JNST: "A scenario of large amount of radioactive materials discharge to the air from the Unit 2 reactor in the Fukushima Daiichi NPP accident"

Journal of Nuclear Science and Technology has a paper by Fumiya Tanabe of Sociotechnical Systems Safety Research Institute published online on March 28, 2012.

Tanabe is the one who said last August that there was a second "meltdown" in Reactor 3 on March 20-21, in which the melted fuel dropped through the Reactor Pressure Vessel onto the floor of the Containment Vessel, releasing a large amount of radioactive materials that caused the spikes in radiation levels in wide areas in Tohoku and Kanto.

In November last year (11/19/2011), he also disclosed his analysis of the Reactor 2 Suppression Chamber, and concluded that it may have been damaged by the earthquake. This paper looks to be that analysis, now peer reviewed and published.

The paper was received on December 9, 2011, accepted final version for publication on January 24, 2012.

So it is possible to disclose the outline of the analysis before submitting the paper to a peer-reviewed magazine, and the magazine has no problem accepting and publishing the paper. (All those researchers in Japan and elsewhere in the world who withheld their data, analysis, research until their papers were published by peer-review magazines, what would you say now?)

From Taylor & Francis Online:

A scenario of large amount of radioactive materials discharge to the air from the Unit 2 reactor in the Fukushima Daiichi NPP accident

Fumiya Tanabe

Abstract:

Based on an analysis of the measured data with review of calculated results on the core melt accident, a scenario is investigated for large amount of radioactive materials discharge to the air from the Unit 2 reactor. The containment pressure suppression chamber (S/C) should have failed until the noon on 12 March 2011 only by seismic load due to the huge earthquake on 11 March or by combination of seismic deterioration and dynamic load due to steam flowing-in through safety relief valve. Opening of the two safety relief valves (SRVs) at 14 March 21:18 should have resulted in discharge of large amount of radioactive materials through the S/C breach with the measured air dose rate peak value of 3.130E-3Sv/h at 21:37 near the main gate of the site. The containment drywell (D/W) should have failed at 15 March 06:25, at the cable penetration seal due to high temperature caused by the fuel materials heating up on the floor of the D/W, which had flowed out from the reactor pressure vessel. Then large amount of radioactive materials should have been discharged through the D/W breach with the measured air dose rate peak value of 1.193E-2Sv/h at 15 March 9:00.

Is Tanabe saying that venting of Reactor 2 on the night of March 14, 2011, with the Suppression Chamber already broken due to the earthquake, caused a discharge of a large amount of radioactive materials through the Suppression Chamber?

What a tragi-comical sequence. Amateur hours.

If the Reactor 2 Suppression Chamber was already damaged by the earthquake, what about other Reactors?

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Japanese Researcher: "Reactor 2 Suppression Chamber May Have Been Damaged in the Earthquake"

The researcher, Fumiya Tanabe, is the same one who also said back in August that the fuel of Reactor 3 had melted twice and dropped onto the Containment Vessel.

If what he says is true that the Reactor 2's Suppression Chamber broke during the earthquake, it may have grave implications for all the other nuclear reactors in Japan with the same earthquake specifications.

Reactor 2's building exterior is pretty much intact, with only one hole on the side of the building. Yet, the NISA's estimate shows this reactor may have released more radioactive materials than the other reactors (1 and 3). If the Suppression Chamber was broken as soon as the earthquake hit on March 11, that may explain it.

From Kyodo News Japanese (11/19/2011):

東京電力福島第１原発２号機で、原子炉格納容器下部の圧力抑制プールが地震の揺れで早期に損傷したか、劣化した可能性が高いとする解析結果を１９日までに、原子力安全の専門家がまとめた。

An expert in nuclear safety complied the result of the analysis by November 19 that shows the high possibility of the Suppression Chamber of Reactor 2 at Fukushima I Nuclear Power Plant having been damaged or degraded by the earthquake.

　東電は、地震による原子炉の明らかな損傷はなく、津波による電源喪失が事故原因との立場。揺れで損傷していれば、福島第１と同様に従来の耐震基準が適用されている他の原発への影響も必至だ。東電や政府の事故調査・検証委員会の調査結果が注目される。

TEPCO still maintains its position that there was no visible damage to the reactors by the earthquake, and the cause of the accident was the loss of power because of tsunami. If the reactors were damaged by the earthquake, it would affect other nuclear power plants in Japan whose anti-earthquake standards are the same as those of Fukushima I Nuclear Power Plant. A closer look at the result of investigation by TEPCO and the fact-finding committee of the national government would be warranted.

　解析したのは日本原子力研究開発機構の元研究者で、社会技術システム安全研究所（茨城県ひたちなか市）の田辺文也所長。

The researcher who did the analysis is Fumiya Tanabe, a former researcher at the Japan Atomic Energy Agency (JAEA) and the current head of the Research Institute on Safety of Technology Systems (my translation, and not the formal name of the organization; 社会技術システム安全研究所) in Hitachinaka City in Ibaraki Prefecture.

I am trying to locate the details of his findings.

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Japanese Researcher Says Reactor 3's Fuel Melted Twice, Dropped to Containment Vessel

From Asahi Shinbun (3:02AM JST 8/8/2011; not the literal translation):

Fumiya Tanabe, former head of the research at Japan Atomic Energy Agency, will present the result of his research on Reactor 3 at Fukushima I Nuclear Power Plant in the upcoming Atomic Energy Society of Japan's conference next month.

Tanabe thinks the fuel melted and dropped to the bottom of the Reactor Pressure Vessel of Reactor 3 by March 14's explosion; then the melted fuel stayed there, cooled by more than 300-tonnes/day water. However, the amount of water injected dropped to only 24 tonnes per day from March 21 to 23, and 69 tonnes per day on March 24, probably due to increased pressure within the RPV.

It caused the melted fuel to heat up again, and the fuel melted through the RPV and dropped onto the Containment Vessel (pedestal; see the diagram from Asahi).

According to Tanabe, the amount of water from March 21 to 24 was only about 11 to 32% of what was needed to remove the decay heat, and within one day the melted fuel would attain the melting temperature again.

Tanabe thinks this massive "re-melting" caused the release of a large amount of radioactive materials into the environment which caused a spike in air radiation in wide areas of Tohoku and Kanto including Tokyo, and most of the re-melted fuel dropped from the RPV to the Containment Vessel.

The article doesn't say what Tanabe thinks has happened to the melted fuel that dropped onto the Containment Vessel since.

But the article does say this:

東電は原子炉圧力容器底部の温度が低下した状態（冷温停止）を事故収束の目標としているが、炉心の大半が溶けて格納容器に落下しているなら、収束に向けた工程表に影響する可能性もある

TEPCO hopes to have a "cold shutdown" where the temperature at the bottom of the RPV is low [below 100 degrees Celsius] as the target for winding down the nuclear accident. But if the fuel core is mostly melted and has dropped down to the Containment Vessel, it may affect the "roadmap".

No kidding. Yes it may. Where have you been, Asahi, for all these months? Is this news to you?

Tanabe's chart (from Asahi article) plotting the air radiation level (in microsieverts/hour) shows a spike on March 21. It rained that day in Tokyo.

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