The Nuclear and Industrial Safety Agency (NISA) on Jan. 18 described as “appropriate” the results of stress tests on two reactors in Fukui Prefecture, its first appraisal since the nuclear accident in Fukushima Prefecture.
The Nuclear and Industrial Safety Agency (NISA) on Jan. 18 described as “appropriate” the results of stress tests on two reactors in Fukui Prefecture, its first appraisal since the nuclear accident in Fukushima Prefecture.
The administration of then Prime Minister Naoto Kan last July made stress tests a precondition to restart reactors that have undergone periodic inspections.
NISA’s appraisal was for the stress tests conducted by Kansai Electric Power Co. for the No. 3 and No. 4 reactors at its Oi nuclear power plant in Fukui Prefecture.
Kansai Electric submitted a report of its stress test on the No. 3 reactor last October. Since then, similar reports have been submitted for 14 reactors at 10 different nuclear power plants.
NISA’s appraisal will be sent to the Nuclear Safety Commission for confirmation. A final decision on whether a reactor can resume operations will be made by the prime minister and the minister of economy, trade and industry.
However, the approval of local governments will also be needed before operations can be resumed. Fukui Governor Issei Nishikawa has indicated that the stress tests alone would be insufficient for giving approval.
The electric companies’ stress test reports were expected to be submitted in autumn. But delays, including further inspections needed after errors were discovered in past data, pushed the submittal to after December for a majority of the reactors.
Meetings to hear the opinions of experts started in November. So far, those meetings have focused on the stress test reports for the Oi No. 3 and No. 4 reactors. The meeting on Jan. 18 was the seventh so far.
The meetings have covered such details as expected damage to equipment from earthquakes as well as the effects from pumping in seawater to reactor cores during emergencies. A number of experts have questioned the very process being employed, with some saying all reactors should be immediately stopped and stress tests performed.
The proposed appraisal by NISA officials was based on discussions so far.
Changes have been made in Kansai Electric’s stress test results. For example, the company said it would take about 16 days before reactor cores could no longer be cooled if all electric power sources were lost. While that was a considerable increase from the five-hour limit set by the utility before the March accident, NISA officials revised the period to seven days on grounds that equipment with weak anti-quake measures would fail to operate.
All the stress test reports submitted so far have said the reactors would be capable of withstanding quakes from 1.7 to 2 times larger than expected and surviving tsunami of 10 meters or more.
However, some reactors have only minor leeway to withstand quakes. For example, the No. 1 reactor at the Kashiwazaki-Kariwa nuclear plant in Niigata Prefecture would only be able to withstand a quake that was 1.29 times greater than expected.
Tokyo Electric Power Co., the operator of the Kashiwazaki-Kariwa plant, had to revise its expected earthquake assumptions after the Niigata Chuetsu-oki Earthquake of July 2007 exceeded what had been the expected strength at that time.
The reliability of those assumptions has again been thrown into question as a result of the Great East Japan Earthquake because the actual quake that struck the Fukushima No. 1 nuclear plant and the Onagawa nuclear plant were much larger than original assumptions.
In any event, the stress tests will continue to be the focus of attention because of the large number of reactors that have stopped operations for periodic inspections.
Of the 54 reactors in Japan, only five are still operating. Moreover, all five of those reactors will also have to undergo periodic inspection by the end of April. If no reactors resume operations, Japan would have no reactors generating electricity.
The government's energy and environment council has calculated that Kansai Electric would face up to a 25-percent electricity shortage during peak summer usage if no nuclear plants were operating. For all nine electric power companies that operate nuclear plants, there would be a total of a 7-percent electricity shortage.
The Ministry of Economy, Trade and Industry calculates that fuel costs would increase by 3 trillion yen ($39 billion) annually if all electricity generated by nuclear power was replaced by electricity generated by thermal power plants.