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.

The shutdown has not only been expensive, but has also delayed important research.

Like its predecessor, OPAL irradiates materials to produce isotopes used in medical imaging. These have been imported through the period of OPAL's shutdown, costing ANSTO A$500,000 per month in lost radiopharmaceuticals orders. Income was also lost as OPAL was unable to carry out irradiation (or 'doping') of silicon to produce semiconductors, the sale of which was slated to bring ANSTO an estimated A$4-5 million a year.

Nuclear medicine specialist Kevin Allman, from the Nuclear Medicine Department at the Royal Prince Alfred Hospital in Sydney, said that although ANSTO maintained the regular supply of medical radioisotopes for medical diagnosis and therapy during the reactor shutdown, OPAL coming back online now offers the potential for expansion into new radionuclide products.

In addition to irradiating materials, OPAL possesses a suite of instruments used in medical and materials research to investigate how things behave at sub-atomic levels, including how proteins interact in the human body and how superconductors work.

The loss of time on the neutron beam instruments was a major disappointment to scientists, but Cameron doesn't think it will alter their expectations of the facility's performance. "In the period [OPAL was] operating, the instruments performed really well, so I don't think people are concerned," he said.

Disappointed by delays

While the delay was disappointing, it's not unusual for a large, complex engineering project, said University of Sydney biophysicist Jill Trewhella. The shutdown delayed her ability to do important research with students and meant she had to travel to the U.S. to make progress on biological neutron scattering studies.

"The logistics are difficult; transporting fragile biological samples across oceans and continents, making everything work perfectly in a short window of time that we are allocated," she said. "On the positive side, we have been successful and my students have had the unique experience of international 'big' science facilities."

Greg Warr, a physical chemist, also from the University of Sydney, said the delay had kept neutron scattering research in the same position they have been for the past 20 years – where researchers were expected to travel far and tended to be conservative with experiments because they had to pack everything on a plane.

He said that while the delay had negatively affected his research, he was delighted that the reactor was now up and running. Both Warr and Trewhella hoped to get beam time on OPAL's small angle neutron scattering instrument 'QUOKKA' within the year.

Rescheduling of the research timetable should have happened by the time the reactor reaches full power in June 2008, said Cameron. Local scientists who are able to travel quickly to the site will be first in line to use the instruments.