The operator of Japan's tsunami-crippled nuclear plant is to cover a large swathe of seabed near the battered reactors with cement in a bid to halt the spread of radiation, the company said Wednesday.

A clay-cement compound will be laid over 73,000 square metres (785,000 square feet) of the floor of the Pacific in front of the Fukushima Daiichi plant on the nation's northeast coast, said Tokyo Electric Power Co. (TEPCO).

The area is equivalent to around 10 football pitches.

"This is meant to prevent further contamination of the ocean... as sample tests have shown a relatively high concentration of radioactive substances in the sea soil in the bay," a company spokeswoman said.

Reactors at the plant went into meltdown after their cooling systems were knocked out by the monster tsunami of March last year, which was generated by a huge undersea earthquake.

Contaminated water from the plant leaked into the sea and radioactive particles concentrated on the seabed. Scientists fear ocean currents could pollute areas further afield.

The cover will be 60 centimetres (24 inches) thick, with 10 centimetres expected to be eaten away by seawater every 50 years, the TEPCO official said.

Intense US questions early on over Fukushima
Washington (AFP) Feb 22, 2012 - US officials voiced concern about a lack of information after Japan's Fukushima nuclear disaster and issued a controversial warning not to go near the plant after intense discussions, transcripts showed.

Transcripts of the Nuclear Regulatory Commission, released ahead of the one-year anniversary of the crisis, showed that US officials at times relied on information from the media as Japan initially declined assistance.

"We're getting various information from various sources, most of which is either conflicting or supporting the little bit of information that we actually have," Martin Virgilio, a senior official in charge of nuclear safety, said in one transcript shortly after the March 11 tsunami smashed into Fukushima.

Nuclear officials debated at length over a decision to urge Americans to stay out of the 50-mile (80-kilometer) radius around the Fukushima Daiichi plant, a wider no-go zone than that put in place by Japanese authorities.

"If this happened in the US, we would go out to 50 miles. That would be our evacuation recommendation," Bill Borchardt, the commission's executive director for operations, said in the transcripts.

The transcripts showed that the commission considered a larger evacuation if the situation deteriorated or the wind changed direction. Several European countries issued dire warnings and urged residents to leave Tokyo.

The no-go zone advice came as Nuclear Regulatory Commission's chairman, Gregory Jaczko, told a congressional committee on March 16 that Reactor No. Four's pool for spent fuel had dried, meaning its ability to keep cool was severely diminished and radiation would spike.

That assessment turned out to be inaccurate. The transcripts showed Jaczko had discussed the spent fuel pool with aides, knowing that he would be asked the question during his appearance on Capitol Hill.

"I'm going to say (the assessment) is from a team that is in Japan that is embedded that is working closely with the Japanese utility and the Japanese regulatory agency, is that correct?" Jaczko asked.

Senior officials replied in the affirmative, although one staff member -- apparently speaking when Jaczko was no longer on the conference call -- disputed the assessment.

Last year's earthquake set off a tsunami that left more than 19,000 people dead in Japan's worst post-World War II disaster. While the disaster crippled the Fukushima plant, the nuclear crisis has not directly claimed lives.