Dec 01

- “Now They Tell Us” Series: TEPCO Admits Reactor 1 Corium May Be 65 Centimeters into the Concrete Pedestal of Containment Vessel (EX-SKF, Nov. 30, 2011):

(UPDATE: See TEPCO’s drawing of Reactor 1 in my next post.)
(UPDATE 2: Government-commissioned research institute says “corium 2 meters into the concrete”. See my post.)

There you go! It took TEPCO only 8 and a half months to say what many people have been saying at least for 8 months.

The corium has long escaped the Reactor Pressure Vessel as admitted by TEPCO and the government. There are experts (like Hiroaki Koide) who have suggested the corium may have already left the Containment Vessel of Reactor 1, and TEPCO itself said back in May that Reactor 1 CV may have a 7-centimeter hole. Now the company says the corium may have eaten into the concrete floor of the CV to about 65-centimeter deep.

For Reactors 2 and 3, TEPCO thinks (hopes, wishes…) that a good chunk of the corium dropped from the RPV onto the CV. No mention whether the corium there is eating into the concrete or not.

From NHK News (11/30/2011; quick translation, subject to revision):

溶融燃料 相当量が格納容器に(11月30日 19:00更新)

Significant amount of melted fuel in the Containment Vessel

東京電力福島第一原子力発電所の事故で、メルトダウンが起きた1号機の燃料は、鋼鉄の原子炉の底を突き破って相当の量が格納容器に落下し、容器の底のコンクリートを溶かして最大で65センチ浸食していると推定されることが、東京電力の解析結果から分かりました。

It has been discovered by TEPCO’s analysis that the significant amount of Reactor 1’s melted fuel pierced through the steel Reactor Pressure Vessel and dropped onto the Containment Vessel, then melted the concrete at the bottom of the CV. It is estimated that the melted fuel may have eaten into the concrete to maximum 65 centimeters deep.

2号機と3号機についても一部の燃料は格納容器に落下していると推定しており、改めて事故の深刻さが浮き彫りになっています。

For Reactors 2 and 3, TEPCO also estimates that part of the fuel has dropped to the Containment Vessels, showing how severe the accident has been.

福島第一原発の1号機から3号機については、核燃料が溶け落ちるメルトダウンが起き、一部の溶けた燃料が原子炉から格納容器に落下したとみられていますが、事故から8か月以上がたっても、詳しい状況は分かっていません。

In Reactors 1 thorugh 3 of Fukushima I Nuclear Power Plant, core meltdowns have occurred, and it is considered that part of the melted fuel has dropped from the RPVs to the CVs. However, the details are not yet known even after more than 8 months since the accident started.

これについて東京電力や国内の複数の研究機関が、これまで得られた原子炉の温度や注水状況などから溶けた燃料の状態を異なる方法で解析し、30日、国が開いた研究会で結果を発表しました。

Using different methods, TEPCO and various other research institutions have been analyzing the state of the melted fuel based on the reactor temperatures and the amount of water being poured into the reactors, and the results were announced on November 30 at a workshop held by the national government.

このうち東京電力の解析では、最も厳しい評価をした場合、1号機については、すべての燃料が溶け落ち、原子炉の底を突き破って相当の量が格納容器に落下したと推定しています。

TEPCO’s result shows that, in the most severe case, all of the fuel would have melted, of which a significant portion pierced through the bottom of the Reactor Pressure Vessel and dropped onto the Containment Vessel.

格納容器の底にはコンクリートがあり、さらに鋼鉄の板で覆われています。

There is a concrete platform [pedestal] at the bottom of the Containment Vessel, which is then covered with steel plates.

燃料が格納容器の底に落ちると、高熱で反応してこのコンクリートを溶かして浸食するということで、最悪の場合、1号機で65センチの深さまで達すると推定しています。

When the melted fuel drops to the bottom of the Containment Vessel, a core-concrete reaction takes place at a high temperature, melting the concrete. In the worst case, in Reactor 1, the melted fuel could reach 65 centimeters deep into the concrete.

最もコンクリートの薄いところでは、格納容器の鋼板まで37センチしかないということで、改めて事故の深刻さが浮き彫りになっています。

At the thinnest part of the concrete, it is only 37 centimeters to the outer steel plate of the Containment Vessels. This is a very severe accident.

また、2号機と3号機についても、最悪の場合、それぞれ57%と63%の燃料が溶け落ちて、その一部が格納容器に落下したと推定しています。

TEPCO also estimates that in the worst cases for Reactors 2 and 3, 57% and 63% of the fuel have melted, respectively, and part of the fuel dropped onto the Containment Vessels.

東京電力によりますと、原子炉と格納容器の温度は、21日現在で、いずれも100度以下になっていて、溶けた燃料は水で冷却されており、コンクリートの浸食は止まっていると評価しています。

According to TEPCO, the temperatures of the RPVs and CVs as of November 21 are all below 100 degrees Celsius, the melted fuel is cooled by the water, and the erosion into the concrete has stopped.

研究会では、このほかの研究機関の解析結果も発表され、複数の結果を基に原子炉や燃料の状態について議論されました。
東京電力や国は、今回の解析結果をさらに詳しく分析し、今後の廃炉に向けて核燃料をどのように取り出すかなどについて検討することにしています。

In the workshop, the results from other research institutions were announced, and the experts discussed the conditions of the reactors and fuel based on those results. TEPCO and the national government plans to further analyze the result of the study, and determine how to remove the fuel for decommissioning the reactors.

原子力安全基盤機構、技術参与の阿部清治さんは、東京 電力の解析結果について「間違っているとは思わないが、まだ第一歩だと受け止めている。解析結果は一つだけでは答えを導き出すことができないからだ。今後 はいろいろな解析結果を積み重ねて、事故の実態を分析していく必要がある」と話しています。

Seiji Abe, technical advisor to the Japan Nuclear Energy Safety Organization (JNES) says about TEPCO’s analysis, “I don’t think it is wrong, but it is only the first step. You can’t get answers from only one analysis. We will need to understand the situation from various analyses.”

TEPCO’s presentation is posted on their site, but only in Japanese:

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_07-j.pdf

Here’s the list of documents that were presented in the workshop on November 30:

Status of the fuel core in Reactors 1 through 3:
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_09-j.pdf

Plant parameters after the accident (including data that hasn’t been disclosed so far)
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_03-j.pdf

Modification of JAEA model
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_04-j.pdf

Various approaches taken to estimate the condition of the fuel
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_05-j.pdf

MAAP analysis and core-concrete reaction
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_06-j.pdf

(You can still flip through the pages to see the charts and graphs.)

TEPCO’s drawing that indicates the thickness of the CV concrete:

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