Evaluation Status of Reactor Core Damage at Fukushima Daiichi

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Regarding the reactor core status at Units 1 to 3, we announced the following analysis results:

Concerning the Unit 1, the fuel pellets have melted, falling to the bottom of the reactor pressure vessel (RPV) at a relatively early stage after the tsunami hit the station. (announced on May 15.)

As for the Units 2 and 3, even though the (fuel) cores were partially melted, they remained within the fuel areas and the RPVs were not damaged. However, if we assume the actual water levels were lower, the analysis indicates that the RPVs were damaged. (announced on May 24)

Following the announcements, proceeding with the reactor core status evaluation, a substantial amount of data have been collected such as changes in the reactor temperature behaviors and the temperature of RPV bottom at the time of injection method and flow amount modifications including core spray system injection. Hence we have made a comprehensive review of the reactor core damage status at Units 1 to 3.

1. Evaluation status of the RPVs

1-1 MAAP analysis 【Units 1 to 3】
1-2 Heat balance evaluation per water injection records 【Units 1 to 3】
1-3 Heat balance evaluation per temperature models 【Units 2 and 3】
1-4 Evaluation per measured water levels 【Units 1 and 2】

2. Evaluation status of the Reactor Containment Vessels (RCVs)

2-1 Gas concentration evaluation of the RCVs 【Units 1 and 2】
2-2 Evaluation per Component Cooling Water System (CCWS) 【Unit 1】

3. Evaluation status per measured temperature

3-1~3-4 Evaluation per measured temperatures 【Units 1 to 3】

4. Summary

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