The International Atomic Energy Agency (IAEA) says it had been informed that Tokyo Electric Power Company (Tepco) had discovered a water leakage at unit 2 of the Fukushima Daiichi NPP. The leak involved an estimated 25 tonnes of water from the used fuel cooling system pump room and the heat exchanger room. The leaked water flowed into a drain on the floor connected to the water collection pit (floor sump) located in a room of the first basement floor. Tepco said it had not found any leakage spread to other rooms.
As precautionary measure, Tepco stopped the used fuel primary cooling pump in order to investigate the cause and evaluated the temperature level at the pool. Tepco confirmed that the temperature was within normal range and not above around 46 degrees Celsius. This is below the 65 degrees Celsius limitation of operation. The level of accumulated water in the room had stopped rising, and it was therefore determined that the water leakage had stopped.
The leakage accumulated in the first basement floor as stagnant water. The level of water was lower than the sub-drain water level around the building, which meant the leaked water remained inside the building. Tepco said it will treat the leaked water through its water treatment facilities.
Tepco is continuing to monitor unit 2 spent fuel pool and water level, and will make an investigation into the leakage and the future countermeasure to decide on a repair plan utilising a remote control robot. IAEA said it is important to highlight that this event is not related to the treated water periodically discharged to the sea. It occurred inside the reactor building of unit 2. The Agency was not informed about any breach of radiation protection standards.
According to Tepco, an employee initially discovered that the water level of the unit 2 used fuel pool skimmer surge tank – used to confirm that the used fuel pool is full of water – had decreased. In order to investigate the cause, the primary pump for the used fuel pool cooling system was intentionally shut down.
“We will continue to monitor the unit 2 spent fuel pool (SFP) water level and its temperature and remain on standby so that we can implement SFP circulation cooling whenever necessary as we deliberate further investigations and countermeasures,” Tepco said in a subsequent statement.
“Based on field dose investigation results, we will formulate an investigation plan that utilises the remotely operated robot (SPOT),” the statement added. Tepco said it would inject filtered water into the skimmer surge tank and examine water leaking from the equipment in the fuel pool coolant cleansing system pump room/heat exchanger room. Based on the results of these investigations, countermeasures would be determined.
The used fuel pool if in the upper part of the Fukushima reactor building. During the March 2011 reactor meltdowns, hydrogen explosions occurred in units 1, 3 & 4. Unit 2 avoided such an explosion because hydrogen escaped through the partially collapsed walls of the reactor building. Tepco says currently, various strategies are being studied in preparation for removal of fuel from the unit 2 used fuel pool.
