Tokyo Electric Power Co. (9501)’s crippled Fukushima nuclear plant faces its second typhoon season since the March 11 disaster last year, raising the risk of further radiation leaks if storms thrash exposed pools of uranium fuel rods or tanks holding contaminated water.
Typhoon Guchol hit Japan this week and moved up the main island of Honshu, prompting warnings of floods and landslides from the Japan Meteorological Agency. The Fukushima Dai-Ichi plant wasn’t damaged by the storm, which passed north of the crippled nuclear station, Tokyo Electric spokesman Taichi Okazaki said by telephone on June 21.
Typhoons rake through Japan’s islands most summers. The difference this year is Guchol arrived just a month after one of the most powerful tornadoes ever recorded in the nation hit Tsukuba, about 170 kilometers (106 miles) southwest of the Fukushima Dai-Ichi facility. The tornado, one of four to make landfall on May 6, ripped through an area 17 kilometers long and 500 meters wide, the weather agency said in a May 16 report.
The twisters killed a teenage boy, injured 50, wrecked nearly 300 houses and raised concern among scientists about tornado risk at the Fukushima plant, where explosions last year blew roofs off pools holding spent uranium fuel rods.
“Uranium spent fuel pools of No. 3 and No. 4 reactors are currently naked,” Kazuhiko Kudo, a research professor of nuclear engineering at Kyushu University, said on June 5. “A tornado with winds of 100 meters per second like the one that hit Tsukuba could suck up the pool water,” exposing the fuel rods. He raised the concern during a meeting assessing safety measures at the crippled plant in May, he said.
As dismantling and decommissioning the reactors will take decades, Tepco should review the plant’s safety measures against not only aftershocks and tsunamis but also tornadoes and huge typhoons, even if the possibility of extreme phenomena are very low, said Kudo, one of 12 members of the advisory panel to the Nuclear and Industrial Safety Agency, or NISA.
Hydrogen explosions blew off the roofs and walls of reactor buildings at the Fukushima Dai-Ichi station after the March 11 quake and tsunami disrupted power and cooling systems. There are 1,535 spent fuel rods in the cooling pool of reactor building four. Without cooling water the rods would heat up and start releasing radioactive material into the atmosphere
The utility known as Tepco hasn’t decided to install any additional safety measures against tornadoes, Junichi Matsumoto, a general manager at the utility, told reporters May 7. “It may be necessary to investigate the possibility of tornadoes in Fukushima, but we don’t plan to take any action at the moment,” Matsumoto said.
Tornadoes, which typically occur in flat lands, tend to hit coastal areas in Japan, mostly in September and October, according to the weather agency.
“It seems Japan has had more tornadoes, down bursts and flurries of winds in recent years as atmospheric conditions have destabilized,” Norio Shimoyama, a weather forecaster at the Japan Weather Association, said in an interview.
Thirty-seven tornadoes hit Japan in 2010, the most since the Meteorological Agency expanded its monitoring of them in 2007, according to the agency’s data. The U.S., about 25 times bigger than Japan, had an average of 1,253 tornadoes per year between 1991 and 2010, according to the National Climate Data Center.
A tornado strike in Fukushima could damage hundreds of tanks with contaminated water that the utility stockpiles there, Kudo said.
Much of the water injected into damaged reactors to cool melted fuel leaked into basements of plant buildings. Nearly 100,000 cubic meters of highly radioactive water is stored at the plant, according to the utility, even after Tepco used decontamination and desalination systems for about a year.
As concentrated salt water produced in the decontamination systems contains high levels of radioactive strontium, the utility keeps the processed water in tanks. About 140,000 cubic meters, enough to fill 58 Olympic-sized swimming pools, of concentrated salt water is stored at the plant, according to the utility.
Tepco plans to install a new water processing system that can remove strontium and other types of radioactive substances by the end of September and decontaminate all the salt water by September 2015, it said in a May 12 report to NISA.
“The site bristles with tanks holding radioactive water,” said Kudo, who has visited the Fukushima Dai-Ichi plant as a member of the government panel.
Tepco is trying to identify tornado risks and undertaking necessary safety measures, including construction of dams around water tanks, Shinji Obata, a Tokyo-based spokesman for the utility, said by phone. There were 858 tanks at the site as of May 30, he said.
The Fukushima nuclear plant may have released about 900,000 terabecquerels of the iodine equivalent of radioactive iodine 131 and cesium 137 into the air at the height of the disaster, Tepco said May 24. The amount is about 17 percent of the amount released at the 1986 Chernobyl accident, it said.
The utility also has had leaks of radioactive water at the plant since the disaster. About 11,000 terabecquerels of iodine 131 and 7,100 terabecquerels of cesium 134 and 137 may have leaked into the sea between March 26 and Sept. 30, Tepco said.
Tepco’s Matsumoto said he isn’t aware of any internal discussions about tornado impact. Tepco is more concerned about a building cover, he said.
Tepco completed installing a temporary cover at the No. 1 reactor building to prevent the diffusion of radioactive substances by the end of October. The cover is designed to withstand winds of 25 meters per second (56 miles per hour), Matsumoto said.
The state-owned weather agency upgraded the tornado that hit the Tsukuba area to F3, the third-strongest on the Fujita Scale Intensity Scale comprising six categories, from its initial rating of F2 on June 8. An F3 level tornado has wind speeds of 70-92 meters per second under the Fujita scale, according to the weather agency.
The wind speeds may have been over 100 meters per second in some areas, according to an on-site investigation by Yukio Tamura, a professor of architecture and wind engineering at Tokyo Polytechnic University.
“Tornadoes haven’t been assumed in designs for Japanese building for many years as the probability of one building being hit by a tornado is about once in 40,000 years in Japan,” said Tamura, who is a member of the agency’s panel to discuss ways to improve windblast forecast.
As tornadoes tend to hit coastal areas in Japan, nuclear power plants and some other structures such as liquefied natural gas terminals should have higher safety standards against strong winds, Tamura said. Typhoons sometimes accompany tornadoes, Tamura said.
“Even when a nuclear power plant is normal, pipes and power cables may be damaged by objects blown off by a tornado, which could lead to a big accident, given the Fukushima example, it should be seriously considered.”
Tepco’s executives had been informed about its own research showing the plant could be hit by a tsunami more than 10 meters high before the station was swamped by powerful waves in March 2011, it said last August. That contradicted earlier claims by top officials including former President Masataka Shimizu, who resigned after the disaster, that such a tsunami was “souteigai,” which means it was unforeseen.
“The tsunami attack wasn’t ’souteigai.’ Even though many studies warned about it, Tokyo Electric turned a deaf ear,” a commission led by Koichi Kitazawa, former chairman of the Japan Science and Technology Agency, said in its Feb. 28 report. “Speaking of ‘souteigai’ is an excuse for giving up on risk management.”
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