The Nuclear and Industrial Safety Agency (NISA) will start appraising the results of the first stress test conducted by a nuclear power plant under new government guidelines for a resumption of reactor operations.
The Nuclear and Industrial Safety Agency (NISA) will start appraising the results of the first stress test conducted by a nuclear power plant under new government guidelines for a resumption of reactor operations.Kansai Electric Power Co. on Oct. 28 submitted a 608-page report on the stress test at the No. 3 reactor of its Oi nuclear power plant in Fukui Prefecture.The stress tests are designed to measure the level of leeway at nuclear power plants to deal with the effects of natural disasters and other emergencies.The central government made the stress tests a condition for resuming operations at nuclear plants undergoing periodic inspections following the accident at the Fukushima No. 1 nuclear power plant.NISA's evaluation of the test results is expected to take several months.About 50 Kansai Electric employees worked for about two months to compile the results of the stress test. The report contains data on about 350 pieces of equipment at the Oi reactor.But one problem with the company's stress test is that calculations were made on the disasters as separate events. There was no calculation made of what would happen should a quake, tsunami and loss of electric power all occur at the same time."The stress test was implemented due to political considerations," Keiji Miyazaki, professor emeritus of nuclear reactor engineering at Osaka University, said. "It is only one indicator and is not always needed in terms of safety measures. It would be wrong to say nothing is wrong because a plant passed the test. Based on the lessons from Fukushima, there is a need to think about long-term measures."One part of Kansai Electric's stress test created a scenario for preventing an accident if an earthquake or tsunami much larger than forecast hit the plant. The scenario calls for using emergency generators and pumps to cool the reactor core.Computers were used to calculate the level of safety leeway against a possible quake or tsunami in each piece of equipment.The last part of the stress test involved determining the level of the quake and tsunami in which nuclear fuel in the reactor would not be damaged.The March 11 quake had a strength of 500 gal (a gal is a unit of acceleration), which was 1.26 times stronger than any quake forecast by Tokyo Electric Power Co. to hit the Fukushima No. 1 nuclear power plant. The height of the tsunami was also more than twice as high as forecast.The enormity of the quake and tsunami led to considerable damage to the nuclear fuel, causing large volumes of radioactive materials to spew into the outer environment.Calculations made by Kansai Electric in its report stated that the No. 3 reactor at the Oi plant could withstand a quake that was 1.8 times stronger than forecast and an 11.4-meter-tall tsunami, four times higher than forecast.By implementing measures after the Fukushima nuclear accident, such as adding more emergency generators and steps to prevent flooding of the reactor, safety leeway was increased by 3 percent against a quake and 145 percent against a tsunami, the company said.The stress test also calculated what would happen if all electric power sources to the reactor were lost, which is what occurred at the Fukushima No. 1 nuclear power plant.Calculations were made on the time leeway available before cooling functions for the core and spent nuclear fuel would be lost. The test found that even without outside support, the cooling system will function for 16 days for reactor cores and 10 days for spent fuel.That represented increases by 76-fold and 20-fold, respectively, compared with before the implementation of the additional safety measures, the company said.