Wednesday, November 2, 2011

Xenon in Reactor 2: TEPCO Now Says "Spontaneous Fission" of Curium

After confidently saying it may have been criticality in the press conference on November 2, TEPCO's Matsumoto now says it is spontaneous fission of curium in the reactor.

On the other hand, the Nuclear and Industrial Safety Agency, who was skeptical of criticality yesterday, now says, "We cannot rule out the possibility of localized criticality."

OK it's a "good cop, bad cop" routine, or a "covering all the bases" approach. If both "spontaneous fission" and "criticality" are mentioned in the same news, the Japanese government/TEPCO can say "See, we told you, either way."

From NHK News (11/3/2011):


Regarding the radioactive xenon detected from the gas inside Reactor 2 of Fukushima I Nuclear Power Plant, TEPCO revealed that the analysis of the amount of xenon detected led the company to conclude that it was a natural fission of a radioactive material, not criticality where nuclear fission takes place continuously.


The gas from inside the Containment Vessel of Reactor 2 was sampled and analyzed on November 1 and 2. A minute amount of xenon-135 was detected, and TEPCO said it was possible that there had been a recent nuclear fission, and that the localized criticality took place temporarily.


Since curium-242 and curium-244, the radioactive materials which exist in nuclear fuel, undergo natural fission and generate xenon, TEPCO calculated the density of xenon based on the amount of these nuclides. The calculation mostly matched the density detected from the samples.


According to TEPCO, the density of xenon would be much greater if there was a criticality. Xenon this time therefore is from spontaneous fission, not from criticality, says TEPCO. "Spontaneous fission" is a phenomenon in which radioactive materials other than uranium fissions naturally, and it does not cause criticality. TEPCO says it will submit the report of the findings to the Nuclear and Industrial Safety Agency under the Ministry of Economy, Trade and Industry, who will evaluate whether the conclusion is appropriate.


The NISA spokesman Yoshinori Moriyama says about TEPCO's analysis, "We think it is highly possible that it is a spontaneous fission, but we cannot rule out completely the possibility of localized criticality. We would like to evaluate TEPCO's analysis as well as analysis by experts. We will assess various risks and make sure TEPCO has emergency measures ready, including injecting water with boric acid."

Uh... what about krypton-85? Is this produced in spontaneous fission of curium? If it is spontaneous fission, why was not happening on October 28?


Anonymous said...

Spontaneous fission. Of course. And that worker months ago died of acute leukemia.

arevamirpal::laprimavera said...

Yup. They have a big credibility problem here, but at this point, they don't even pretend that they care about that problem.

Anonymous said...

Krypton-85 is produced by fission. Could be spontaneous, could be a chain reaction.

shusse said...

Could be a publicity stunt - crying wolf and acting concerned for the sake of media attention. And behold, a quick sigh of relief the next day. Catch and release. Also, when a real criticality happens it won't be such breaking news any more. Win-win for Tepco.

"If it is spontaneous fission, why was not happening on October 28?" - The first analysis was on November 1.

shusse said...

Ah, about my previous comment - "The first analysis was on November 1", I apologize. I misread the article. Tepco handout shows a reading from Oct 28 with xenon "below detection limits".

Anonymous said...

"why was not happening on October 28?" Tepco did not say that it was not happening. Tepco used a measurement method with a very high detection limit on October 28, so that the amounts of Xe, if there were any, could not be detected. On November 1 and November 2, the detection limit was lowered and only then could the small quantity of Xenon be detected. See "Detection limits" in

arevamirpal::laprimavera said...

@anon at 5:31PM, excellent. Looking at the tables, I just noticed TEPCO used the higher detection limit for Xe-133 on November 2, so Xe-133 was below that higher detection limit.

Anonymous said...

"I just noticed TEPCO used the higher detection limit for Xe-133 on November 2, so Xe-133 was below that higher detection limit."

You don't "use" detection limits. Detection limits vary from test to test, depending on the device used, the volume of the sample, the time employed and noise present on the gamma spectrum obtained.

arevamirpal::laprimavera said...

sorry wrong word. TEPCO tested at a different location on Nov. 1 and 2, and the testing was longer (30 minutes). I'm looking for the diagram of the gas detection system.

Anonymous said...

You mean this one?

Anonymous said...

Also, their report of the Xenon-135 affair:

arevamirpal::laprimavera said...

@anon at 8:52PM, yes, that was it. Thank you!

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