The Tokyo Electric Power Company has said it has found radioactive hotspots near tanks holding waste water from the stricken Fukushima nuclear power plant.
It was revealed earlier this week that up to 300 tonnes of radioactive water have leaked from a containment vessel.
But Tepco maintains it has not seen any change in the levels of radioactivity in the Pacific.
The leak runs into the sea from a ditch about 50 metres from the tank and that is where the radioactivity has been detected.
The Japanese Nuclear Regulator, said this calls into question the structural integrity of other tanks.
The regulator’s head, Shunichi Tanaka, said: “I don’t think it’s a single tank. If a leak occurred in one tank, we should assume that the same thing could happen at other tanks as well, and come up with measures to deal with it.”
The tsunami from an earthquake in 2011 knocked out the cooling systems in the plant.
That caused fuel rods to overheat, leading to an explosion and the meltdown of three reactors, which in turn meant radioactive contamination of sea, air and land.
Nearly 200,000 people had to be evacuated in the world’s worst nuclear accident since Chernobyl in 1986.
The company is keeping the reactors cool with water, meaning every day an extra 400 tonnes of radioactive water needs to be contained. That is the equivalent of an Olympic swimming pool every 10 days.
In order to keep up with the rate at which the water is being accumulated, Tepco has been building tanks with plastic seals and it is believed the leaks are coming from these seals. There are 350 tanks of that design on the site.
The radiation level needs to be kept in perspective. It is estimated to be between a tenth and a third of that from Chernobyl.
But there is a potential health risk for the local population.
Results of medical check-ups performed on those aged 18 or younger at the time of the disaster have found 18 have thyroid cancer. It is suspected in 25 others. Another 150,000 youngsters are still be examined.