WASHINGTON - The US government plans to undertake the costliest modernisation of its nuclear arsenal in history, even though the military as a whole is facing stiff spending cuts, The Washington Post reported late Saturday.  The newspaper said there is no official price estimate for the effort to upgrade and maintain the 5,113 warheads in the inventory, replace old delivery systems and renovate the aging nuclear facilities.  But a study this summer by the Stimson Center, a Washington think-tank, estimated costs would be at least $352 billion over the coming decade, the report said.  Others say the figure could be far higher, particularly if the work is delayed even longer, the paper noted.

Upgrading just one of the seven types of weapons in the stockpile, the B61 bomb, is likely to cost $10 billion over five years, The Post noted.
It would cost up to $110 billion to build 12 replacements for the aging Ohio-class submarines, the paper added, citing estimates by the Congressional Budget Office.
According to the report, the Minuteman III ballistic missiles are undergoing a $7 billion upgrade.
At the same time, a nuclear-capable fleet of F-35 strike aircraft is being built to replace existing aircraft at a cost of $162 million an airplane, the paper pointed out.
Modernising the buildings and laboratories where the refurbishments will take place is expected to cost at least $88 billion over 10 years, the report said.