Japan's Ohi 3 station submits stress test results

8 November 2011

Japanese utility Kansai Electric Power Co has reported to Japan's Nuclear and Industrial Safety Agency that its 1200MWe-class Ohi 3 PWR has a sufficient safety margin to withstand beyond-design scenarios.

The utility is the first to report results of its own post-Fukushima stress tests, which were mandated by the Japanese regulator, but which NEI magazine understands are not detailed.

According to an English-language summary published by Japan Atomic Industrial Forum's Atoms In Japan news service, the utility performed a computer simulation of beyond-design-basis scenarios based on Fukushima Daiichi lessons. In case of earthquakes followed by a tsunami, margins against reactor core damage take into account safety measures for the entire facility, and measures that protect fuel from severe damage.

Most Japanese reactors currently remain offline in periodic inspection outages, pending post-Fukushima review.

Kansai EPCO calculated the safety margins of individual pieces of equipment in the case of an earthquake where fuel damage might occur due to equipment damage from beyond-design-basis seismic forces. It showed that Ohi 3 could withstand an earthquake 1.8 times the standard intensity.

Kansai EPCO concluded that safety measures at the plant have improved 145% compared with before March 2011. In the event of loss of all AC power, the reactor core can be cooled for about 16 days without external assistance; an increase of a factor of 76 compared with before March. Kansai EPCO used knowledge of the Fukushima Daiichi incident to develop multiple methods for cooling the core.

JAIF said that the Japanese regulator will integrate assessments from all utilities, conduct hearings, consult with the Japan Nuclear Safety Commission, and hold an international seminar in November 2011.

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