I posted this on my Japanese blog for the Japanese readers. I'm putting out the summary for the English readers here, too.
A nuclear researcher at Kyoto University (which is considered one of the two most prestigious national universities, the other one being Tokyo University) has reversed his opinion and now says the Reactor 1 may be experiencing the "recriticality".
His name is Hiroaki Koide, assistant professor at Kyoto University's Research Reactor Institute who belongs to the Nuclear Safety Research Group at the Research Reactor Institute. He has given interviews on TV and radio, mostly in Kansai stations and not aired in Kanto (where Tokyo is), and would be considered one of the "sceptics" of the official story about Fukushima I Nuke Plant that everything is safe, getting under control.
There ARE researchers in Japan who go against the mainstream government scholars. Koide is one of them (and far from being the most critical), and there are others from universities other than the top few schools (and therefore they don't get hardly any airtime on the Japanese MSM). But thanks to talk radio shows and the Internet (hey it's the same as in the US), at least a small portion of the Japanese people are getting the "alternative" reality other than what's given by the government and the MSM.
This is from the transcript of the interview (in Japanese, NOT the literal translation) Koide gave on April 5, 2011 on Osaka's MBS Mainichi Broadcasting Radio:
"The Fukushima I Nuke Plant accident is not winding down at all. I think I have to revise my opinion which was too optimistic."
- What was too optimistic?
"We thought the reactors "cold stopped", which means the uranium fission stopped. But now I've started to think the fission has started again. In other words, the reactor has become "critical" again - which we call "recriticality"."
- Professor Koide, you were of the opinion that the recriticality was not happening.
"Yes, and I've changed my mind. It may be happening."
- On what evidence?
"First, the level of iodine[-131] is not decreasing; it is increasing. Iodine[-131]'s half life is 8 days. It has been more than 3 weeks since the accident, so the level of iodine[-131] should be about 1/10 of the initial level measured. Second, the presence of chlorine-38 was detected from the contaminated water in the turbine building [he doesn't say which one]."
- What about chlorine-38?
"Well, if chlorine-38 was detected [according to TEPCO], and that can only mean "recriticality".
Chlorine-37 is a stable isotope, and it exists in salt in the sea water. TEPCO had poured literally tons and tons of sea water into the Reactor Pressure Vessels at Fukushima. The way the stable chlorine-37 becomes highly unstable chlorine-38 (half-life 37 minutes) is for chlorine-37 to acquire neutron.
The only way for neutron to be present near chlorine-37 is for uranium to go critical and emit neutron.
That's what Fairewinds Associates' Arnie Gunderson said in his April 3 video, and that's probably why IAEA mentioned the possibility of "recriticality" on March 30.
Koide thinks the recriticality may be happening in the Reactor 1 where the fuel rods may have been melted down most (Koide thinks there is no cladding left, and the tiny uranium pellets are forming a heap at the bottom of the RPV), but says the other two reactors (2 and 3) are also vulnerable if TEPCO cannot cool them sufficiently and the core melt continues.
He also suspects TEPCO is not pouring enough boron to prevent fission.
Maybe that's another item at Fukushima I that's missing: boron.
It took almost 3 weeks for TEPCO to admit they didn't have enough dosimeters for the workers.
Don't hold your breath for a TEPCO's announcement that they are out of boron. Maybe they can dump bath salt in the pressure vessels and that may stop the fission.
And remember, repeat the mantra of the Japanese government: it is safe.