4 Octobre 2013
October 4, 2013
Patience is wearing thin over Tokyo Electric Power Co.’s continuing series of blunders at the stricken Fukushima No. 1 nuclear plant, the latest one allowing more radioactive water to spill into the ocean.
Katsuhiko Ikeda, secretary-general of the Nuclear Regulation Authority, summoned TEPCO President Naomi Hirose on Oct. 4 and demanded a plan to deal with the contaminated water problem at the plant. Ikeda said effective measures must be taken, even if it involves bringing in personnel from TEPCO’s other nuclear plants, including the one it plans to restart in Niigata Prefecture.
“Problems have been caused by basic mistakes,” Ikeda said. “They will recur unless appropriate site control measures are taken.”
Hirose said his utility will do its best to deal with the issue.
The Fukushima prefectural government on Oct. 3 asked Yoshiyuki Ishizaki, head of TEPCO’s Fukushima Revitalization Headquarters, to ensure that no more radioactive water escapes from the hundreds of storage tanks at the site.
Ishizaki apologized and admitted to TEPCO errors in its assumptions and flaws in its control measures.
The latest leak of radioactive water into the ocean was caused by a combination of problems: an overpumping of rainwater into a storage tank due to a mistake in properly monitoring water levels, and an ill-arranged measure to ensure early discovery of radioactive water leaks.
The leak occurred on Oct. 2 as rainwater from an approaching typhoon threatened to fill and breach a barrier surrounding five storage tanks connected by pipes in the B-South area of the plant.
Workers decided to transfer the rainwater into the tanks, each with a capacity of 450 tons, until they were 98 percent full.
The ground where the five tanks sit is inclined toward the sea.
The only water gauge was mounted on the highest tank on the hill side.
The workers used that water gauge to monitor the water levels in the other lower tanks. It took them a while before they realized that water had reached the top of the tank at the lowest level on the sea side.
“We believed it was a narrowly safe level,” Masayuki Ono, acting general manager of TEPCO’s Nuclear Power and Plant Siting Division, told a news conference on Oct. 3.
They were wrong.
The water reached the top of the sea-side tank and spilled out as the rainwater continued to be pumped in.
TEPCO said it had never expected to fill the storage tanks near their capacity and thought it was safe to build such tanks as long as the ground incline did not exceed 1 percent.
The water in the tanks contained 580,000 becquerels of beta ray sources, such as radioactive strontium, per liter. The water pooling inside the barrier showed 200,000 becquerels per liter when TEPCO made the measurement on the afternoon of Oct. 2.
These figures indicate considerable amounts of radioactive water leaked from the tank into the interior of the barrier.
TEPCO officials said the leak may have started immediately after the pumping began and continued for up to 12 hours.
Radioactive water also dripped outside the barrier by way of scaffolding mounted on the tank. Part of that water likely entered a drainage ditch and flowed into the sea, TEPCO officials said.
Rainwater accumulated in the barrier because of a measure TEPCO took following the August discovery that 300 tons of highly radioactive water had leaked from a tank and breached a barrier in a separate area on the site. Some of that water eventually reached the ocean.
Until August, TEPCO workers kept the drainage valves on barriers permanently open to prevent rainwater from forming pools around tanks and making it difficult to immediately spot radioactive water leaks.
Because of that precaution, highly radioactive water that escaped the tank did leak unnoticed via drainage valves to the exterior of a barrier.
The NRA ordered TEPCO to keep the drainage valves shut and to pump water pooling inside barriers into the storage tanks.
But with the valves closed, TEPCO was forced to do something with the rainwater filling the barrier. The rainwater is supposed to be kept under control as potentially radioactive water.
TEPCO calculated that water would overflow barriers during a rainfall of 120 millimeters or more, a downpour that it believed occurs once or so a year, company officials explained.
When another typhoon approached on Sept. 15, water overflowed the barrier surrounding the B-South area--the site of the Oct. 2 leak. TEPCO workers collected 1,400 tons of water during that typhoon.
TEPCO hopes to check the radioactive levels of the rainwater once it has been transferred into temporary storage tanks, and release it into the sea if its levels are low. But the NRA has yet to approve that plan, citing flaws in TEPCO’s measurement methods and standards for discharging waste into the environment.
The company said it plans to heighten the barriers to cope with the water situation, adding that the work will be completed at the end of this year.
TEPCO’s Ishizaki told the prefectural government that the utility will install water gauges before the end of November on all storage tanks that are of the same type as the source of the latest leak.
(Ryuta Koike contributed to this article.)