Nuclear Experts Fear Reactor 1 Corium Not Fully-Covered With Water

#Fukushima I Nuke Plant Reactor 1 Containment Vessel May Have Only 40 Centimeters of Water, Government Researchers at JNES Say (EX-SKF, May 21, 2012):

Move over, Reactor 2 (which has 60 centimeters of water)…

Tokyo Shinbun reports that the Japan Nuclear Energy Safety Organization under the Ministry of Economy, Trade and Industry analyzed the parameters of Reactor 1 at Fukushima I Nuclear Power Plant, and concluded that there may be only 40 centimeters of water retained inside the Containment Vessel.

Tokyo Shinbun’s graphics shows the cooling water leaking from a downcomer.

The fuel debris (corium) is estimated to have eaten into the concrete floor of the Containment Vessel in Reactor 1, as announced in November last year. TEPCO’s estimate is about 65 centimeters, and the estimate by the Institute of Applied Energy is as much as 2 meters.

From Tokyo Shinbun (5/22/2012):

東 京電力福島第一原発1号機には毎時六トン前後の冷却水が注入されているのに、格納容器内の水位はわずか四十センチほどしかない可能性が、原子力安全基盤機 構(JNES)の解析で分かった。2号機の水位は約六十センチしかないことが実測で判明しており、格納容器損傷の深刻さをあらためてうかがわせた。

Analysis by the Japan Nuclear Energy Safety Organization (JNES) has revealed the possibility that the water inside the Containment Vessel of Reactor 1 may be only 40-centimeter deep, despite 6 tonnes/hour water being injected [into the Reactor Pressure Vessel]. The water level inside the Reactor 2 Containment Vessel has been measured by an actual survey to be about 60-centimeter deep. It shows how severe the damages to the Containment Vessels have really been.

解析は、注水量や格納容器への窒素の注入量と、格納容器内の圧力変化の関係を調べ、どこにどれくらいの損傷があれば、変化をうまく説明できるか探る手法を使った。

In the analysis, JNES studied the relationship between the amount of water injected, the amount of nitrogen gas injected into the Containment Vessel and change in pressure levels inside the Containment Vessel to come up with the locations and the extent of damage that would explain the change in pressure levels well.

その結果、格納容器本体と下部の圧力抑制室をつなぐ配管周辺に直径数センチの穴が開いている▽穴の場所は、格納容器のコンクリート床面から約四十センチの高さで、穴から大量に水が漏れ、水はそれより上にはない-との結論になった。

JNES has concluded that:

  • There is a hole several centimeters in diameter on the pipe that connects the Containment Vessel and the Suppression Chamber;
  • The location of the hole is about 40 centimeters from the concrete floor of the Containment Vessel.
  • The injected water is leaking from the hole in great quantities.
  • There is no water [in the Containment Vessel] above the hole.

漏れた水は、原子炉建屋地下に流れた後、配管やケーブルなどを通す穴を通じ、隣接するタービン建屋地下に流れ込んでいるとみられている。東電は1号機の格納容器の水位は約一・八メートルあると推定しているが、それより大幅に低い。

The leaked water is considered to be flowing down to the basement of the Reactor building, and then into the adjacent turbine building through the pipes and cable ducts. TEPCO has estimated the water level of the Reactor 1 Containment Vessel to be about 1.8 meters, but the JNES analysis shows it is far less.

格納容器の厚みは三センチほどあるが、穴があるとみられる配管(直径一・七五メートル)の厚みは七・五ミリと四分の一程度しかない。専門家からは、配管は構造的に弱いとの指摘が出ていた。

The Containment Vessel is about 3 centimeters thick. However, the thickness of the 1.75-meter diameter pipe that may have a hole is only 7.5 millimeters thick, or only a quarter of the thickness of the Containment Vessel. Experts have pointed out that the pipe is structurally weak.

溶け落ちた核燃料が完全に水に漬かっていないことも懸念されるが、JNESの担当者は「格納容器内の温度は三〇度程度と高くはない。水に漬かって冷やされているとみられる」と指摘する。

There is also a fear that the fuel debris [corium] may not be completely submerged in water. But the JNES researchers say, “The temperature inside the Containment Vessel is not that high, at 30 degrees Celsius. The fuel debris is considered to be submerged and cooled.”

廃炉を実現するためには、格納容器の損傷部を補修し、圧力容器ごと水没させる水棺にすることが必要。担当者は「解析結果は損傷部の特定に役立つ。今後はカメラによる実測も検討しなければならない」と話した。

In order to decommission the reactors, it is necessary to repair the damage(s) on the Containment Vessels so that the Reactor Pressure Vessel can be entombed with water. The researchers say, “The result of the analysis is useful in identifying the damage. We should also consider the actual survey using a camera.”

As I reported here in December last year, Professor Takashi Tsuruda of Akita Prefectural University, a combustion expert, thinks the Reactor 1 Suppression Chamber was damaged in the explosion.

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