Fuel Channel Inspection a Rewarding Experienceby Jeremy Whitlock
Chaplin, a resident of Deep River, described the events leading up to the Romanian trip. AECL has three decades of experience in CANDU channel inspection. CANDU channels contain the pressurized coolant and the fuel, and therefore their inspection during and after a reactor's commissioning is a license requirement.
Among the characteristics requiring inspection are overall channel length, sag, diameter, garter-spring location, surface flaws, and other signs of wear-and-tear. Usually an inspection is required every few years in order to certify the safe operation of the reactor for a prescribed operating period.
Until recently AECL's expertise was strictly in "dry" channel inspection, requiring that the channel of interest be empty of coolant. Ontario Hydro developed a "wet" inspection system that dispensed with this requirement, and marketed its inspection services to CANDU utilities world-wide. By the time Romania came along with its request, however, Ontario Hydro was out of the commercial inspection business.
AECL took up the opportunity, and in August 1998 began development of its own "wet" channel inspection system. The requirements were daunting. A compact, submersible inspection head with an array of ultrasonic, eddy current, and mechanical sensors must map the entire inner surface of a pressure tube, and function properly under intense pressure and irradiation.
The software that operates the system and collects the hundreds of megabytes of data per channel also had to be developed. This was particularly challenging, Chaplin notes, in a year when many software experts were drawn away to fight the Y2K bug.
Nevertheless, a year later AECL had a demonstration ready for the Romanians, and two months later the system and its team of eleven field operators were on their way to the Cernavoda plant to perform their first inspection.
What followed was a month of grueling 10-14 hour shifts for the AECL team members, working closely with counterparts from the Romanian electrical utility. The schedule included two weeks of preparation, training, and testing, followed by two weeks of operation. Working inside the reactor vault was particularly noisy and stressful.
Chaplin reported that the mission was successful, despite many teething problems and hard lessons learned. The tonnes of equipment are now back in Chalk River, requiring some decontamination and no doubt a bit of re-tooling. A "Mark 2" version will soon be ready for AECL's next commercial inspection, and subsequent jobs for are expected to start bringing in revenue for the company at least once a year.