FUKUSHIMA — Rainwater containing radioactive contaminants flowed from a drainage ditch by the reactor buildings at the Fukushima No. 1 Nuclear Power Plant into the sea on five occasions in just over four months, it has been learned.
The ditch is 2 meters deep and 2 meters wide, and stretches for about 800 meters. It was created to ferry rainwater from the plant grounds into the ocean, but in February this year it was learned that highly contaminated rainwater from the top of the No. 2 reactor building had flowed into the ditch and subsequently into the ocean. Tokyo Electric Power Co. (TEPCO), the operator of the plant, set up a 70-centimeter-high dam in the ditch, as well as eight pumps to move water from the ditch to another ditch that runs into a sealed harbor area. The pumps, which together can process rainfall of 14 millimeters per hour, were started on April 17 this year.
On April 21, however, loss of power caused by trouble with power generators resulted in all of the pumps shutting down, and contaminated water leaked into the sea. On July 16, rainfall rose to 21 millimeters per hour at one point. This was more than the pumps could handle, and workers confirmed that water flowed into the ocean. In all, five leaks from the ditch occurred in the period between April 17 and Aug. 27.
The concentrations of radioactive cesium and other radioactive materials in the contaminated rainwater ranged from around 20 to 670 times the safety level set for a “subdrain” plan in which decontaminated groundwater is to be released into the ocean.
The volume of leaked rainwater is unknown, but no changes have been seen in radioactive concentrations in the sea near the plant.
The Fukushima Prefectural Government on Aug. 27 issued a new request to TEPCO to introduce leak prevention measures. The next day, TEPCO raised the ditch dam by 15 centimeters, but Naohiro Masuda, chief decommissioning officer at Fukushima Daiichi Decontamination and Decommissioning Engineering Co., says, “Our main countermeasure will be to replace the ditch with a new one.”
This new ditch is designed to carry rainwater into the sealed harbor area. Masuda indicated that until completion of the new ditch — scheduled within the fiscal year — additional leaks may be unavoidable. The plant therefore looks set to enter the typhoon season without full preparations against further leaks.
In February, after the rainwater leaks were discovered, fishermen protested that TEPCO had not released radiation measurements for the drainage ditch water for around 10 months. Negotiations with fishermen over the subdrain plan were subsequently put on hold. However, the Fukushima Prefectural Federation of Fisheries Co-operative Associations officially agreed to the plan after receiving notification from TEPCO and the national government regarding measures to prevent a recurrence of the leaks.
Regarding the rainwater leaks, federation chairman Tetsu Nozaki commented, “All we can do is to ask TEPCO to improve the situation. The subdrain plan is a separate issue, and there is no change in our acceptance of it.”