Efforts to clean up the mess at the Fukushima No. 1 nuclear power plant suffered a setback June 16 when a new water purification plant designed to scrub highly radioactive water sprung a leak during a test.
Efforts to clean up the mess at the Fukushima No. 1 nuclear power plant suffered a setback June 16 when a new water purification plant designed to scrub highly radioactive water sprung a leak during a test.
Tokyo Electric Power Co., the plant's operator, said the plant detected the leak and shut down automatically.
The leak occurred when a high-pressure safety valve ruptured on a cesium adsorption device, TEPCO said June 17.
The utility said it expected to install replacement parts and have the plant fully operational by midnight.
Key components of the purification plant are four chained cylindrical adsorption devices. Filled with zeolite, a cesium-adsorbing mineral, they are about 90 centimeters in diameter and 2.3 meters high.
An alarm went off and the equipment shut down at 7:20 p.m. on June 16.
Around 8 p.m., a worker found that the metal housing around the devices was filled with about 30 centimeters of water.
Radioactive water also leaked outside the casing.
During the test using low-level radioactive water, pressure soared in the adsorber and the safety valve ruptured as designed, allowing water to escape.
A valve on a pipe linking the adsorber to the next one in the chain was found in the closed position, leaving the water with nowhere to go and causing the rise in pressure in the first adsorber, TEPCO said.
A worker may have mistakenly left the valve handle in the closed position, the utility said.
At least 6,000 liters of water leaked, but the radiation level was low--less than 10 microsieverts per hour, TEPCO said.
TEPCO planned to replace the safety valves on the three remaining adsorption devices. Test runs were started at dawn July 17 for all purification devices other than the cesium adsorbers.
The purification plant plays a central role in the "cyclic injection of cooling water" as detailed in the timetable released by TEPCO in May.
About 500 tons of water continues to be pumped in daily to cool down the nuclear reactors. Radioactive water, contaminated through direct contact with damaged fuel rods, is seeping into basements.
Receptacles to contain the water, including the condenser at the No. 1 reactor, have only a remaining capacity of 2,200 tons. There is the risk of water leaking outside or into the ground if the operation of the purification facility is delayed.
(This article was compiled from reports by Naoya Kon, Harufumi Mori and Hiroshi Ishizuka.)