A leak of radioactive water was found in the piping of water used to cool the spent fuel pool in the undamaged No. 5 reactor building of the Fukushima No. 1 nuclear power plant, its operator said on July 19, a sign of possible deterioration in the system.
Tokyo Electric Power Co. said water from the cooling pond leaked, citing comparable levels of the concentration of radioactive substances in the leak and the pool.
A TEPCO employee found a pool of water in each of two boxes–75 centimeters by 50 cm–that house a control valve in the cooling water piping system on the fifth floor of the No. 5 reactor building at 1:25 a.m. on July 19.
The water had collected to a depth of 9 cm in one box and 18 cm in the other.
The water contained 2-3 becquerels of cobalt 60 per cubic centimeter, according to the utility.
The Unit 5 and 6 reactors were not in service at the time of the March 11, 2011, earthquake and tsunami. Both reactors were fueled at the time of the accident. The Unit 4 reactor was out of service at that time, which all its fuel transferred to its spent fuel pool.
The problems at Unit 5 are ongoing, and point out limits on the efficacy of previous inspections:
Experts say the continuing leaks indicate that valves are deteriorating, and that the utility’s inspections are inadequate.
“We are aware that our approach proved to be lax as we were unable to detect the problem until the leak occurred,” a TEPCO official said. “We are reviewing the way checks should be conducted.”