Important Report from TEPCO

The Tokyo Electric Power Company, Incorporated, would like to make comments on subjects that are reported by the newspapers, TV or websites.

We reaffirmed the seismic safety of Unit 4 Reactor Building.

Jun 29, 2012

1.Regarding the exterior wall of Unit 4 Reactor Building, TEPCO has been conducting 3 additional investigations, since confirming a partial expansion on the 3rd floor west wall (result previously announced on May 25, 2012). The 3 investigations include detailed scale measurement, concrete strength verification and the visual inspection of the exterior wall.

2.The investigation results were as follows. First, the scale of the partial expansion was negligible compared to the whole exterior wall. Second, the concrete strength was 1.5 times larger than the design standard. Third, by visual inspection, no crack of which the width exceeds 1mm was confirmed. Consequently, the overall seismic safety of the Unit 4 Reactor Building is judged to be ensured, even taking into account the partial expansion at the 3rd floor west wall. The partial expansion is assumed to have generated by the force of explosion, at the time of the building explosion which occurred on March 15, 2011. A well for machinery hatches and elevator shafts pierces through the 1st to the 5th floor at the interior of the concerned wall. This well which weakens the force constraints from the floor slab, is assumed to be a cause of this phenomenon.

3.To make sure, we conducted a Seismic Response Analysis*1 under a condition that the concerned wall possesses no bearing force, and using the Basic Earthquake Ground Motion*2 "Ss", which is the same scale as the Tohoku - Pacific Ocean Earthquake. As a result, both the Reactor Building and the Spent Fuel Pool were confirmed to have sufficient amount of safety allowance compared to the design standard.

4.The Spent Fuel Pool itself is made of reinforced concrete that has a thickness of approx. 140-185 cm. It is supported by the floors and the walls under the pool to the building base, and the exterior walls above the 3rd floor hardly contribute to the support. Therefore, the pool is not affected by the partial expansion.

*1 Seismic Response Analysis is an analysis that specifies the degree of deformation impact on facilities.

*2 Basic Earthquake Ground Motion is a scale of a shake under the plant calculated upon the input of the supposed largest earthquake that is probable to occur around the plant. Unit is "gal". "1 gal" is equivalent to accelerating 1 cm per second.

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