TEPCO to Redefine Its Idea of "Criticality"

Tokyo Shinbun (11/7/2011) reports:

東京電力は六日、福島第一原発の臨界判定基準を見直す方針を明らかにした。経済産業省原子力安全・保安院に先月提出した報告書では、半減期の短い希ガスが検出されないことを条件としていたが、今月二日に２号機で自発核分裂により発生したとみられる放射性キセノンを検出。実態と合わなくなり、修正を余儀なくされた。

On November 6, TEPCO disclosed its policy to review the standard to determine whether criticality has happened at Fukushima I Nuclear Power Plant. The report the company submitted to the Nuclear and Industrial Safety Agency under the Ministry of Economy, Trade and Industry defined the condition of criticality as whether noble gas with short half life was detected. However, radioactive xenon was detected in Reactor 2 on November 2, which is thought to have been created by spontaneous fission. TEPCO's definition didn't match the actual situation, and the company has no choice but redefine what it considers "criticality".

　二日にキセノンを検出した際、東電は「臨界の可能性がある」と発表したが、その後、検出量が少なかったことなどから「自発核分裂によるものだった」と訂正していた。

When xenon was detected on November 2, TEPCO announced "There is a possibility of criticality". However, the company corrected it as "spontaneous fission" partly because the amount of xenon detected was small.

　東電の川俣晋原子力品質・安全部長は、六日の記者会見で「再臨界かどうかでは、大変心配をおかけした。報告書の改訂版を準備している。その中で見解を示す」と述べた。

TEPCO's general manager Kawamata said in the press conference on November 6, "We're sorry we've had you worried over whether re-criticality happened or not. We are preparing the revised report, and we will elaborate on our view in that report."

　十月十七日に保安院に提出していた「中期的安全確保」に関する報告書では、キセノンなど半減期の短い希ガスが検出されないことが臨界判定基準だった。

In the report submitted to the NISA on October 17 on ensuring security in medium-term, the standard to judge the occurrence of criticality was the presence or absence of noble gas with short half life, such as xenon.

If this is true, then whoever crafted the October report to the NISA didn't know how xenon is apparently generated in spontaneous fission inside a normal reactor; and TEPCO has been operating this nuke plant for almost 40 years.

(Note to officials in Vietnam, Turkey, and India: Are you sure you want to import the Japanese nuclear power plant system?)

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#Fukushima I Nuke Plant Xenon Detection Announcement: "Wag the Dog"?

The Nuclear and Industrial Safety Agency (NISA) has now concurred (Yomiuri Shinbun 11/7/2011) with TEPCO's conclusion that it was just ordinary spontaneous fission, not re-criticality, which generated xenon gas in Reactor 2 of Fukushima I Nuclear Power Plant.

Here's a view from the supposed insider, the worker who tweets from Fukushima I Nuclear Power Plant who seems to work for one of the top-tier subcontractors.

He wonders why TEPCO announced the xenon detection when it did and strongly hinted that it was from re-criticality. I wonder the same thing, particularly when krypton-85 and xenon-131m were detected in even greater amounts in Reactor 2 Containment Vessel back in August.

From the worker's tweets on the subject:

11/3/2011 tweets:

自発核分裂のキセノンは定検中でもあることで、いつもの東電ならそこまで調べてから発表するはずなんだけど…？

Xenon from spontaneous fission is routinely detected in the regular maintenance. TEPCO normally make announcements after exhausting all possibilities.

まぁ政府や保安員にはタイムリーに伝えるけど、今まで報道発表する時はいつも調べて検討してから結果を発表してたんだよなぁ…。それが昨日に限って再臨界なんて東電が一番言いたくない表現で国民にインパクトを与え今日になって自発核分裂で安心させたのか？

They provide information to the government and the NISA in a timely manner. But when it comes to announcing to the public in the press conference, they would always investigate thoroughly before announcing. But yesterday, they shocked the public with the word "re-criticality" which TEPCO would never want to use. And today they are saying don't worry it is just spontaneous fission?

昨日の会見ではサンプリングを増やして調査に時間がかかりそうな感じだったのに、いつもなら時間をかけるのに…？まして昨日は細野大臣が1Fに来てたけど公には報道されてない。

In the yesterday's press conference [when they hinted re-criticality] it seemed like it would take long time to investigate, increasing the sampling. As they would do in normal circumstance. By the way, Minister Hosono [in charge of nuclear accident] was at the Fuku-1 plant yesterday but it was not reported in the media.

昨日あった出来事でインパクトある報道で打ち消したかったもの…？情報操作したかったもの…？

What event happened yesterday which they wanted to cover up with even more sensational news [like "re-criticality" at Fukushima I Nuke Plant]? What did they want to manipulate?

His answer to his own question is also shared by many people in Japan:

玄海原発再稼動かぁ…

Could it be the restart of Genkai Nuclear Power Plant?

