Criticality Accident?

Things are getting better and better all the time when it comes to the Japanese Nuclear Reactors in Fukushima. Take this report from 19 March, 2011.

-- Reactor No. 4 - Under maintenance when quake struck, no fuel rods in reactor core, temperature in spent-fuel storage pool reached 84 C on Monday, fire Tuesday possibly caused by hydrogen explosion at pool holding spent fuel rods, fire observed Wednesday at building housing reactor, pool water level feared receding, renewed nuclear chain reaction feared, only frame remains of reactor building roof.

The Monday and Tuesday in question would be the 14th and 15th.

OK. Now we get this wonderful bit of news from 23 March that ties in with the old news.

Tokyo Electric Power Co. said Wednesday it has observed a neutron beam, a kind of radioactive ray, 13 times on the premises of the Fukushima Daiichi nuclear plant after it was crippled by the massive March 11 quake-tsunami disaster.

TEPCO, the operator of the nuclear plant, said the neutron beam measured about 1.5 kilometers southwest of the plant's No. 1 and 2 reactors over three days from March 13 and is equivalent to 0.01 to 0.02 microsieverts per hour and that this is not a dangerous level.

Well isn't that interesting? Not at all. Look at the attribution of the beam in the latest report.

...the measured neutron beam may be evidence that uranium and plutonium leaked from the plant's nuclear reactors and spent nuclear fuels have discharged a small amount of neutron beams through nuclear fission.

The neutron beams are evidence of criticality. Random bits of U235, U238, and Plutonium scattered about the universe do not generate neutron beams. I'm sorry. But unless you have neutron multiplications of above 1.0000 you are not going to see a lot of neutrons coming out of a "shut down" reactor. And it might not have been a reactor even. Spent Fuel Rod Pool #4 is a prime candidate. The "pile" need not be very orderly if the pile is big enough. Such disorder in fact might very well generate beams rather than the more even flux you get from a reactor operating as designed.

Of course criticality accidents are very bad news. Because there is no guarantee that the "pile" will not restart at some later date. Very inconvenient.

Oh. Yeah. Just for the record. It never happened, sort of.

In the latest case at the Fukushima Daiichi nuclear plant, such a criticality accident has yet to happen.

Of course it hasn't happened. If it had actually happened the news would be very inconvenient. Proof positive it never happened. And the Emperor willing it is not going to happen under any circumstances.

Han Solo: [sounding official] Uh, everything's under control. Situation normal.

Yeah. Right.

Cross Posted at Classical Values