Japan will drastically raise the gravity of the latest Fukushima leak to Level Three, which is considered a “serious radiation incident” on the International Nuclear Event Scale (INES) for radiological releases.

"Judging from the amount and the density of the radiation in the contaminated water that leaked...a Level Three assessment is appropriate," read the document used during Wednesday’s weekly meeting of Nuclear Regulation Authority (NRA) commissioners.

Earlier on Tuesday, TEPCO reported that another tank with highly radioactive water had leaked at the crippled Fukushima nuclear power plant. The NRA first classified the leak as a Level One "anomaly.”

The contaminated water contains an unprecedented 80 million Becquerels of radiation per liter – compared to the normal level of around 150 Bq/l.

This is considered to be the most serious setback to date for the clean-up of the worst nuclear accident since Chernobyl.

The increase to ‘Level Three’ will be formally adopted later on Wednesday after a meeting that is currently under way, a spokesman for the agency told Reuters by phone.

This is the first time Japan has issued an INES rating for Fukushima since the accident, which was caused by a massive earthquake and tsunami, took place in 2011.

The most dangerous ‘Level Seven’ has only been applied twice - for the Chernobyl catastrophe in 1986 and for the meltdown of three reactors at the Fukushima plant.

According to the International Atomic Energy Agency, each increase on the INES scale represents a 10-times increase in radiation severity.

TEPCO must keep the melted uranium fuel rods of the three destroyed reactors awash with water using a jerry-rigged system in order to keep the melted debris cool and relatively stable. To establish a closed cycle of the process, the operator stores huge amounts of radioactive water at the Fukushima plant.

It is believed that more than 350,000 tons of radioactive water is stored at the Fukushima plant in special tanks and the drainage system, without special protection in the basements of the devastated facility. At the beginning of 2013, TEPCO drained most of the basement galleries, pumping radioactive water into newly delivered tanks.

TEPCO insists that the puddle from the damaged tank has not escaped into the Pacific Ocean since the tanks are located on elevated ground some 500 meters from the seashore. However, the level of contaminated water in the tank continues to lower, the company stated.

At the same time, the ruined reactors of the Fukushima nuclear facility are located practically on the coast. And while the melted cores of the three destroyed reactors have burnt through the concrete basement of the reactor zone, radioactive water is soaking down into soil, eventually getting into the Pacific Ocean – a fact confirmed by radiation samples.

Leakage of radiation-contaminated water has been a major threat to Japan’s population and environment from the very beginning of the Fukushima disaster. But until recently, TEPCO has flatly denied that radioactive waste is escaping into the Pacific.

The company acknowledged only in late July that contaminated water is escaping from basements and trenches of the Fukushima plant into the ocean.