Former Australian Prime Minister John Howard inspects the OPAL reactor at official opening in April 2007. Source: Cosmos

The nuclear research reactor OPAL in Australia is working again after a 10-month break in the production of radioisotopes due to faulty uranium alloy fuel plates in the reactor's core.

Though the shutdown has cost millions of dollars and delayed medical and science research, there is a buzz around the facility with the restart of OPAL and a great sense of relief and excitement among scientists, said Ron Cameron, chief of operations at the Lucas Heights site near Sydney, according to Cosmos.

The nation's only reactor, which had experienced a self-sustaining series of nuclear fission reactions, received approval on May 9, from the regulatory body, the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA), to restart production.

Low-power testing of the full reactor core of 16 fuel rods commenced last week. This is part of the process towards reaching full power, which the Australian Nuclear Science and Technology Organization (ANSTO) said it expects will take several weeks.

OPAL (Open Pool Australian Lightwater reactor) has a 20-megawatt capacity and last year replaced the long-running research reactor, HIFAR (High Flux Australian Reactor).

This is the first time the reactor has been up and running since it was closed in July 2007, several months after the official opening. OPAL operated for a year before technicians noticed that several of the fuel plates had come loose within the fuel assembly, according to Cosmos.

The aluminium-uranium plates, which are cold-welded into place in slots in the assembly, shifted out of their slots because of vibrations in the heavy water surrounding the core, reported ANSTO.

According to Cameron, the vibrations would have eventually shifted the plates out of their slots and into the surrounding heavy water, but said this was an operations issue rather than a safety issue.

The fuel assembly has now been redesigned with a double stopper across the top of the box-shaped apparatus, so that plate movements would be confined to just a few millimeters if the welds were to break again, he added.

The organization has also switched fuel manufacturers from Argentine company CNEA to a French manufacturer, CERCA, which Cameron said was the only company capable of recreating the elements needed to restart the reactor in time and to the new design specifications. Both the fuel and the new design were reviewed by regulating body ARPANSA prior to the reactor's restart, reported Cosmos.