Progress report

Three fuel assemblies were found to have partially dislodged plates during the regular monthly fuel change. A further two assemblies have since been found to also have minor plate movement.  Each assembly has 21 fuel plates which are 'crimped' into an aluminium frame.

The cause is believed to be a manufacturing issue; however all possibilities are still being assessed.

The reactor and its 16-fuel assembly core had functioned very well since full power was reached in November 2006.

Fuel assembly

The Iimplementation of a solution to the problem of dislodged plates in fuel assemblies of the OPAL research reactor, initially estimated initially to take eight weeks, is expected to take longer to complete.

Analysis and testing of the fuel assembly fault has been undertaken by the fuel manufacturer in Argentina and is nearing finalisation.

Once completed, these tests will enable a clear path forward to be established. Returning to operation will then require approval by the independent safety regulator ARPANSA.

Detailed examination and removal of the fuel assemblies, including taking high resolution video footage of the fuel elements at the bottom of the 13 metre deep reactor pool, has been painstaking and has required progressive approval and consultation with ARPANSA.

Good progress is being made and a clear solution is expected to be put to the regulator, ARPANSA,soon.

Because safety is paramount, resolving the problem takes time since activities must be subjected to thorough assessment and often independent regulatory approval.

The responsibility for fixing the problem is with the reactor designer under the reactor warranty. A clear time frame for return to operation will be given as soon as possible.

There are no safety or radiation issues. The shutdown is affecting silicon irradiation customers as well as causing delays and inconvenience to scientists involved in neutron beam research.

Radiopharmaceutical customers are less affected but are being kept informed. Supplies of the major reactor-produced nuclear medicines will continue to be provided through import and distributed by ANSTO, so patient treatments will be maintained.

The shutdown has enabled the process to resolve an internal leak, which was causing minor heavy water dilution, to commence. This problem was identified earlier this year and, whilst not affecting the reactor's steady performance to date, needs to be remedied to avoid the reactor's efficiency diminishing over an extended period of time.

What are fuel assemblies?

Fuel assemblies forming the reactor core

Fuel assemblies each hold 21 aluminium-laminated plates of uranium. The reactor core contains 16 of these assembles which are 8cm square and just under a metre long. The 16 assembles sit in a square array of four by four. The reactor core sits in the middle of the reflector vessel which is designed to 'reflect' neutrons produced back into the core to maintain the nuclear reaction.

Who makes the fuel?

The fuel currently in the reactor was manufactured in Argentina by CNEA . There are other producers in France and the USA that can also supply ANSTO with fuel. The manufacturer prepares the fuel plates which they then assemble into an assembly.

Seepage

Since OPAL commenced operation there has been one other significant equipment-related issue that also needs rectification. This is the heavy water dilution issue reported earlier this year, where a small amount of light water from the reactor pool is seeping into the heavy water contained in the reflector vessel.

Whilst this does not affect safety or operation, if left unresolved it will ultimately affect the performance of the reactor.

Discussions have been taking place with INVAP, the reactor's designers and builders about how to fix the problem. It is anticipated that during this shutdown period they will take the necessary action.

How will the water dilution problem be rectified?

To solve the dilution problem, further pressure testing is required followed by approval of the INVAP recommended remedy by ANSTO, and by ARPANSA - the independent nuclear industry regulator.

Are there any safety issues for ANSTO staff or the public?

No. The problems are purely operational and, although inconvenient, there are no current safety or radiation issues involved.

Who is responsible for safety?

ANSTO has strict safety regulations and all operational staff have initial responsibility, which is overseen by ANSTO' s Safety and Radiation Services. The independent regulator ARPANSA also routinely checks that safety standards are being applied.