Vaughn said:
You just need a moderator that changes density inversely with
temperature, and then virtually no rod movement is necessary to
change power. As you draw heat from the reactor, the moderator
cools a bit, increases density, automatically raising the core power
level. If you stop drawing power, the moderator heats up a bit, gets
less dense, and the power level decreases. The naval PWRs that I am
familar with have throttle response that is plenty good enough for
ship manuvering.
I'm quite aware of using negative moderator coefficient to control power.
Commercial PWR's also use this feature. But fuel temperature causes a lot
of negative feedback in low-enrichment reactors. Naval units have the
advantage of not having very much U-238 (cost of high enrichment is
'justified' on the ground of mission statement).
The research project I was referring to was able to ramp from sub kW to
about 2 MW in under 5 seconds, hold that power a precise amount of time and
then 'push' power back down to sub kW. Normally, power reduction would be a
problem thanks to some physics and a -1/3 SUR (or in BWR 'speak', a -80
second period).
Now, can you think of some government project that would be interested in
that sort of 'pulsed' power?? ;-)
The real problem (besides that minor radiation & safety thing) with
a small reactor is they don't yet make nuclear reactors with handy
crankshaft couplings sticking out of them. Nuclear reactors are
really just a heat source, so you still need a heat engine to do much
useful with them.
This project wasn't interested in a steam plant, but the 'minor radiation'
had some uses.
BTW: There have been several fission nuclear reactors launched into
space, so they don't need to be all that big.
Are you sure they were 'fission'? Many TNG's, but they weren't really
'fission reactors'. ISTR Voyager was one that was a 'concern' at the time
because it contained a toxic fuel, Pu.
daestrom
