Not funny anymore
- Feb 6, 2008
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Just curious. I don't know much about this style reactor, obviously nothing like the pressurized water plants on my Enterprise.
What is the heat sink for the fission products after shutdown? Of course that can be minimized if it was run near idle for a substantial time before shutdown.We ran the turbogenerators until residual product output decreased enough, then dumped steam to the main condenser. Would the coolant pumps with radiators to space be enough heat sink? Are you planning on criticality be used to heat the reactor or just use the coolant pumps. We used the coolant pumps and fluid friction to heat up the plant before pulling rods.
I think it'll be interesting to play with this one.
Never mind the shutdown part, I just realized your #106 where you said you'll ignore decay heat for now.
No, its more like a gas-core reactor, running on a mixture of Helium and Xenon (HeXe, Helium for heat capacity, Xenon for density), with a single primary loop running in the Brayton cycle, not the Rankine cycle like a PWR does. The Brayton cycle is what gas turbines use. Also, the moderator is not water in this case, but a carbide at low power operation (for producing electricity) and hydrogen gas in high power mode.
Since it is operating on gas, the compressor already puts some amount of heat into the coolant by its operation, when bypassing the radiator during startup, this should be able to quickly heat the reactor to about 600K. Its just maybe 50 kg of coolant in the system, including 16 kg in the 600 psi accumulator tank to compensate changes in volume during operation. While the reactor is slowly heating up, small amounts of liquid hydrogen are passed through a heat exchanger, turned into gas and starts filling up the other tie tubes in the reactor and adding a small amount of moderator more.
From this point on, the control drums are slowly rotated to expose more reflector surface, until reactivity has climbed high enough to let the reactor become critical. In low power mode, the reactor power should mostly depend on delayed neutrons, like in a PWR, but in NTR operation, this seems to change towards a fast reactor type of operation.
From what I can tell from how a SCRAM was supposed to work, the simplest solution to the residual heat was to pulse hydrogen through the engine (producing tiny amounts of thrust) for rejecting heat until the HeXe coolant loop was able to handle the coolant alone. An intermediate step could be using the hot hydrogen gas attitude control system for dumping hot hydrogen gas from the reactor tie tubes without producing net thrust. Because of the small size of the reactor, the ultimative way to stop the chain reaction would be explosively ejecting the control drums from the reflector, increasing neutron leakage. As long as enough drums leave the reflector (just 1 or 2 would be fatal), the reactor would stop.
I'll add decay heat later, in first place, it is now about producing a good enough model for going on with the rest of the spacecraft.