Workers racing against time are building a wall of steel and enclosing materials in the sea on Saturday, just outside the crippled Fukushima nuclear power plant to prevent radioactive water seeping into the Pacific Ocean.

The engineers plan to build 120 metre wide wall of steel sheets to form a 'silt curtain' for the radioactive material, as the reactor makers Toshiba submitted drafts to the government to decommission the four stricken units in around 10 years time, Kyodo news agency reported, quoting Japanese officials.

After struggling for weeks to contain radioactivity at the crippled plant, the engineers apparently have decided to go for decommissioning of the affected units. Kyodo said, the time frame submitted by the reactor makers was around two thirds of the time taken to dismantle the three Mile Island nuclear plant in the US after a 1979 incident in which part of a reactor core melted.

With the world's worst nuclear accident since Chernobyl dragging on for months with no end in sight, the government woes were compounded with residents of towns, surrounding the crippled nuclear plants starting to return homes, in defiance of warnings to stay away.

The workers also stepped up efforts to remove highly radioactive water from a tunnel of reactor Nos 2, as they try to cool their cores and plug leaks amid warnings that the crisis is far from over. Tokyo Electric Power Company says contaminated water in a concrete tunnel of the number 2 reactor has risen 10 centimeters since leakage of the water into the ocean stopped on Wednesday, the NHK News reported.

Meanwhile, economy, trade and industry minister Banri Kaieda, meanwhile, met with Fukushima gov. Yuhei Sato in the city of Fukushima, and plans to visit the crippled Nuclear Power Station later in the day. The visit, aimed at encouraging those engaged in stabilisation efforts and checking on the plant's damaged reactors, would be the first by a Cabinet minister after the six-reactor plant was rocked by explosions and began spewing radioactive materials in mid-March.

The power supplier stopped the leakage of water contaminated with radioactive materials from near the intake on Wednesday. But facing mounting environmental concerns, it hopes that the installation will help prevent contaminated water from spreading outside the plant's bay. The radioactive iodine reading was 63,000 times the legal limit in seawater near the intake a day after contaminated water stopped leaking into the sea.

Along with the efforts to stop the leakage, the utility also released about 9,000 tons of water containing relatively low-level radioactive materials into the sea to free up room to pool contaminated water that has flooded the No. 2 reactor's turbine building and a tunnel outside it. The company, known as Tepco, also continued to pump nitrogen, an inert gas, into the No. 1 reactor to prevent hydrogen from exploding, while enhancing the purity of the gas to reduce the amount of oxygen mixed in it, the Kyodo news reported.

Tepco said it will fly a small unmanned helicopter to survey the plant, possibly starting on Sunday, depending on the weather. The drone is expected to capture images of damaged installations at the Nos. 1 to 4 reactors that workers would find it hard to approach due to elevated levels of radiation.

During a meeting with governor Sato, industry minister Kaieda inquired about what local residents' requests are as the government has directed those living within a 20-kilometer radius of the plant to evacuate to ensure their safety. Speaking to reporters after the meeting, Kaieda, whose ministry promotes and regulates the nuclear industry, said the situation was far from being brought under control and expressed his resolve to contain it as soon as possible.

On the nation's atomic energy policy, he said: "While I can't say at this point, we need to review standards to enhance safety."

Also Saturday, the government's nuclear safety agency called on the nation's power suppliers to have at least two backup diesel generators on standby even when a reactor is in a stable condition called ‘'cold shutdown’ or undergoing fuel replacement. The move came after all three diesel generators failed to function at the Higashidori nuclear power plant in Aomori Prefecture at one point following the 7.1-magnitude aftershock the March 11 deadly earthquake.

The agency's previous rule that required the suppliers to have just one diesel generator on standby in situations including cold shutdown was ‘not enough, I must say,’ Hidehiko Nishiyama, a spokesman for the Nuclear and Industry Safety Agency, said at a news conference.

Nishiyama also displayed candor about the missteps and failures that precipitated the disaster, saying: "We had said all along that (nuclear power) was absolutely secure thanks to its multiple layers of protection and five-layer barriers, and I believed this, but we brought this situation onto ourselves." "We need to review everything to ensure safety, regardless of precedents," he said.