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Wednesday, November 2, 2011

Xenon detected at Fukushima Daiichi No. 2 again

DEVELOPING STORY

A second sample run at Fukushima Daiichi No. 2, a day after the first, has detected Xenon-135 but failed to detect any Xenon-133. Below is a very fresh chart from TEPCO.


This is good news in one way, in that one of the isotopes was not detected. Some Japanese outlets are still reporting that TEPCO wants NISA to assist in a re-evaluation of the samples since it believes (or believed at some point) that perhaps some error in reading may have indicated Xenon in place of another element entirely.

TEPCO's latest, very new, press release (3 PM Tokyo, November 2) gives no data at all either about the Xenon detection or the boric acid injection. It also omits the injection rate change and gives the old one. Clearly this press report is in error (probably a clerical error omitting the new entries for No. 2) and I'd expect this to be amended or replaced.

TEPCO will be checking the other two plants (No. 1, No. 3) with reactor cores installed for presence of Xenon.

While some outlets continue to use the term "critical" in reference to No. 2 plant and the fission event leading to the Xenon production, it is imperative to understand that no sustained nuclear chain reaction occurred. No site radiation monitoring equipment detected anything alarming or even spurious. No increase in temperature or pressure was noted. The condition of the remains of the core are just not likely at all to be able to sustain any kind of chain reaction / fission rate... considering the mixture of non-fertile and also poisonous (neutron-absorbing) materials now melted integrally in and around the fuel material.

Also... for our non-nuclear friends... the Xenon generated in fission is normally contained inside the fuel elements (be they rods, plates, or other) and decays or absorbs neutrons to move down the chain to a stable element. It remains there permanently. Only because the core materials are damaged or melted at Fukushima Daiichi No. 2 is the Xenon which is produced able to get out into the water and air volume inside the plant at this time and thus be detected by the gas sampling equipment. The effects of Xenon on reactor operation are well known but normally the Xenon is NOT emitted.

At this time there are no changes in detected radioactive materials on site or off site, no alerts off site have been made, and conditions operationally on site are as they were before this recent event.

More details when available.

8:30 AM Eastern Wednesday November 2, 2011
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3 comments:

  1. Could you comment as to your opinion? Do you think xenon is being produced in the reactor? If so, is the xeon produced by fission of some other process?

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  2. @martin: Yes, I believe that the xenon was produced as a result of fission on a VERY limited scale. The half life is short enough that it seems unlikely to have been there since the accident, and both TEPCO and NISA apparently agree on this fact. Whatever the case, we are opening a new phase of accident recovery (which is not entirely unexpected) with this finding and the response to it and you can be assured many more tests on No. 2 and on the other two plants will be immediately forthcoming to determine the root cause of these findings. Having said all this, I myself do not believe that any emergent danger exists because of this either right now or in the future. The recovery will continue as mapped out by TEPCO, NISA and the Japanese government.

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