Repaired isotope reactor back in operation

18 August 2010

Canada's National Research Universal (NRU) reactor at Chalk River, which has been offline for repairs for the past 15 months following the discovery of a heavy water leak, has finally resumed the production of vital medical isotopes. 


NRU building (AECL)
Back in action - the NRU at Chalk River (Image: AECL)
Atomic Energy of Canada Ltd (AECL) reported on 17 August that low-power testing of the NRU reactor - one of the world's major radioisotope producing reactors - had concluded. "As a result, the reactor is now operating at high power and can begin to create medical isotopes," the company announced.


A heavy water leak from the reactor vessel at NRU was discovered in May 2009. To repair it, AECL had to defuel the reactor, drain its heavy water, carry out in-depth inspections, and then repair those parts of the reactor vessel where corrosion had caused structurally significant thinning of the vessel wall. This entailed the development of specialised tools to carry out the work, with operatives then being trained to use the equipment and qualification of the techniques being carried out on full-height mock ups of the NRU vessel constructed at the Chalk River site. AECL has also been required to develop a strategy to mitigate future corrosion problems.


The complexity of repairing the reactor led to several delays in bringing the NRU back into operation. However, in early July, Canada's nuclear regulator - the Canadian Nuclear Safety Commission (CNSC) - approved the return to service of the reactor. At that time, AECL expected to resume isotope production by the end of July.


However, the return of the reactor was delayed further due to problems with a specific set of reactor instrumentation which was not responding as expected during fuel loading. The instrumentation, which is important for safe operation of the reactor, was replaced.


The extended outage of NRU, which produces 40% of the world's molybdenum-99, has had a significant impact on the world's supply of radioisotopes. During its outage, suppliers of medical isotopes have been forced to find alternative sources and the number of medical procedures using isotopes has been cut back.


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.


AECL supplies NRU's output, plus the smaller quantities of radioisotopes produced in some of its power reactors, to Canada's MDS Nordion, which provides medical isotopes for molecular and diagnostic imaging, radiotherapeutics and sterilization.


Last week, MDS Nordion announced that it had extended its existing agreement with Ontario Power Generation (OPG) until 2020 for the supply of cobalt-60, used in gamma sterilization technologies.


Researched and written

by World Nuclear News