A water recycling system at Japan's damaged nuclear power plant was halted for repairs Monday after a brief run that had been hailed as major progress in restoring control and improving conditions at the crippled plant.
Tons of fresh water has been pumped to the plant to cool its reactors, a process that taints the water with radiation. About 110,000 tons of tainted water has accumulated and could overflow by early July if the recycling system fails or other storage options are not enough.
Workers have struggled for weeks to use a new system to clean the tainted water and reuse it in the cooling process. The water treatment components fully operated for five hours earlier this month, and test-runs were conducted before it went fully operational Monday. It also pumped treated water into the reactors _ a long-awaited new phase that lasted only briefly.
Plant operator Tokyo Electric Power Co. said the recycling system was halted about an hour and a half after it began operating. Workers spotted water leaking from a hose that was sending the processed water into the reactors, TEPCO spokesman Junichi Matsumoto said.
The leak shut down the recycling segment of the system, while the cleaning segment is continuing to operate. Workers switched back to fresh water injection into the reactors, Matsumoto said.
No new leakage outside the plant has been reported. TEPCO plans to start repair work early Tuesday to restore the recycling segment as soon as possible, hopefully by the end of the day.
The multinational system has reprocessed 1,850 tons of contaminated water as coolant to be pumped back into the reactors. In full capacity, the system can treat up to 1,200 tons of contaminated water per day, more than twice as much as needed to cool the three reactors.
The March earthquake and tsunami destroyed power and cooling systems at the Fukushima Dai-ichi plant, melting reactor cores and leaking massive amount of radiation. Some contaminated water seeped into the ocean in April and May, causing criticism and concerns in and outside of Japan.
Some of the tainted water is stored in temporary tanks, but the rest has still pooled inside reactor and turbine basements and utility pits, hampering workers and risking radiation exposure.
TEPCO has sealed cracks, set up oil fences around the coastal plant, and acquired more storage tanks in case of emergency. But as long as the cleaning segment of the recycling system is functioning, the volume of tainted water will not grow.
Announcing the launch of the recycling system earlier Monday, Goshi Hosono, newly appointed nuclear crisis minister, called the system "a major step forward" toward stable cooling of the reactors. But he said he was not fully confident about the system.
"It's a problem if the system continues to be unreliable," he said. "We must turn it into something that can feed water stably."
TEPCO and the government have said they hope to achieve a cold shutdown of the reactors by January by bringing the core temperatures to below 100 Celsius (212 Fahrenheit).