Operator Tepco has reported to regulator NISA a leak from the desalination equipment at the Fukushima Daiichi nuclear power station earlier this month, which led to around 150 litres of water containing radioactive strontium (and some caesium) draining into the sea.

The leak was discovered at approximately 11:33 on 4 December 2011 when workers found a small pool of water inside the barrier around the water desalination equipment (the evaporative condensation apparatus). The machinery was stopped within 20 minutes and leakage had ceased by 12:41.

Tepco later identified a crack in the concrete floor in the housing for evaporative concentration apparatus. Water was leaking from the crack into a gutter outside the barrier. Tepco conducted sampling surveys, which revealed that water leaking from the apparatus had flowed into the sea via the outlet of the general drainage canal. Tepco estimates that of around 240 litres of water that leaked from the housing, 150 litres flowed into the sea. So its provisional estimates put the radioactivity that found its way into the sea at 2.6 x 10^10 Bq. Tepco said that this would have ‘little influence.’

Efforts to stop the leakage included piling sandbags around the gutter. Later, around 15 cubic metres of water that had accumulated inside the barrier was pumped to a wastewater supply tank.

On 8 December Tepco submitted its report on the leakage to the Japanese regulator, the Nuclear and Industrial Safety Agency (NISA). In the report Tepco notes that it will continue to investigate the cause of the leakage, establish countermeasures and investigate the soundness of other facilities.

An inspection to determine the cause of the leakage was to be implemented by 15 December and countermeasures implemented by January 2012, the report stated. The 3A to 3C evaporative concentration apparatus will remain out of service until then.

Tepco stated that the damage, and the gap caused between the joint and concrete base, will be repaired using epoxy paint and that it is considering painting the whole surface of the concrete bottom to prevent leakage. Going forward monthly inspections of the housing will be conducted as lack of them was ‘one of the causes of the leakage’ Tepco said.

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