not mean Teachers as a class are non-productive, just that we have seemed to "herd" a large percentage of the non-productive members of society/self declared elite into that profession....
Sheesh talk about junk science....Chuck Schneider
(Virtual) CEO
North American (Virtual) Locomotive Works

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LAST EDITED ON Oct-07-03 AT 06:42 PM (EDT)

I think I can hear the the tree-hugger's mantra: "If It's Nuclear It's Evil"Stephen, in more than 35 years of nuclear power generation, Three Mile Island is the only major accident in the US that I can remember. As for the military's use of nuclear reactors to power their ships and submarines; I cannot think of a single major reactor accident aboard a NATO vessel.
Even without the accidents, nuclear power still has it's drawbacks, most notably storing the spent fuel. So Stephen, I partly agree with you: We should ditch nuclear power, but only after a viable peplacement is available, namely fusion power. Using fusion power for electrical generation is still years away, though. At present, a fusion reaction will suck about three times as much power as it generates. Until it is ready though, we should stick with nuclear power, because the alternatives are either too dirty (coal power), and the ones you mentioned are too unreliable and lack sufficient capicity.
Remember, even with the Chernobyl and TMI accidents, nuclear power has caused less net harm to the environment than it's predessor, coal BTW, I live between two nuclear generating stations (Darlington and Pickering), and I don't feel nervous about that.Now on to a related topic, who wants to delve into the "Depleted Uranium is Evil" debate? Jonathan Nikiforovs.
Milepost 180, CP Belleville Sub.Repainter for Yonder Locomotive Works.

"A crictic is a man who creates nothing and thereby feels qualified to judge the work of creative men. There is logic in this; he is unbiased - he hates all creative people equally." - Lazarus Long

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>Brad don't be too hard on the poor kid.I am hoping this is written with tounge in cheek. If not, I apologize both to you and him and to the readers of this forum in general. It was not my intent to be "hard", only to point out some (what I felt were) pertenent facts for his consideration. >note: this does not mean Teachers as a class are
>non-productive, just that we have seemed to "herd" a large
>percentage of the non-productive members of society/self
>declared elite into that profession.... Maybe GB Shaw was right. FWIW, I think the issue is less the quality of the teachers themselves then one of the educational system (at least in the USA) changing its primary mission. I'm a fifty-something and did my K-12 in the 1950's and early '60's. Looking back at it, I can clearly see that the main focus was in training students how to think. In other words their task was to help students discipline their intellect. Nowdays, it seems the focus has shifted to trying to teach students what to believe, and IMO nothing destroyes the ability to reason accurately then having a set of belief structures without the logical foundation behind them cluttering up the thought processes.>Sheesh talk about junk science.... IMO not so much junk science as incomplete science. As I pointed out, there is a cost benefit equation to any form of energy production. I believe it behooves anyone claiming an informed opinion on the subject to understand the actual (and potential) costs and benefits of all forms of energy production. It only becomes junk when the rational gives way to belief structure.Brad Meyer

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I agree wholeheartedly. Ban dihydrogen monoxide while you're at it; that stuff has been killing for thousands of years, yet people are surrounded by it and the government refuses to act to stop deaths by DHM. Unless the world community unites under the flag of the United Nations, we will be faced with the dangers of DHM forever.Question about the loss of energy in generation: I take your remark about windfarming to mean that if the wind's blowing at 60MPH "before" it gets to a windmill, it will inherently be blowing 60-something "after" it passes through the windmill, the reason for that being that some of the energy contained in a 60MPH wind is lost turning the blades of the windmill, correct? I'd never heard that argument about wreaking havoc on global weather patterns as a result of windfarms. That's actually kinda scary. At least we can fix a reactor spill.

____________________________________________________________________
Norfolk & Western’s Radford Division, Pulaski District: Who needs the Marias Pass?

