Jan. 30 (Bloomberg) -- The U.K. Nuclear Decommissioning Authority, created in 2005 to clean up atomic sites, should do more to quantify costs after budget estimates rose 18 percent, the National Audit Office said.

``The authority should determine the reasons for the continuing increases in cost estimates submitted by the sites, in particular on those elements of work which, by now, should have been reliably costed,'' the government's spending watchdog said in a report published today.

Britain is tackling the decommissioning of its oldest nuclear sites as utilities plan new reactors to help prevent a shortfall when a third of the country's power plants are shut down. Business Secretary John Hutton said Jan. 10 the government will help clear the way for developers to build at least one nuclear plant before 2020. The U.K. doesn't yet have a final storage site for radioactive waste.

Mark Leggett, the director of the commercial division of the decommissioning authority, resigned and will leave the company tomorrow, spokesman Bill Hamilton said today by telephone. He'll be replaced on a temporary basis by Sean Balmer, who was previously the head of commercial revenue, Hamilton said.

Leggett decided to step down ``for personal reasons,'' Hamilton said. ``It's not true it has anything to do with the NAO report. He was well thought of here,'' he said.

Costs Escalate

The nuclear authority, funded by taxpayers and income from nuclear operations, said last year that decommissioning its 19 sites over a 100-year period may cost 73 billion pounds ($145 billion), up from an estimate of about 61 billion in 2005. The body is the first to attempt to determine the cost of cleaning up the U.K.'s radioactive sites, such as the Dounreay atomic research station in Scotland.

The NAO suggested the authority should detail the reasons for cost increases and provide a range of estimated expenditures for areas that remain uncertain. It should also develop a strategy to fix some prices with contractors working on its sites, the audit office said.

In addition, costs have risen because volatile earnings from ``ageing and unreliable commercial facilities'' have caused it to start and stop work at some sites, the audit office said.

``One of our primary roles going forward is to provide a level of certainty for our stakeholders,'' the authority said in a statement on its Web site today. ``This will require a combination of stable funding, high-quality plans and delivery against cost and schedule by our contractors.''

Nuclear Liability

The authority expected costs to climb in the ``early years'' as it assessed the task of cleaning up the sites, it said. ``We remain confident that through innovation and world-class performance by our contractors we will first stabilize and then ultimately reduce the U.K.'s nuclear liability,'' it said.

The decommissioning body manages waste from civil nuclear programs that were state sponsored before the power industry was privatized. Its remit includes former electricity plants and fuel-processing sites at Sellafield, on the northwest coast of England.

To contact the reporter on this story: Paul Dobson in London at pdobson2@bloomberg.net

Last Updated: January 30, 2008 06:20 EST