Thorium vehicle will run 100 years on 8 grams of fuel

[PamW]

20. WRONG AGAIN!!

johnd83,

If the fuel melts into a puddle it CAN NOT go critical. With the low enrichments of fuel in power reactors, the reactor core is RELYING on the heterogeneous lattice of fuel and water to aid criticality. The lattice dimensions are chosen to optimize the following neutron "life". The neutron is born in the fuel, and "leaks" out of the fuel into the water moderator. It slows down in the water moderator, particularly through the resolved resonance region. Only when the neutron is below the resonance region in energy does it re-enter the fuel to cause a fission.

In the region of a few keV to a few hundred keV, Uranium-238 has massive absorption resonances in the absorption cross-section. Log onto Brookhaven's Nuclear Data Center site and plot the absorption cross-section of U-238. If the neutrons slow down in the water, then there's no U-238 atoms around to absorb them parasitically. If the fuel melts, so that you have a fuel / water slurry then the neutrons will slow down in the presence of U-238 and its absorption resonances and will be parasitically absorbed, and it is therefore IMPOSSIBLE for the melted core to go critical. All this crap about melted cores going critical is just that; CRAP. The material mixture in a power reactor REQUIRES a heterogeneous core geometry in order to achieve criticality. ( Remember I used to DESIGN reactors when I worked for Argonne ).

Even in your accelerated-driven throrium reactor, the FUEL region will be where Thorium is transmuted into Uranium-233, and the U-233 is fissioned; so your FUEL will have fission products in it if there is no mechanism to instantly remove them. So even in an accelerator-driven thorium reactor, you will still have fission products in your fuel. When you shutdown the accelerator; you stop the fission energy generation. That's done in a power reactor by dropping the control rods; the fission energy production STOPS. But the reactor is still susceptible to meltdown due to the energy produced by the radioactive decay of the fission products; and the thorium reactor will have the SAME PROBLEM.

In both the Three Mile Island Unit 2 reactor meltdown, and the Fukushima meltdowns, the production of energy via fission STOPPED over an hour before the meltdown started. In TMI, the reactor was sub-critical for 90 minutes and remained unmelted as the coolant pumps cooled the core. The reduction in pressure due to the stuck safety valve caused boiling in the TMI core so that the fluid that was being pumped by the pumps was a two-phase steam / water mixture. The pumps don't like that, and make strange noises. At 90 minutes, the operators turned off the pumps because of those noises; and that is when the meltdown ensued. TMI was totally reversible until the operators shutdown the coolant pumps. In Fukushima, the reactors were shutdown at the time of the quake, and were being cooled by emergency power provided by the diesel-electric generators. When the tsunami broke over the plant an hour later, it flooded out the diesel-electric generators, and swept away their fuel tank which was above ground; and without electric power, the coolant pumps stopped, and hence commenced the Fukushima meltdowns. But in both TMI and Fukushima, the fission power had LONG been STOPPED. It was the power of the decay heat that melted those reactors; and your thorium reactor will have the SAME PROBLEM. If it produces energy, it is producing fissions, and that produces fission products, and those produce decay heat.

PamW