JAPAN | Restart of N-reactors still uncertain / Nuclear agency has not clarified timing, criteria for confirming safety of idled facilities

Posted on July 16, 2011


JAPAN | YOMIURI | 17 July 2011

Despite the announcement Friday of details regarding upcoming stress tests on nuclear plants nationwide, the outlook for restarting nuclear reactors remains unclear, as the final decision on whether to resume operations rests with top political leaders.

The Nuclear and Industrial Safety Agency said the first stage of the stress tests will be carried out only on nuclear reactors currently suspended for regular inspections, whereas the second stage will examine all reactors, including those in operation.

However, the agency has not specified when the tests will be conducted and completed.

The tests will check nuclear reactors through computer simulations–in contrast to periodic checkups in which equipment is actually inspected.

The first-stage assessments are expected to give the government grounds to decide whether to allow the restart of 19 nuclear reactors that are currently suspended for regular inspections. However, the standards for deciding whether to resume operations at those reactors have not been clarified.

“All the reactors are safe. The first-stage assessments are just to relieve public anxiety about restarts,” said Tomoho Yamada, director of the agency’s Nuclear Power Licensing Division.

“Based on the results of the assessments, political leaders will judge if it’s safe [to restart the reactors],” Yamada said.

At a press conference Friday, Goshi Hosono, state minister for conclusion of the nuclear incident, said only, “Four [concerned ministers], including the prime minister, will make a final decision after hearing the opinions of the NISA and the Nuclear Safety Commission.”

But it is unclear how they will interpret the results of the first-stage assessments.

The first stage will examine nuclear reactors to determine the “margin of safety” for their important safety facilities–such as piping, pumps and control rod drive systems.

For example, if equipment that can withstand temperatures of up to 500 C is placed in a location for which the maximum allowable temperature is 300 C, the equipment would be judged as having a 200 C margin of safety.

According to the agency, each reactor has more than 100 kinds of equipment to be tested in the first stage. Each electric company is expected to first confirm the margin of safety for each type of equipment, and then investigate what damage a reactor core might suffer in an earthquake and other disasters.

The second-stage assessments will be carried out, in principle, on nuclear reactors now in operation. Reactors will be checked as to what extent they can maintain safety amid disasters of unexpected proportions.

By using computers to simulate earthquakes and tsunami that create conditions far in excess of safety standards, electric companies will determine in the second stage what severity of conditions would damage pumps and piping, and ultimately lead to core damage.

By ascertaining the weak points that could trigger severe accidents, the government hopes the second-stage assessment will help improve safety measures.

Both the first- and second-stage assessments will be conducted on the supposition of a natural disaster such as an earthquake and tsunami. The stress tests also will simulate blackouts and loss of cooling functions at nuclear power plants.

When the draft of the stress tests was presented at the Nuclear Safety Commission on Friday, a member of the commission complained: “It’s hard to understand the content of the assessments. If this isn’t resolved, electric companies won’t understand what to do, and the public won’t understand either.”

The NSC, which created a rough outline of the stress tests, plans to submit the draft to the NISA as early as this week and present documents ordering electric companies to carry out the tests after obtaining the agency’s approval.

However, it is not clear when the first-stage assessments will be completed and the idled reactors allowed to restart.

Stress tests were introduced in European nations after the outbreak of the crisis at the Fukushima No. 1 nuclear power plant. Last month, a ministerial meeting of the International Atomic Energy Agency said all countries with nuclear power plants should check the safety of their reactors.

The agency drew up the first- and second-stage assessments based on European countries’ tests.

The second-stage assessment is similar to the European stress test, which takes about five months to complete.

The first-stage assessments will be on a smaller scale and examine fewer items than the second stage. By simplifying the first-stage assessments, the government plans to restart the reactors earlier.

“I think we can obtain results in less than five months,” Yamada said.

However, Hosono did not clarify the schedule of the stress tests, saying, “We want the NISA and the NSC to proceed with the operations swiftly, but it’s not good to rush them.”

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