Ohi 3 completes initial stress test

31 October 2011

Kansai Electric Power Company (Kepco) announced that unit 3 of its Ohi nuclear power plant had completed the first part of the two-step stress tests stipulated by the Japanese government.


Ohi (Kepco)
The four-unit Ohi plant (Image: Kepco)
In response to the accident at the Fukushima Daiichi plant following the natural disasters, the Japanese government ordered all 35 reactors that had been shut down for regular safety inspections to remain offline. In addition, units subsequently entering such inspections would also have to remain shutdown until given permission to restart.


In July, the Japanese government said that Japanese reactors would be subjected to stress tests to be conducted in two phases. Step one will be applied to those reactors which have been taken offline for periodic inspections to determine whether they could withstand large earthquakes and tsunamis. Under this step, utilities are required to examine the safety margin of important pieces of equipment in accordance with guidelines to be set by the country's Nuclear and Industrial Safety Agency (NISA) and Nuclear Safety Commission (NSC). Based on the results of these initial tests, the government will decide whether a reactor shut for inspections can or cannot resume operation.


Step two will involve a comprehensive safety assessment of all reactors and will be conducted to enhance the reliability of safety checks. These tests will be similar to the stress tests proposed by the European Union.


Kepco announced on 28 October that it had submitted a report to NISA, Fukui prefecture and Ohi town giving the results of the initial step of these stress tests at Ohi 3. The company said that the results show that there are sufficient safety margins in the design basis of significant facilities and equipment for the unit to survive large earthquakes and tsunamis. Furthermore, countermeasures taken since the Fukushima Daiichi accident have increased those safety margins.


According to Kepco, Ohi 3 - a 1180 MWe pressurized water reactor - would be able to withstand an earthquake with ground acceleration of up to 1260 gal (1.8 times its design basis of 700 gal) and a tsunami 11.4 metres in height (four times its design basis). In addition, should the unit lose all off-site power supply, the reactor could still be kept cool for up to 16 days through the use of fire engines pumping water, while the used fuel pool could be cooled for up to 10 days.


NISA will now examine the results and then pass them on to the NSC for consideration. The decision to allow Ohi 3 will then be taken by Prime Minister Yoshihiko Noda; minister for the economy, trade and industry Yukio Edano; minister for conclusion of the nuclear disaster Goshi Hosono; and chief cabinet secretary Osamu Fujimura.


Edano was quoted by the Daily Yomiuri as saying, "We'll make a political decision on whether to allow the resumption of operations after taking into consideration whether local residents and the general public agree to and understand the restart."


As of 15 October, just ten of Japan's 54 power reactors were in operation, according to data released by the Japan Atomic Industry Forum. This represents 8684 MWe, or 18%, of the country's total nuclear generating capacity of 48,960 MWe. Thirty-one units, with a combined generating capacity of 26,383 MWe are not operating as they have been shut for periodic inspection, while another unit has been shut for unplanned inspections or equipment replacement.


Researched and written

by World Nuclear News