Reactor 4 of Genkai Nuclear Power Plant in Saga Prefecture, which is operated by the scandal-ridden Kyushu Electric, restarted on November 2 despite strong protests and opposition in the neighboring municipalities and from all over the country. The company just did it with the approval from the pro-nuke governor of Saga Prefecture (whose father worked for Kyushu Electric) and the NISA, saying there is no need for consent from the community (Mainichi Shinbun 11/2/2011) at all.

The same vein of thinking as the petty bureaucrats in the Tokyo Metropolitan government.

But back to the xenon/krypton detection in Reactor 2 of Fuku-I Nuke Plant, not all nuclear experts are convinced of spontaneous fission, particularly those not so intimately connected with the government. I am reading what they have to say, and will report back if I can digest.

Maybe the news they wanted to cover up with a hasty declaration of re-criticality possibility and dismissal the very next day was the real re-criticality. Next time when xenon-135 is detected, no one will pay attention. "Oh it's just routine spontaneous fission, happens all the time."

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Xenon Detection in Reactor 2: Different Detection Limits on Different Days at Different Sampling Locations

Spontaneous fission, says TEPCO, the NISA says they cannot rule out criticality, and no one cares as no one believes either of them.

Here's another reason not to believe them, or take their words at face value: TEPCO tested at different locations and for different durations for the nuclides in the gas that was sucked out of the CV of Reactor 2.

Take a look at the table below, which I compiled from TEPCO's handout for the press on November 2, 2011. For each nuclide, the detected amount and the detection limit are listed for October 28, November 1, and November 2.

I was fooled when I first looked at the result of October 28, when TEPCO started the gas management system in Reactor 2. Krypton and xenon were all below detection limit. Then on November 1, they were all detected, and on November 2 xenon-133 (half life 5 days) seemingly dropped out, but other nuclides increased slightly. I thought "Something must have happened between October 28 and November 1."

That was what some reporters at the press conference on November 2 were wondering, and TEPCO's Matsumoto went along with them, not saying anything definite but hinting that the fission event was recent.

WRONG. These reporters didn't look at the fine print. (Well, neither did I...)

On October 28, the detection limits were HIGH, including those for radioactive iodine and cesium (not in the table above), indicating TEPCO didn't test long enough. That can also be inferred from the "date of sampling" information, because for October 28, no duration is indicated in the TEPCO's press handout. The nuclides may well have been in the gas on October 28 but weren't detected.

Then I also noticed that the samples were taken at different locations. On October 28, the sampling location was "gas sampling system intake"; on November 1 and 2, it was "gas sampling system dust radiation monitor".

For some unknown reason, between October 28 and November 1, someone somewhere in TEPCO seems to have decided to test longer, and at a different location. It is also possible that the dust radiation monitor was simply not ready on October 28, although I doubt that even TEPCO would start running the system before the system components were put in place and functional.

And do not be fooled that xenon-133 stopped being detected on November 2. Look at the detection limit for xenon-133 on November 1 and compare it to November 2: 10^-6 vs 10^-5. Since the amount of xenon-133 found on November 1 was in the order of 10^-6, it may well have been present in the sample on November 2, but not detected.

Here's TEPCO's handout for the press (11/2/2011):

October 28, 2011 (2nd measurement):

November 1, 2011:

November 2, 2011:

Here's the Reactor 2's gas management system overview, as released by TEPCO on October 27, 2011:

TEPCO and the Japanese government don't even know where the corium is or whether the Containment Vessel has been breached (most likely). Sucking the gas out of the Containment Vessel, which may or may not have the corium, to "reduce the amount of radioactive materials" is like trying to scoop water with a sieve.

(H/T anon reader)

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Reactor 2 CV Gas Analysis on November 2: Slight Increase in Xe-131m, Xe-135, 100-Fold Increase in Krypton-85 from November 1

TEPCO disclosed the latest result of the analysis of the gas coming from the Containment Vessel of Reactor 2 at Fukushima I Nuclear Power Plant, along with the result of the analysis done on October 28, 2011 when the gas management system started operating in Reactor 2.

There was no xenon or krypton detected on October 28. Then they were there in the analysis on November 1.

From TEPCO's handout for the press (11/2/2011), from November 1 to November 2,

• Krypton-85 (half life 10.8 years) went from 3.6 x 10^-3 to 5.3 x 10^-1, 100-fold increase

• Xenon-131m (half life 12 days) went from to 5.3 x 10^-4 to 6.1 x 10^-4

• Xenon-133 (half life 5 days) went from 6.5 x 10^-6 to below detection limit

• Xenon-135 (half life 9 hours) went from 1.3 x 10^-5 to 1.7 x 10^-5.

