The United States spent at least $US52 billion ($77 billion) on nuclear-related programs last year, most of it to maintain and refurbish its arsenal of nuclear weapons, a report has said.

The report by the Carnegie Endowment for International Peace said the estimate was pieced together from publicly available documents because the Government does not track overall spending on nuclear-related programs.

"Total appropriations for nuclear weapons and weapons-related programs in fiscal year 2008 were at least $US52.4 billion, according to the best available data," the report said.

It said the Defence Department's costs of deploying and maintaining nuclear weapons was a partial estimate, and therefore the figure may be too low.

Even so, the report said, it was far larger than most officials would acknowledge.

"About 55.5 per cent [$US29.1 billion] of all nuclear expenses go toward upgrading, operating, and sustaining the US nuclear arsenal," the report said.

"These costs will increase significantly if the Doe's [Department of Energy's] proposals to rebuild the nuclear weapons production complex and resume the production of nuclear weapons are approved and funded," it said.

The cost of sustaining the US nuclear arsenal by itself was an estimated $US5 billion dollars, the report said.

By comparison, $US5.2 billion (9.9 per cent of the total) was devoted to preventing the spread and use of nuclear weapons and nuclear technology in fiscal 2008, it said.

Threat reduction programs do not require the same level of spending as maintaining nuclear forces, the report acknowledged.

But it said the disparity in the spending priorities "sends a message to the rest of the world that the United States considers preserving and enhancing its nuclear options more important than preventing nuclear proliferation."

-AFP