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17 March 2011

Notizie dall'interno

Subject: CMNS: My View 16 March on Fukushima Nuke Plant Accident
From: "Akito Takahashi"
Date: Wed, March 16, 2011 6:29 am

Dear all,
Here is my short report on the present (16 March, 2011, 14:20 Japanese time) status on the nuclear plant accident at Fukushima-I.

Yes, the situations of four reactors at the Fukushima-I plant are still serious for cooling in-core fuel-clusters and storage-pool-stored fuels.

There have happened "hydrogen-explosions" in #1 and #3 reactor-buildings, which destroyed upper part of building
walls and ceiling. Small hydrogen explosions also in #4 reactor, which was not operated at the time of the quake,
destroyed outer walls of the #4 building. Reactor vessels and containment vessels for #1 and #3 are safe. The containment vessel of #2 reactor may have crack somewhere downward to release steam including gaseous FPs to environment.

People of TEPCO are trying to cool, under high dose rates, fuels in every reactor by feeding pure and/or sea-water. Due to boiling of water somewhere, we see now steam cloud ejected from #2 and/or #3 reactors.

As the decay heat levels of in-core fuels are decreasing day by day, we expect the on-going cooling effort by feeding
water will make reactors more and more stable from now on, and we do not need to worry about "nuclear explosion" as
Chernobyl.

However, to confine radioactivity of stored FPs inside fuel-sheaths (zircaloy) we need to continue cooling to
minimize the release-and-diffusion to environment. Hydrogen gas was thought to be produced by the interaction between
high-temperature zircaloy and steam.

I think the situation will get to better and safer side day by day, in gross view. At the time of hydrogen explosions, there were leaks of accumulated FP gas in the upper part of in-side building, which caused one-through increase of dose rates at various
monitoring points in the east Japan area (Kantoh and Tohoku). The dose levels were not high to concern serious
effect to human body, and is now decreasing: There might happen similar leaks again, but we expect not so serious as
before.

I hope TEPCO, NISA and Governmental stuff, etc., will do their best to minimize the disaster, by continuing cooling
and recovering the plant electricity system. We have no actual problem, here in Osaka, except mental damage.

Regards, Akito

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