Q&A-What do Japan's reactor stress tests mean for nuclear power?

TOKYO, July 8 Fri Jul 8, 2011 7:51am EDT

TOKYO, July 8 (Reuters) - Japan's latest attempt to dispel public wariness over nuclear safety, by calling for "stress tests" of how well they could withstand natural disasters, will likely further delay scheduled restarts of idled reactors unless the government moves quickly to give detailed procedures and schedules.

The March 11 earthquake and tsunami not only crippled the Fukushima Daiichi nuclear power plant operated by Tokyo Electric Power Co , they heightened public concerns about safety and prompted the sudden suspension of Chugoku Electric Power Co's Hamaoka plant southwest of Tokyo.

As residents balk, local governments have blocked the restart of any idled nuclear reactors since the March disaster, including several outside the disaster zone that were taken down for routine maintenance, leaving only 19 of Japan's 54 reactors in operation.

Following are questions and answers on this week's surprise call for stress tests, already under way in the European Union, and the likely impact on reactor restarts and Japan's looming power supply crunch.

Q: What are the stress tests?

They will conduct simulations, based on existing data, to gauge the resilience of reactors both to natural disasters within the realm of expectations and events exceeding that, as well as to a loss of electricity and cooling systems.

It will also take note of risk and safety assessments by similar tests on EU nuclear power plants.

Q: How long will the stress tests take?

The Nuclear and Industrial Safety Agency (NISA), Japan's nuclear watchdog, will come up with a detailed schedule within the next two weeks for conducting and announcing the results of the tests.

Unlike in the EU, all Japanese utilities have already run simulations for a "blackout" or loss of cooling functions, to meet immediate safety regulations imposed by NISA after the crisis, so an interim report could be compiled more quickly than in the EU, a NISA official said. The EU interim reports are scheduled to be completed in less than two and a half months.

Q: How do the tests differ from existing safety measures?

NISA says that recently strengthened measures have ensured the safety of Japan's reactors but the stress tests will supplement those to bolster confidence.

"This comprehensive assessment will gauge if the safety measures fulfill our requirements by 100 percent, 120 percent, or more," the NISA official said.

The government on March 30 ordered emergency safety measures such as the deployment of back-up mobile power generators, and confirmed in early May that Japan's reactors had complied.

The government nevertheless called for the Hamaoka plant 200 kilometres (120 miles) southwest of Tokyo to be shut until its tsunami defences could be strengthened further, due to government projections of an exceptionally high risk of a massive quake and tsunami hitting the area within the next several decades.

On June 7, the government ordered further enhancements to forestall atomic disasters, including securing communications and preventing hydrogen explosions, and declared on June 18 that operators had all taken appropriate measures.

Q: How will the stress tests affect reactor restarts?

It remains unclear to what extent the stress tests may delay reactor restarts, although they have complicated the process by creating uncertainty over government policy.

Trade Minister Banri Kaieda implied in comments this week that reactors had already achieved safety standards required for restarts, prior to conducting stress tests.

Asked if stress test results would become the basis for decisions to restart reactors, Kaieda told reporters on Thursday: "I believe the safety of reactors has already been confirmed ... stress tests will be conducted to further increase the sense of safety."

The announcement of the stress tests, however, prompted the mayor of the southern Japanese town of Genkai to withdraw his support for the restart of two reactors in his town operated by Kyushu Electric Power Co , which were strong candidates to become the first to restart since the March disaster. The mayor said the prime minister had suggested stress tests were a necessary condition for restarts.

Naohiro Niimura, a partner at research and consulting firm Market Risk Advisory Co, said it would be difficult to gauge the tests' impact on restarts until the government produces a schedule.

"Unless there is a clear timetable, it is difficult to forecast the prospect of restarts. Heightening uncertainty over the restarts could prompt companies to more seriously consider shifting their operations overseas," he said.

Q: Which reactors are facing delayed restarts?

Following is a list of reactors that have been shut for regular maintenance and whose restarts have been delayed or could be delayed.

-Kansai Electric Mihama No. 1 reactor: was scheduled to restart in early April.

-Kansai Electric Mihama No. 3 reactor: plans to restart in mid-July.

-Kansai Electric Ohi No. 3 reactor: was scheduled to restart in mid-June.

-Kansai Electric Takahama No. 1 reactor: was scheduled to restart in late March.

-Kyushu Electric Genkai No. 2 and No. 3 reactors: were scheduled to restart in late March and early April, respectively.

-Kyushu Electric Sendai No. 1 reactor: plans to restart in late July.

-Shikoku Electric Ikata No. 3 reactor: was scheduled to restart on July 10, but will be delayed.

-Hokkaido Electric Tomari No. 1 reactor: plans to restart early September.

-Hokuriku Electric Shika No. 1 and No. 2 reactors: no schedule for restarts due to difficulty procuring workers and necessary parts for checks after the earthquake. (Additional reporting by Risa Maeda; Editing by Edmund Klamann)