Some of Washington's Western allies are seeking to end a US-driven de facto ban on transfers of nuclear fuel technology to countries wishing to enrich uranium for electricity production, diplomats say.
The moratorium has coincided with US-led efforts to stop Iran's enrichment drive and a new, six-country bid to control nuclear fuel supply that Washington says will deter secret atom bomb pursuits but which many nations see as discriminatory.
A July 15-17 summit of the Group of Eight (G8) industrial nations is expected to approve a year's extension of the moratorium on providing uranium enrichment and plutonium reprocessing technology to states not now making nuclear fuel.
But diplomats said the 2006 G8 summit would be the last time the world's top economies, which decide by consensus, would back the freeze on admitting new members to the enrichment club.
"We're laying down a marker that this is the last year this language will be in there," a senior Western diplomat said. Among those interested in opening the door to exporting enrichment activity for peaceful energy needs are Canada and Australia, with the world's largest and second-largest reserves of uranium respectively.
The reason for the curb on enrichment technology, which can be used to produce fuel for nuclear energy or nuclear weapons, has been the long dispute over Iran's enrichment programme.
Tehran hid this work from UN inspectors for 18 years until a group of Iranian exiles exposed it in August 2002, alleging the Islamic republic was secretly pursuing atomic weapons. Iran says it only wants to produce fuel for electricity.
The G8 moratorium was meant to give the Nuclear Suppliers Group (NSG), the 45 key producers of nuclear technology, time to come up with new export norms to prevent countries like Iran getting proliferation-prone technology. But the NSG has yet to specify key criteria, largely because Washington has not yet defined its position, diplomats said.