Recriticality Suspected at Fukushima Nuclear Site

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Japan Update: Recriticality at Fukushima Plant Site
by Nelle Maxey
Dear Readers, You will remember my discussions of the possibility of re-criticality in the reactors at Fukushima. I am sorry to report this is now a serious possibility at Unit 2 (and at Units 1 and 3 perhaps as well.)
For the first Time since the beginning NHK showed the Corium "under" the Cement Table
The releases of Xenon detected by the gas management system instruments are very small and TEPCO is downplaying this development as controllable by spraying boric acid to absorb neutrons and thus prevent further chain reactions from occurring.
Of course, as always, there are more questions than answers about what is actually going on.

Bloomberg:  Fission Detected at Damaged Fukushima Atomic Power Plant:

  “The company, known as Tepco, began spraying boric acid on the No. 2 reactor at 2:48 a.m. Japan time to prevent accidental chain reactions, according to an e-mailed statement today. The detection of xenon, which is associated with nuclear fission, was confirmed today by the Japan Atomic Energy Agency, the country's atomic regulator said.

  “Given the signs, it's certain that fission is occurring,” Junichi Matsumoto, a general manager at Tepco who regularly talks to the media, told reporters in Tokyo today.

  "Fission taking place in the reactor can lead to increases in radiation emissions and raises concerns about further leaks after another radioactive hot spot was discovered in Tokyo on Oct. 29. It's possible there are similar reactions occurring in the No. 1 and No. 3 reactors, the other cores damaged at the station, Matsumoto said.

  “Melted fuel in the No. 2 reactor may have undergone a sustained process of nuclear fission or re-criticality,” Tetsuo Ito, the head of Kinki University's Atomic Energy Research Institute, said by phone. “The nuclear fission should be containable by injecting boron into the reactor to absorb neutrons.”

[Sorry I forgot to include the link to Corbett’s excellent Fukushima Update pages.  (Must move it up from the bottom of my bookmarked pages list!) Fukushima Update – Day 237 Good graphics and extensive list of links
Source: -NM]

There are 4 headline stories at ENENEWS this morning on this story with various experts commenting:

  a.. JUST IN: Japan Gov't Confirms Detection of Radioactive Xenon in Reactor No. 2
  b.. "A very bad sign": 'Partial' re-criticality is just TEPCO spin -- "We could face…
  c.. Kyoto Nuke Expert: This amount of xenon would not be detected unless melted fuel…
  d.. Top Japan Nuke Expert: Sustained "re-criticality" of melted fuel may have occurr…

EX-SKF reports TEPCO thinks they can control the small criticality by carefully monitoring temperature and pressure.

More on Xenon Detection in Reactor 2 (TEPCO's Press Conference)
Fuku-I Nuke Plant: Nuclear Fission in Reactor 2? Xenon-133, -135 Detected

The Phyics Forum discussion is very interesting.

Most importantly, It may be the Xenon gas is being emitted by plutonium in the reactor and thus is not a re-criticality at all.
More questions:
- why a one-time injection of Boron would have no long-term effect if it is re-criticality
- levels of gas the same after the injection of boron as before the injection (Nov 1 and Nov 2 measurements)
- questions of how boron may affect the Areva chemicals reaction to decontaminate water
-calculations and measurements CAN be done to determine if it is a re-criticality


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