Chalk River Information Bulletin

(2009 August 12) The following information bulletin is in accordance with Atomic Energy of Canada Limited's (AECL) ongoing commitment to voluntary public disclosure of events related to the Chalk River Laboratories (CRL).

Detailed analysis of Non Destructive Examination (NDE) data collected to date confirms nine sites likely requiring repair. In addition, high resolution scanning data available recently has identified both wall thinning and localized pitting that suggests different corrosion effects. This data points to the need to better understand the nature of the corrosion mechanism. As a result, AECL is considering further testing by taking samples from the vessel wall in order to provide more comprehensive data. Third party corrosion experts have been consulted and will provide feedback.

The Mark II NDE inspection tool has been deployed and inspections have started on the previously inaccessible parts of the vessel.

Investigations are ongoing, however based on evidence collected to date, AECL 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. 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 continues to pursue a second 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.

Guidance on the duration of the shutdown continues to be founded on the best evidence available, including the most up-to-date analysis of the inspection data, progress on repair strategies, and critical path requirements for restart after an extended shutdown. 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. Further guidance on a return to service date will be provided when more data is available.

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.

Evidence collected to date continues to support AECL’s view that the necessary vessel repairs can be made and that NRU will be returned to service.

AECL continues to work very closely with the Canadian Nuclear Safety Commission (CNSC), and CNSC safety inspectors are directly involved at the Chalk River site.

There is no threat to workers, the public, the environment or nuclear safety related to this event. More information on the repair and status updates on the NRU is available at http://www.nrucanada.ca/

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Contact:

Robin Forbes
Manager, External Communications
AECL, 1-866-886-(AECL) 2325