Mr. Chairman, NRU shut down automatically on May 14 due to a loss of off-site power. A decision was made not to restart due to evidence of a heavy-water leak. The small heavy-water leak, which was the cause of the extended shutdown, continues at about four to five kilograms an hour.
I refer you to slide two in the material you were given, which shows the general layout of the NRU reactor and how we manage the heavy-water leakage. All of the heavy water from the leak is being collected and stored in specially designed drums. About 20% of the heavy water evaporates and results in a monitored airborne release from the Chalk River site. As a result of the leak, tritium emissions are just above the specified action level at which AECL reports to the CNSC and to our local stakeholders and posts to the AECL website. However, these emissions are at approximately one one-thousandth of the regulatory limit.
The leak location was identified four days after shutdown, using remote camera inspection due to the extreme difficulty in accessing the location from the top of the reactor, nine metres above.
I refer you to slide three, which shows the leak location, nine metres below the access points at the top of the reactor, and shows a detailed view of the configuration of the leak location. The leak was caused by corrosion starting on the outside wall of the vessel at the base. Specifically, nitric acid formed from radiation effects on the nitrogen in air and water at the base of the vessel. Full video inspection of the base of the reactor vessel indicates one other area similar to the leak location and half a dozen other areas of concern.
I refer you to slide four, which shows the leak location on the circumference of the vessel and the five additional black dots indicating the other areas of concern. Preliminary assessment of the extent of the corrosion and available nuclear repair technologies confirms there is no immediate or simple solution. This judgment is reflected in our recent guidance of at least a three-month outage.
Slide four has three photos: number one, when the vessel was new; number two, representing the general condition at the base of the vessel; and number three, showing an area of concern. Inspection and repair activities are complex due to limited access to the leak and corrosion location and by the surface condition on the vessel walls.
We are currently removing the fuel from the reactor. We will then drain the heavy water and do non-destructive examination on the inside wall at the base of the vessel. We will select the most appropriate cleaning and repair technique, and all work must be done remotely, due to access from the top of the reactor and high radiation fields. Only when we know the extent of repair and the technique can we produce a detailed plan and schedule for the work.
In parallel with the repair and inspection, we will complete an assessment to confirm that the vessel is fit for service. We are keeping the CNSC inspectors directly involved at the Chalk River site and officials in Ottawa fully informed of all our activities. Our repairs will be sound and our fitness for service assessments will be complete and accurate in order to facilitate a CNSC decision that it is safe for the NRU reactor to return to service.
AECL is fully committed to transparency with you, the CNSC, and our stakeholders. Returning the NRU to safe, reliable operation to support medical isotope production is our primary objective.
Thank you, Mr. Chair.