The unit is Bq/cubic centimeter. According to wiki, "About three atoms of krypton-85 are produced for every 1000 fissions (i.e. it has a fission yield of 0.3%)". It sure looks like a nuclear chain reaction happening, i.e. re-criticality, the possibility of which TEPCO's Matsumoto has already admitted.

The numbers for krypton and xenon are still under evaluation.

Result of November 1, 2011:

Result of November 2, 2011:

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More on Xenon Detection in Reactor 2 (TEPCO's Press Conference)

Xenon was detected in the order of 10^-5 (ten to the power of minus 5) per cubic centimeter, says TEPCO's Matsumoto in the press conference that is on-going right now in Japan. It is significant enough to conclude it is not from March. (TEPCO by the way started to netcast its press conference live, here.)

Matsumoto does think a localized, small-scale, and/or temporary nuclear fission may have occurred in Reactor 2. But not a large, sustained re-criticality, judging by the parameters (temperature, pressure, etc.).

Xenon-133's half life is 5 days, and xenon-135's half life is 9.2 hours. As to whether the amount of xenon is large or not, the company is evaluating with the help of experts.

Possibilities:

• Neutrons that exist inside the reactor hitting uranium or plutonium

• Curium-244, -242, causing "spontaneous fission"

• (I missed the third possibility that Matsumoto mentioned.)

It would be difficult to deny that the same thing is not happening in Reactors 1 and 3, says Matsumoto.

He thinks the possibility of re-criticality is low with the damaged fuel melted together with control rods and other things. Even if it does happen as the reactor is cooled further and the amount of water increases, TEPCO thinks it can be controlled by carefully monitoring the temperature and pressure.

(Reporters seem to want to reassure themselves by saying "In a nutshell, even if it is in re-criticality, TEPCO can control it, right?")

TEPCO's handout for the press on November 2, the result of gas analysis in Reactor 2 is reproduced below. The numbers are still being evaluated, says Matsumoto:

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Fuku-I Nuke Plant: Nuclear Fission in Reactor 2? Xenon-133, -135 Detected

(UPDATE: Additional information from TEPCO's press conference on November 2 in a new post.)

TEPCO poured the water with boric acid into the reactor to prevent re-criticality.

From NHK News (6:38AM JST 11/2/2011):

東京電力福島第一原子力発電所の２号機の格納容器から、核分裂反応が起きた時にできる放射性物質のキセノンが検出され、東京電力は核分裂反応が起きている可能性が否定できないとして、原子炉に核分裂反応を抑えるホウ酸水を注入しました。

Xenon has been detected in the Containment Vessel of Reactor 2 at Fukushima I Nuclear Power Plant. Xenon is created when there is nuclear fission.

福島第一原発の２号機では、先月２８日から格納容器の中から気体を吸い出し、フィルターを通して放射性物質を取り除く装置の運転を始めていて、この装置の出口付近で放射性物質の種類や濃度を測定して分析しています。その結果、１日に行った分析で、核燃料のウラン２３５が核分裂してできる放射性物質のキセノン１３３と、キセノン１３５が検出されたということです。

The gas management system has been operating since October 28 in Reactor 2 to suck out the gas from the Containment Vessel and filter out radioactive materials. TEPCO has been analyzing the gas to identify the nuclides and density. The analysis done on November 1 found xenon-133 and xenon-135, which are created when uranium-235 undergoes nuclear fission.

キセノン１３３は放射性物質の量が半分になる半減期が５日と短いため、東京電力は、再び核分裂反応が起きている可能性が否定できないとして、午前３時前から１時間にわたって原子炉に核分裂反応を抑えるホウ酸水の注入を行いました。

Xenon-133's half life is 5 days. TEPCO says it could not rule out the possibility of nuclear chain reaction happening again, so the company poured water with boric acid into the reactor to suppress the nuclear chain reaction for one hour starting 3AM [on November 2].

東京電力によりますと、原子炉の温度や圧力、それに敷地周辺の放射線量を計測しているモニタリングポストの値に大きな変動はないため、核分裂反応が起きていても規模は小さいとしています。経済産業省の原子力安全・保安院によりますと、検出されたキセノンの濃度は低く、原子炉の温度などに変化がないことから、今のところ燃料が再び溶融しているとは考えにくいとしていますが、ホウ酸水を注入したあともキセノンの検出が継続されないかどうか、状況を見極めるとしています。

According to TEPCO, there is not much change in the reactor temperature or pressure, or at the monitoring posts that measure radiation levels in and around the plant compound. Therefore, if the nuclear chain reaction is happening, it is small-scale, says the company. The Nuclear and Industrial Safety Agency says since the density of xenon detected is low and there is no change in the reactor temperature and other parameters, it is hard to imagine the fuel is melting again. But the Agency says it will monitor the situation to see if xenon continues to be detected after pouring in the water with boric acid.

Reactor 2 is where hydrogen gas concentration was rising the other day.

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