AECL released this information at a media briefing today as part of its commitment to public disclosure of activities related to the repair of the NRU at Chalk River, Ontario.
"Returning the NRU to service to support the production of medical isotopes for Canadian patients and healthcare practitioners is our primary objective", said AECL's President and CEO Hugh MacDiarmid. "We have a dedicated team working around the clock to bring the NRU back to operation as quickly and as safely as possible. However, it is a complex task with many variables", he said.
The duration of the shutdown continues to be founded on the best evidence available, including the most up-to-date analysis of the heavy water leak site, vessel condition, repair strategies, and critical path requirements for restart after an extended shutdown.
"We have identified three phases of our return to service plan.
Today we are progressing toward the end of phase one which involves a comprehensive condition assessment of the reactor, the development and testing of several repair options, and overall planning and critical path development", said MacDiarmid. "This work will contribute to a decision on the preferred repair strategy to pursue in phase two."
A decision on the repair method is expected in the next few weeks. Phase two of the return to service plan, effecting the actual repair, is estimated to take in the order of two months depending on the method determined, regulatory considerations, and further analysis of the extent of the repair required. Phase three, restarting and testing the reactor, is estimated to take an additional two months, based on AECL's previous experience of refilling, refuelling and start-up of the reactor in 1992.
To date, the leak site at the base of the reactor, which is approximately nine meters from the closest access location, has been thoroughly analyzed. More than 60 per cent of the reactor vessel's circumference has been surveyed using remote, non-destructive methods. The examination has revealed thinning of the wall at the leak site, and identified a total of nine areas of interest.
AECL metallurgical and material experts are working with external engineering firms having remote repair capability to determine the best methods for cleaning and repairing the reactor vessel.
Mock-ups of the affected area of the NRU vessel have been constructed to provide necessary on-site testing and training for vessel inspection and repair work, and a full-height mock up of a section of the reactor is currently being built.
"Chalk River staff have great technical expertise in the areas of remote inspection, material science, corrosion, and critical path development," said Bill Pilkington, AECL's Senior Vice-President and Chief Nuclear Officer. "All of the evidence to date supports the view that the NRU can be successfully returned to service. We have the experience and know-how to bring the NRU back into service safely and in the shortest time possible."
Further guidance on a return to service date will be provided as more data is collected and analyzed, and the decision is made about the repair technique and extent of required repairs.