Japanese Government officials have not figured out what to do with more than 1 million tonnes of radioactive water sitting at the site of the crippled Fukushima nuclear power plant.

Key points: The rate of contaminated water reaching the facility has slowed, but is still increasing

The rate of contaminated water reaching the facility has slowed, but is still increasing There are now more than 1,000 tanks of contaminated water at the site

There are now more than 1,000 tanks of contaminated water at the site One controversial option for dealing with the water includes decontaminating it as much as possible and then gradually releasing it into the ocean

Just days shy of the seventh anniversary of the nuclear disaster, Tokyo Electric Power Company (TEPCO) revealed it successfully slowed the rate of contaminated water reaching the reactor facilities, but the amount was still increasing.

"A few years a go [the radioactive water was increasing by] 400 tonnes per day, but the increase per day has now gone down to around 100 tonnes per day," said Naohiro Masuda, TEPCO's chief decommissioning officer.

"A few years ago we had to create one new tank every two or three days but now we need to increase one new tank every seven to 10 days, so in that sense we think it is progress, to a certain degree, in the sense it is a more stabilised situation," he said.

There are more than 1,000 tanks of contaminated water now at the site — and Government authorities have still not decided what to do with the water.

Experts want a gradual release, but if the tanks break the water would slosh out. ( AP: Daisuke Suzuki )

Ice wall of limited effect

TEPCO revealed earlier this week that its underground frozen soil wall — what was expected to be the main defence against groundwater contamination — had only had a limited effect.

The 1.5-kilometre-long barrier is designed to keep groundwater from flowing into reactor buildings that were damaged by the disaster.

The wall cost more than $US300 million to build and costs $US10 million to operate.

Mr Masuda said it was important to note that the combination of the company's measures to prevent contamination meant that the situation was less volatile overall.

So while the level of contaminated water is still increasing — albeit at a slower rate — the Japanese Government is yet to agree on what to do with it.

One controversial option includes decontaminating the water as much as possible and then gradually release it into the ocean.

Experts advising the Government have urged a gradual release of the water to the nearby Pacific Ocean.

Treatment can remove all the radioactive elements except tritium, which they say is safe in small amounts.

But local fishermen have balked at the idea, fearing a devastating impact to the reputation of their produce.

Satoru Toyomoto from the Japanese Ministry of Economy, Trade and Industry said a Government sub-committee was still considering its options.

"You may think after as many as seven years [this should be decided], but we have done our utmost and we have done all possible things and we have finally come to a stage where we can consider this," he said.

"After the accident occurred [in 2011] it was like a field hospital on a battlefield — but finally we have reached a situation where we can calmly think about the long-term future.

"A taskforce two years ago considered various options including geological disposal, vaporisation, burial underground, hydrogen release or release into the sea.

"Of those five options, we are trying to make a comprehensive assessment looking at options, but also reputational measures."