OFFICIALS at the nuclear reactor in Lucas Heights have rejected recent media reports that technical delays in the new $400 million OPAL reactor threatens the supply of isotopes used in medical diagnostics and treatment.

Instead, they have pointed out the reactor's near-faultless operation, which should make Australia self-sufficient in medical isotope production within weeks.

Andrew Humpherson, general manager of public affairs at the Australian Nuclear Science and Technology Organisation (ANSTO), said the reactor had achieved world's best-practice levels, and had been operating at "over 99 per cent availability '' in recent months.

"This is well above world average,'' he said.

Production of molybdenum-99 stopped in January, 2007, with the permanent shutdown of the former reactor and the starting up of the new OPAL reactor.

Further delays occurred for 10 months in July, 2007, with a fuel design problem when 13 aluminium plates containing the uranium fuel worked loose inside some of the 16 fuel rods. Molybdenum isotopes are used in making key diagnostic radiopharmaceuticals, particularly those used for cancer and heart diagnosis and treatment.

This had meant ANSTO had to import $100,000 of isotopes each week from reactors in other countries, mainly South Africa.

But Mr Humpherson said not only had ANSTO fixed the technical glitch, with OPAL operating ``brilliantly for the past year'', but it would soon supply all commercial domestic isotope needs.

"We could potentially supply other countries,'' he said.

Mr Humpherson said the main problem was the limited number of nuclear plants producing isotopes worldwide, rather than anything specific to do with the Lucas Heights reactor.

A recent global shortage was triggered when a heavy water leak forced a Canadian reactor to close, while maintenance problems at plants in South Africa, France, Belgium or the Netherlands can create an international shortage. A Dutch reactor is scheduled to be shut down for maintenance in mid-July.

Mr Humpherson said the OPAL reactor was the newest of its type in the world. OPAL (open pool Australian lightwater reactor) is a 20 megawatt reactor which uses low-enriched uranium fuel, and is cooled by water.