The worldwide shortage of medical isotopes is likely to be exacerbated by the delayed restart of Canada's vital National Research Universal (NRU) research reactor. The reactor's operator now expects it to restart in early 2010.
|Workers inspect the NRU reactor (Image: AECL)
The NRU reactor at Atomic Energy of Canada Ltd's (AECL's) Chalk River laboratory has been out of action since a small leak of heavy water was found on 15 May. Investigating every part of the vessel that may have suffered corrosion has been a lengthy process, in part because it required the three-week-long process of removing fuel, but also because the inspection could only be carried out remotely through a 12 centimetre hole some nine metres above the inspection site.
AECL had previously expected the 50-year-old reactor to return to service in late 2009. However, it has now said that a detailed analysis of data of non-destructive examination of the reactor confirms that nine sites probably require repairing. It added that high resolution scanning data available recently has identified both wall thinning and localized pitting that suggests different corrosion effects.
The company is considering applying the weld build-up technique over a broader area or band at the inside base of the reactor vessel wall, which will address all nine of the sites that have been identified. AECL noted, "In view of the number and locations of the repair sites, the band weld build-up application may be a more efficient and durable way to proceed in repairing the reactor vessel."
AECL said that it continues to look at an alternative mechanical repair technique, in order to address conditions not conducive to band weld repair. Both techniques are being advanced simultaneously to provide assurance that the appropriate repair technique is available when needed.
In a statement, AECL said: "At this time, the application of the band weld build-up technique, and the increased number of sites, indicates the NRU will return to service during Q1 2010."
Work continues with specialized vendors on proving repair tooling designs and fabrication of the equipment. Qualification testing of the repair tools will be required following manufacture. Testing of the repair process and special tools will be carried out on the full height mock-up assembled in the former NRX reactor. The mock-up will be used to train employees on the specialized repair tools.
The NRU reactor produces about one-third of the world's supply of isotopes for nuclear medicine. Its unplanned, extended shut down has therefore led to a shortage of medical isotopes. Production reactors in Europe and South Africa have coordinated their refuelling and maintenance schedules to give maximum availability and medical centres worldwide have been able to cope.
However, the second most prolific producer of isotopes, the HFR at Petten in the Netherlands is also in need of repair. It also has a minor leak, with tiny bubbles of gas passing from a pipe wall into the primary cooling system, but this pipe will be difficult to repair as it is located underneath the reactor and encased in concrete which also forms part of the biological shield. The reactor's operator, NRG, has an extraordinary licence to run the reactor in its current interim state until March 2010, but then must make the major repair.