Critically flawed: Former Australian Prime Minister John Howard inspects the OPAL reactor during the official opening of the site in April 2007.
Credit: ANSTO
SYDNEY: The Australian nuclear research reactor OPAL is working again after a 10-month hiatus due to faults with 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.
The nation's only reactor reached criticality – a self-sustaining series of nuclear fission reactions – on May 9, after approval to start up was granted by the regulatory body the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA).
Shifty plates
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 Organisation (ANSTO) 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.
The aluminium-uranium plates, which are swaged (cold-welded) into place in slots in the assembly, shifted out of their slots because of vibrations in the heavy water surrounding the core. ANSTO describes the malfunction as a combination of inadequate design and manufacturing faults with the Argentine fuel rods.
Cameron said the vibrations would have eventually shifted the plates out of their slots and into the surrounding heavy water, but that 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 millimetres if the welds were to break again.
Flow-on effects
The organisation 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.
