TEPCO has submitted a post-Fukushima stress test report for the Kashiwazaki-Kariwa nuclear power plant units 1 (BWR 5/Mark II containment) and unit 7 (ABWR/RCCV containment). It would appear that reports for units 2-6 have not been published.
TEPCO said, "In the results, we evaluated that Unit 1 and Unit 7 of Kashiwazaki-Kariwa Nuclear Power Station secured safety with some margin against earthquakes and tsunami which exceed assumption in the design. Besides, we confirmed that the safety margin [was] further improved by the emergency safety countermeasures and further safety measures."
For example, it reported unit 1 safety margins of 129% to 147% for the reactor core and spent fuel pool with respect to updated design-basis seismic ground motion (2,300 gal), and 147% and 137% for unit 7 (1,209 gal).
It said that after additional safety measures, the allowable tsunami height over the 3.3m design basis is 15m for both units 1 and 7.
It said that after additional safety measures, even if an SBO occurred, it would take about 12 days to loss of coolant injection functions for the reactor core and spent fuel pool. This length of time, TEPCO said, would be sufficient to recover off-site power or obtain support.
It said that after additional safety measures, even if the ultimate heat sink was lost, it would take 196 days before the reactor core and spent fuel pools of both units would lose heat removal function.
Additional safety measures have included water-tight seals, flood barriers, air-cooled gas turbine generators, emergency electrical switchgears, backup truck-mounted heat exchangers, installation of 18,000 m3 on-site freshwater reservoir, and underground diesel fuel tank. Other equipment installed includes a reactor building top vent, which can be opened manually by winching a wire rope from the outside, hydrogen sensors inside the reactor building, filtered containment vents, spent fuel pool water level gauge and camera, on-site heavy equipment for debris removal and additional radiation monitoring cameras.
The full reports have not been translated from Japanese into English.
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