Cost of cleaning up UK Sellafield nuclear site still uncertain

* Cost of cleaning up Sellafield reached 53 bln stg last month

* Sellafield complex nuclear site, technical uncertainties

By Nina Chestney

LONDON, March 11 (Reuters) - The escalating final cost of cleaning up hazardous waste at Britain's nuclear site at Sellafield is still uncertain, as government officials and the site's owners and managers cannot not guarantee when costs would plateau.

Last year, Britain's Committee of Public Accounts criticised the management of Sellafield in northern England for huge cost overuns, delays on projects and expensive staff.

The cost estimate of cleaning up hazardous waste at Sellafield reached 53 billion pounds ($79.18 billion) in February, up 5 billion from March last year, and is expected to rise above 70 billion pounds.

The committee, which scrutinises whether taxpayers' money is spent wisely, on Wednesday asked the government, the site's owner the Nuclear Decommissioning Authority (NDA), Sellafield Ltd and former managers Nuclear Management Partners (NMP) whether costs would continue to rise.

"It is impossible to know that (...) we find difficulties at the site which are pretty much unprecedented," Stephen Lovegrove, permanent secretary at the government's Department of Energy and Climate Change, told the committee.

"I would hope (the cost estimate) won't go up and hope we are getting nearer to a place where the NDA and Sellafield Ltd are getting to grips with problems at the site."

"Do I have great confidence in that? The answer is probably 'no'," he added.

The business plan for Sellafield is expected to last for 120 years, reflecting the complexity and technical uncertainty of the site.

NMP, which consists of France's Areva, U.S. firm Aecom (NYSE: ACM - news) and Britain's Amec, has managed Sellafield since 2008 but Britain's NDA, which owns Sellafield, stripped it of the multi-billion pound contract in January, after concerns about performance at the site.

"For the rest of our estate, the (cost estimate) figure has stabilised. At Sellafield, I genuinely don't know," said John Clarke (Toronto: CKI.TO - news) , chief executive of NDA, adding that focusing on costs was misleading as it did not reflect improvements in performance at the site.

"We hope the provision will not go up. What we will see over the next four years is we will make more and more progress, learning more about the characteristics of what we are dealing with," added Tony Price, chair of the Sellafield Board. ($1 = 0.6694 pounds) (Editing by David Evans)