Four tons of possibly contaminated rainwater has leaked during a transfer of radioactive water between tank holding areas at Fukushima, the operator of disaster stricken Japan’s nuclear plant said.

A spokesman for Tokyo Electric Power Co (TEPCO) said heavy rain during a recent typhoon has flooded one of the tank holding areas. It stores excess water which has been flushed over damaged reactors to keep them cool, Reuters reports. 

After tests last month showed the rainwater contained 160 becquerels per liter of radiation, a relatively low level, the Fukushima operator decided to transfer the water to another holding area for tanks, he said. 

One of the workers found the leak during the transfer, with the water being absorbed into the ground. TEPCO estimated the amount of leaked water at around 4 tons, the spokesman added. 

The company has been pumping hundreds of tons of water on a daily basis over the Fukushima reactors to keep them cool, with radioactive wastewater then being stored in underground tanks. 

In August, TEPCO said at least one of those hastily built tanks has leaked around 300 tons of radioactive water. High levels of radiation were also found just above the ground, suggesting widespread structural problems with the tanks. 

Fukushima is likely to face more heavy rain in the next few days, with another storm expected to hit Japan on Wednesday, the forecast by US Navy Joint Typhoon Warning Center said. 

Reuters / Pool

Meanwhile, South Korean Minister of Oceans and Fisheries Yoon Jin-sook has slammed Japan and TEPCO for earlier attempts to downplay and cover up the facts of contaminated water leaks at the crippled nuclear facility. 

She said Tokyo’s “absurd” actions have affected the South Korean fishermen, adding that it was the country’s duty to inform its neighbors that it was planning to contaminate the ocean by releasing hundreds of tons of radioactive water into it. 

“We wondered if we had to protect such immoral people under diplomatic protocols, and so we did it [by placing an import ban on Japanese fishery products] as soon as we could,” Yoon is cited as saying by Japanese Daily Press. “We did not know that Japan would let the contaminated water leak. We thought ‘this cannot be allowed while our people’s fears were growing.’” 

In September, South Korea has introduced an import ban on all fishery products from eight Japanese prefectures near Fukushima due to possible health risks to the country’s consumers. 

TEPCO had recently reversed its denials and confirmed reports that Fukushima is leaking radioactive water into the Pacific Ocean. The operator plans to allocate around $500 million towards purifying the radioactive water and freezing the soil around the station in order to cope with the leaks. 

The Fukushima plant has suffered triple nuclear meltdowns and hydrogen explosions since it was hit by an earthquake, followed by a tsunami, in March 2011.