The OPAL research reactor is at full operation following the successful replacement of its heavy water, which occurred during the last shutdown. The first stage in re-starting production of the most used nuclear medicine, technetium-99m will occur in mid-November when irradiation of special uranium plates begins.
Returning to power with new heavy water is not only a major step towards recommencing full nuclear medicine production, but allows irradiation of silicon for the semiconductor industry. It will also permit assessment of the full performance of OPAL.
The heavy water, located in the ‘reflector vessel’, was replaced because over the past two years, normal water from the surrounding reactor pool has slowly seeped in and diluted it. Heavy water reflects neutrons back into the reactor core to sustain the nuclear reaction.
Although not a safety issue and does not prevent operation of the reactor, dilution reduces neutron intensity, which can affect the ability to irradiate targets for radiopharmaceutical production and silicon irradiation.
The first stage of technetium-99m production begins when uranium plates are irradiated in the reactor. These plates are then taken to the radiopharmaceutical production plant, where molybdenum-99 is extracted. However, before the product can be delivered to hospitals for patient use, a series of tests are required. These will occur during the commissioning phases and provide the information needed for regulatory approvals. It is anticipated that full production will be underway early next year.
Technetium-99m is currently being imported which is more costly and subject to periodic interruptions of supply.
Despite the heavy water dilution, OPAL has already successfully provided neutrons for research and commercial irradiations, including several radioisotopes used in nuclear medicine.
Another major achievement over the past few months is that six of seven new neutron beam instruments attached to OPAL are now on-line with four of these licensed to run experiments.
This is great news for Australian scientists. The water seepage was first identified in 2006. During a 10 month shutdown in 2007-08, to fix an unrelated fuel design fault, ANSTO and Argentine designers INVAP started investigating ways to permanently fix the seepage points. This investigation is still ongoing.
All rectification of defects is the responsibility of the reactor designers INVAP and once repairs are complete and OPAL is operating to ANSTO’s satisfaction, negotiations will be finalised regarding costs.
Published: 07/11/2008