Tokyo Electric Power Co. must speed up plans to cover reactors at its crippled nuclear plant and drain tainted water to prevent more radiation leaks as Japan’s typhoon season approaches, engineering professors said.
In 2004, eight cyclones passed over or skirted Japan’s Tohoku region, where the Fukushima Dai-Ichi power station is spewing radiation after an earthquake and tsunami on March 11. The earliest was in May that year, according to Japan’s weather agency data. The eyes of two storms passed within 300 kilometers (180 miles) of Tohoku last year, the data show.
Last month’s disaster wrecked the plant’s cooling systems, triggering the worst nuclear crisis since Chernobyl in 1986. The roofs of three buildings were damaged in blasts as water inside reactor cores and spent-fuel ponds boiled away. The utility known as Tepco plans to install temporary covers within nine months, and concrete ceilings over the “medium term.”
“The buildings should be covered at least before the typhoon season is in full swing by late July,” said Tadashi Narabayashi, a professor of nuclear engineering at Hokkaido University. “Tepco’s actions are like a game of Whack-a-Mole because the company keeps reacting after the event.”
Tepco said on April 17 it will start erecting temporary covers for the damaged building within three months provided radiation falls to levels at which workers can begin construction. The work is expected to be completed in the next three to six months, according to the action plan, which lists the “possibility of the cover being damaged by a big typhoon” as a risk.
The company hasn’t decided what material it will use to temporarily cover the buildings, Tepco spokesman Hajime Motojuku said today.
The covers are the only measures planned at the moment to protect against typhoons, Takeo Iwamoto, a Tepco spokesman, said yesterday. The company may install them faster than the plan announced on April 17, he said.
The Japan Meteorological Agency doesn’t make forecasts for how many tropical storms or typhoons are expected to approach the country, Hajime Takayama, a weather forecaster at the bureau, said by telephone.
“It’s quite possible for a typhoon to hit the Tohoku region while maintaining its strength, although most tend to make landfall in the south,” Takayama said.
Typhoon Melor smashed into Japan west of Tokyo in October 2009, leaving five people dead. The storm weakened as its eye passed over land to the west of the Fukushima station, where it dumped more than 30 millimeters (1.2 inches) of rain per hour in the early hours of Oct. 8, 2009, according to the JMA.
Tepco shares fell 5 percent to 423 yen in Tokyo. They are down almost 80 percent since the disaster.
The Fukushima plant, 220 kilometers north of Tokyo, has six reactors, three of which were shut for maintenance when the earthquake and tsunami struck, leaving almost 28,000 people dead or missing.
Reactor buildings weakened by explosions may suffer further damage if a typhoon hits them, while strong winds and rain could scatter radioactive materials and water, said Hironobu Unesaki, a nuclear engineering professor at Kyoto University.
Tepco has been pouring millions of liters of water to cool the reactors and spent fuel after the accident, which has flooded basements and trenches near the buildings that house them. Some highly contaminated water leaked into the sea and the utility has dumped less-toxic fluids into the ocean.
About 520,000 liters (137,000 gallons) of water with a level of radioactivity that was 20,000 times the legal limit leaked into the ocean between April 1 and 6, Junichi Matsumoto, a Tepco general manager, said today at a briefing in the Japanese capital.
The amount of radiation discharged in the leakage was 4,700 terabecquerels of iodine-131, cesium-137 and cesium-134, according to a statement from Tepco.
Basements and trenches around the reactor buildings are also flooded with radioactive water, preventing repairs to the electrical equipment and cooling systems.
“Heavy rain may cause radioactive materials to soak further into the ground and enter the water table," Unesaki said. ‘‘This could affect drinking water.’’
Tepco started pumping contaminated water out of trenches near one of the reactor buildings that were damaged by the blasts, Matsumoto said on April 19. The company aims to move 10 million liters of the contaminated water to a storage unit and expects to complete the transfer in 26 days.
About 450,000 liters was pumped out by 7 a.m. today, spokesman Takashi Kurita said at the briefing in Tokyo today.
‘‘It will be too late to start preparations once a typhoon approaches,’’ said Narabayashi of Hokkaido University. ‘‘It’s a basic risk principle that you proactively take measures against circumstances that are predictable.’’
Radiation in excess of 100 microsieverts per hour was measured at 2 kilometers away from the nuclear plant on April 18, Japan’s science ministry said today.
Japan’s government imposed a 20-kilometer (12 mile) no-entry zone around the crippled plant in the interests of public health, Chief Cabinet Secretary Yukio Edano said today.
The order will go into effect at midnight today, Edano said at a press conference in Tokyo. An earlier directive asking about 80,000 residents living within the radius to evacuate wasn’t legally binding.
Some have returned to the area to collect belongs and check their properties against the advice of officials. One person per household will be allowed to return to their homes for two-hour periods to retrieve possessions, Edano said.
‘‘There has been a strong desire from evacuees who left without anything to go back,” Edano said. Groups will be transported by bus and required to wear protective gear, he said.