Another shortage of medical isotopes in Canada looks imminent as the unscheduled shutdown of the NRU reactor facility is now expected to last at least three months.
|The building housing the NRU reactor (Image: AECL)
The reactor, which provides a large share of the world's medical isotopes, has been shut down since the discovery of a minor leak in mid May. However, investigations into that issue have uncovered more necessary repairs.
Bill Pilkington, senior vice-president and chief nuclear officer of the reactor's owner and operator AECL, has now said, "Sophisticated diagnostic procedures are required to determine the exact nature and extent of the repairs before returning the NRU reactor safely to service." He added, "Based on our preliminary findings to date, we now believe that the NRU reactor will be out of service for at least three months."
Hugh MacDiarmid, president and CEO of AECL, commented: "Until all investigations are completed, it is premature at this point to set a definitive timeline for the return to service of the NRU reactor."
A regional loss of electrical power on 14 May caused the reactor at the Chalk River facility to shut down. However, during routine monitoring prior to a restart, a small leak of heavy water was discovered. According to AECL, the water was leaking at a rate of 5 kg per hour. The company has now lowered the heavy water level in the reactor vessel, which has reduced this leak rate by approximately 25%. The heavy water is fully contained and is being stored in specially designed drums. A small release of tritium also occurred as a result of evaporation, which was at a level below what would be a threat to the public or to workers but still requiring AECL to notify regulators the Canadian Nuclear Safety Commission (CNSC).
The source of the leak is at the base of the reactor vessel, in a location where there is corrosion on its outside wall. AECL said that an initial inspection of the external wall at the base of the reactor vessel using remote cameras has indicated additional corrosion points that will require further examination. Test equipment is being prepared for an inspection of the internal of the reactor vessel.
AECL initially anticipated that the reactor would be out of service for over a month and that it would not be able to meet production requirements for medical isotopes from 23 May onwards. That now looks more likely to be the end of August.
Many radioisotopes used for medical purposes are extremely short-lived so an unexpected interruption to production can quickly affect supplies. An extended outage of the NRU at the end of 2007 prompted an isotope supply emergency when the reactor was shut down because required repairs had not been carried out. Within days isotope supplies began to run out and many thousands of medical procedures were cancelled.
World isotope supplies were rocked later in 2008 when key reactors in Belgium, Canada, France, South Africa and the Netherlands, which between them provide about 85% of the world's cobalt-60 supply and virtually all of the technetium-99m and molybdenum-99, were undergoing refuelling and maintenance within weeks of each other. Currently, the High-Flux Reactor at Petten in the Netherlands is operating on a temporary license until it too can be repaired. The elderly nature of the reactors that are so vital to nuclear medicine supplies is a worldwide cause of concern.
Researchers in several countries are working on ways to produce medical isotopes by novel routes that do not rely on nuclear reactors, but the techniques are not yet commercially viable.