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>I'd never heard that argument about wreaking havoc on global
>weather patterns as a result of windfarms. That's actually
>kinda scary. At least we can fix a reactor spill. You would need a huge amount of windmills to change climate on a global scale, but the fact is the theory is sound. Wind has kinetic energy, and a windmill takes away some of that energy to turn into electricity. In layman's terms, it reduces wind speed. It may also change wind direction slightly. Slight changes in wind speed and direction may cause huge changes in climate(i.e. the old somewhat exaggerated adage about a butterfly flapping it's wings somewhere leading to a hurricane somewhere else).I wouldn't sweat over this too much. Few areas are suitable for massive use of wind power anyway.Regarding Stephen White's post, you can't use wind or solar for everything. Granted, they should be used more than they are, but they can't satisfy 100% of electrical demand. Solar might fit the bill eventually, but for now solar cells are still too costly and inefficient for general adoption except in very sunny areas. They might pay to use on single family homes in areas where electricity is costly as well. When fusion becomes viable uranium fission will be obsolete but until that time it's the best means of generating electrical power.It's important to remember that the worst nuclear accident in history(Chernobyl) killed at most thousands of people, and more likely only hundreds. Coal and oil fired plants(as well as automobiles and planes) spew pollutants into the air that kill millions through cancer each and every year. Which would you rather have? It's funny how the so-called environmentalists conveniently ignore this fact. Even more funny how many of the Hollywood "save the rain forest" types pull up at award ceremonies in block long limos spewing heaven knows what into the air. These people are the very definition of hypocrite. Yes, I consider myself an environmentalist, but I like nuclear power. I am also very annoyed that environmentalists picked global warming as their poster child instead of using more valid(and scientifically sound) reasons to ban fossil fuels such as cancer, asthma, acid rain, toxic runoff from roads, etc. Why pick an unproven theory when so many other good reasons already exist? If nothing else, polluted air smells bad, and that's already a good enough reason to not use fossil fuels in my book.

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LAST EDITED ON Oct-07-03 AT 10:44 PM (EDT)

Well, internal combustion engines as we know them may have their days numbered, with the advent of fuel cell technolegy. The newest fuel cell engines don't need pure hydrogen to run, they can accept any fuel with hydrogen (all fossil fuels contain hydrogen) in it, although each engine must be modified for various types of fuel, though. IIRC, the US military is looking in to getting a version designed for their standardized JP4 fuel.Jonathan Nikiforovs.
Milepost 180, CP Belleville Sub.Repainter for Yonder Locomotive Works.

"A crictic is a man who creates nothing and thereby feels qualified to judge the work of creative men. There is logic in this; he is unbiased - he hates all creative people equally." - Lazarus Long

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>Question about the loss of energy in generation: I take your
>remark about windfarming to mean that if the wind's blowing
>at 60MPH "before" it gets to a windmill, it will inherently
>be blowing 60-something "after" it passes through the
>windmill, the reason for that being that some of the energy
>contained in a 60MPH wind is lost turning the blades of the
>windmill, correct?Something like that. My point is that if you produce energy from a wind farm, that energy has to come from somewhere. Tanstaafl. It isn't created in the wind turbine, it is converted from the kenetic energy of the moving air. Pulling a couple of hundred kw worth of enegry seems to have little or no effect. OTOH, pulling a couple of thousand Mw worth may be an altother different proposition. I don't know, and from what I have been able to read, no one else does either. I jsut think we ought to find out before we go to hitching our energy wagons to this particular star.>I'd never heard that argument about wreaking havoc on global
>weather patterns as a result of windfarms. Frankly, me too. It is the fact that I haven't heard anything that I find most scary. It may well turn out that taking what we might think of as a huge amount of energy from the atmosphere is not huge in atmospheric terms. OTOH, there seems to be clear evidence that putting a lesser amount of energy into the atmosphere, in the form of waste heat, is having a direct effect on weather and climate.

Brad Meyer

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