New Scientist says spent fuel pools at both #3 and #4 reactors at Fukushima I are both overheating.
Japanese authorities are now focusing their attention on preventing the pools that store spent fuel rods at the numbers 3 and 4 reactors from overheating.
Those pools now face a greater than zero possibility of criticality. It is, apparently, greater enough than zero that Tepco is considering adding boric acid to the water it’s spraying to cool the now-totally-dry spent fuel pools, because water is a neutron moderator — and makes it more likely that the spent fuel will reach criticality. Boron, contained in boric acid, absorbs neutrons and prevents criticality. Boron is used in the sheets between spent fuel rods in a spent fuel pool.
By the way, this shit flies in the face of established science. Spent fuel pools don’t go re-critical. They just don’t.
Except these are.
And the rocket surgeons that built these ones put them above the reactors. Above.
Apparently, they cover internet trolling but not GRAVITY at the universities that teach nuclear engineering.
From the BBC’s Richard Black:
The attempt to use helicopters and water cannon to dump seawater on to the Fukushima power station is almost certainly unprecedented in more than half a century of nuclear power.
The water was not destined for the reactors themselves – they are contained within containment systems that are designed to be sealed tight and which appear to be intact, with the possible exception of a crack in a vessel attached to No 3 reactor.
The targets were cooling ponds situated above the reactors, which store fuel rods. The ponds in buildings 3 and 4 – and possibly more – are certainly short of water, possibly completely dry.
OK, my Ph.D. is in psychology, so I’m not qualified.
This is a good site, and there should be more comments.
For old fuel the U-235 is gone, and I’ll assume little new Pu-239 was bred. This means there won’t be criticality from nucleus splits that eject more neutrons (Pu-239: 3; U-236, 2.4 on average) than they absorb (1). But the radioactinides are still decaying and making heat as you note. Fast neutrons from fuel rod-to-rod will increase the heat output. WATER will decrease the ability of one rod to activate another in a crowded pool because the actinides respond better to fast neutrons but water moderates / thermalizes neutron velocities. Pu and U are anomalous in having a large neutron cross section (a resonance) at low (thermal) energies.
The horror on my mind is that the fresher fuel in #4’s pool has more U-235, and that water without boron to absorb the neutrons would moderate them instead, and increase the fission and heat generation.
Thought you’d be amused to know that an 1100MW BWR-5 reactor like #6 running at full power would heat an Olympic sized swimming pool from freezing to boiling point in 54 seconds (using the electricity), and boil it all away in 9 hours. Of course, the heat input into the boiler has to be more watts than that in a plant with 36% overall efficiency (I’m being generous), so we boil away 1 Olympic pool every 2 1/2 hours making steam for normal operation. The question then becomes, how fast can we shut down big-time heavy industry like this? Students should consider in their answer the question of whether a nuclear reactor can ever be shut off in the sense combustion can. Sigh.
Thank you for that Union of C.Sci. data. Now I know the pools are only about half the size of an Olympic swimming pool.
The hydrogen explosions tell us the Zirconium fuel rod cladding is shot and the fuel and all the new isotopes generated in it by neutron flux is in the water, right? The fuel is loose uranium oxides (they’re not solid metal, I don’t think). So spray all that around? Plants 1 – 4 are write-offs. Why not order the concrete and bury them?