News and Information
Current status of OPAL research reactor (updated 25 August 2008)
The OPAL nuclear research reactor returned to full operational power on 23 May 2008 after a 10 month shutdown following approval by the nuclear regulator, ARPANSA to use a modified fuel design.
Since returning to operation the commissioning of neutron beam instruments and production of commercial quantities of several nuclear medicines has been progressively resuming.
Radiopharmaceuticals
An application has been lodged with ARPANSA for the irradiation of targets in OPAL, from which the radiopharmaceutical, technetium-99 is extracted. If approval is granted from ARPANSA to irradiate the targets then a testing program will commence, which includes target irradiation and subsequent processing. These tests are necessary to satisfy Therapeutic Goods Administration (TGA) requirements. After successful testing formal TGA approval will be sought to commence routine production of this important radiopharmaceutical. It is hoped that full commercial supply will commence by the end of the year.
Neutron-beam instrument status
So far five of the seven new neutron instruments have received their first neutrons, confirming that the instrumentswork properly. This is an exciting step towards commissioning completion. Four instruments called Echidna, Wombat, Koala and Kowari, designed to study the structure of materials, have now been granted operating licences by the regulator so can commence running scientific experiments. Two more instruments – Platypus and Quokka – are currently waiting for licence approval. During the shutdown these commissioning processes had to be placed on hold.
Silicon irradiation
Irradiation testing in silicon facilities has re-commenced with the reactor returning to service. Further testing will be conducted over the coming weeks. Irradiated silicon is used in the semi-conductor industry.
Operational matters
During the two week return to service program in May a number of reactor commissioning tests were repeated and it was demonstrated that the reactor was fully operational. Testing of various reactor capabilities continued through the operating cycle.
The reactor is shutdown for routine maintenance and refuelling approximately every month. In early July a routine shutdown was used to undertake further testing to fully assess a previously identified issue where reactor pool water (normal demineralised water) was mixing with the heavy water contained in the reflector vessel. The heavy water in the reflector vessel is used to reflect neutrons back to the core in order to sustain the nuclear reaction. Irradiation facilities are located within the reflector vessel to take advantage of the neutrons that are coming from and reflected to the reactor core.
During recent operation monitoring of the purity of heavy water indicated that the mixing of normal water with heavy water was continuing. The mixing, whilst not a safety issue, was first identified in 2006. A method for reducing the mixing was undertaken during the extended shutdown, which involved injecting microscopic alumina particles into the affected area. This solution was only partially successful and ANSTO is now examining several remedies with the reactor designer INVAP. ANSTO engineers have worked hard on these remedies and are confident that viable solutions can be implemented to reduce or eliminate the effects of the unwanted mixing of normal and heavy water.
In early August the reactor was shut down to investigate the functioning of one of the 5 control rods.
OPAL has now returned to power.
It is ANSTO’s intention to operate for two cycles and then replace the heavy water. After that shutdown the completion of the performance demonstration tests has been scheduled. Those tests are required under the contract with the reactor designers INVAP.
Background on extended OPAL shutdown
After nearly a year of successful operation, the OPAL reactor was shut down in July 2007 following a partial displacement of some fuel plates.
The problem lay with the imported fuel and was not related to the reactor design or functions.
The reactor core comprises 16 fuel assemblies in a four by four square matrix. Each assembly has 21 aluminium-clad fuel plates, each of which contains within it a quantity of low enriched uranium. Each standard plate is about 1.5mm thick, 80mm wide and 700mm high.
Investigations into the cause of the displacements indicated that a combination of factors was involved, involving both fuel design and manufacturing processes. This necessitated a change to the fuel design to avoid future plate movements.
There were no abnormal safety or radiation issues.
ANSTO continued to keep the community and customers regularly updated on progress during the shutdown. Nuclear medicine provision was maintained as far as possible through importation at additional cost to ANSTO.
ANSTO has been conscious of the unreliability of importation supply of radiopharmaceuticals which has highlighted the benefits of domestic production in Australia. Airline shipment interruptions typically occur every two to three weeks which can cause great inconvenience to patients, their families and nuclear medicine clinicians.