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):

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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.

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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.

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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.

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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.

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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.

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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.”

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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.