THE company planning the largest nuclear project in the United States - two giant reactors in South Texas - is giving up and writing off its investment of $US331 million ($A315 million) after uncertainties created by the accident in Japan.

But the project - planned by NRG, a New Jersey-based independent power producer, and its minority partner, Toshiba - was in considerable doubt even before the accident at Fukushima began on March 11. Texas has a surplus of electricity and low prices for natural gas, which sets the price of electricity on the market there.

The project could go forward if circumstances changed, said David Crane, the chief executive of NRG, but he said the prospect of that occurring was ''extremely daunting and at this point not particularly likely''.

The plan for two reactors in South Texas was identified more than two years ago by the US Energy Department as one of the four candidates for loan guarantees that were authorised by the 2005 Energy Act.

It is the second of the four projects to die; Calvert Cliffs 3, in Maryland, seems unlikely at this point because Constellation Energy could not reach financial terms with the Energy Department. The department has granted a conditional loan guarantee to one project in Georgia and may give another to a project in South Carolina.

In a conference call with investment analysts this week, Mr Crane said that in order to proceed with the project, the federal government would probably have to institute a ''clean energy standard'' that would create quotas for nuclear power, as states have already done for wind and solar.

He said Toshiba, which is writing off $150 million for the project, would continue to pay to proceed with a licence application with the Nuclear Regulatory Commission for the time being, on the chance that a new investor would be found. But, he said, ''We have concluded that financially, this is the end of the line for us.'' If the plant goes forward, he said, ''it will have to be funded by somebody else's resources''.

Tom Smith, an organiser in Austin with consumer advocates Public Citizen and a long-time campaigner against the project, cited higher construction costs and uncertainty after the accident at the Fukushima No. 1 nuclear power plant in Japan.

''The wheels are starting to fall off the nuclear renaissance,'' he said.

NEW YORK TIMES