The OPAL research reactor will be shut down for two weeks from tomorrow for a regular monthly fuel change and to replace heavy water in its reflector vessel. This is a major step towards recommencing full nuclear medicine production and irradiation of silicon for the semiconductor industry.
Following return to full operation on or around 3 November, the first stage in re-starting production of the most used product, Technetium-99 can begin.
Technitium-99 is currently being imported which is costly and subject to periodic interruptions of supply.
The heavy water, which is located in the reflector vessel, is being 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 this is not a safety issue and does not prevent operation of the reactor, the dilution reduces neutron intensity, which in turn can affect the ability to irradiate targets for radiopharmaceutical production and silicon irradiation.
Changing the heavy water will allow a full demonstration of OPAL’s capabilities. Production of molybdenum-99 (the precursor to technetium-99m) requires a series of tests, commissioning phases and regulatory approvals before product can be supplied to patients. It is anticipated this will be complete early next year.
During the current operating reactor cycle the reactor successfully provided neutrons for research and commercial irradiations including several radioisotopes used in nuclear medicine.
Another major achievement in the past two months is that six of the seven new neutron beam instruments attached to OPAL are now on line with four of these having received operating licences. 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: 17/10/2008