Tokyo Electric Power Co. Holdings (Tepco), owner-operator of Japan’s Fukushima Daiichi NPP, has reported that contract workers had identified a leak of radioactive water from the water treatment system. The leak came from a pipe connected to a caesium adsorption device.

The water, used to cool the melted reactor cores in the aftermath of the 2011 nuclear disaster, is stored in around 1,000 huge tanks at the plant containing more than 1.3 million tonnes, which is now undergoing treatment dilution and eventual discharge to the sea. The water is first treated with caesium/strontium filtering equipment to remove most of the contamination. It is then treated in a multi-nuclide removal ALPS (Advanced Liquid Processing System) facility (ALPS) to remove most of the remaining radioactive materials except for tritium.

Tepco estimates that some 5.5 tonnes of water leaked from the pipe and may contain 22bn becquerels of radioactive materials, such as caesium and strontium. The water was found to be leaking from the vent opening of the second caesium adsorption device installed on the east wall of the high-temperature and high-pressure incinerator building. The vent discharges hydrogen generated within the adsorption device. The second caesium adsorption device was out of service and was undergoing flushing work with filtered water for valve inspections.

Tepco said there is a possibility that water leaked into the soil through the gaps between the metal plates under the leakage point and that as an emergency measure it will restrict access to the area and remove the soil in future.

A nearby continuous dust monitor on the premises showed a temporary slight increase in readings it subsequently returned to its original value. Tepco said there were no significant changes in the indicated values ​​of the monitoring post, site boundary continuous dust monitor, and drainage channel monitor closest to the leak point. The leak has been stopped and Tepco said the incident is being investigated and it will take measures to prevent any recurrence.

Image: The water was found to be leaking from a vent opening installed on the east wall of the incinerator building (courtesy of Tepco)