Defective fuel location by dry sipping

One of the largest fuel defect excursions experienced by Ontario Hydro occurred in Unit 3 of Bruce NGS-A during December 1983 and early 1984. A large part of our response to this problem involved the underwater visual examinations of irradiated fuel bundles. We were able to greatly reduce our workload by monitoring the radioactivity released by defected fuel bundles during their dry transfer from the D2O of the fueling machine to the H2O of the irradiated fuel bay (IFB). This procedure is commonly called 'dry sipping'. We were very successful in correlating dry sipping indications from a suspect bundle pair to visually confirmed defected bundles. Residual contamination in the active vent of the fuel transfer system, after discharge of fuel to the IFB, almost always indicated discharge of a defected bundle. This was a new observation. The short lived activity spike in the vent, during the discharge, was not found to be as reliable an indicator. This successful experience contributed significantly to the resolution of the fuel defect problem. Also, the automatic system we installed greatly reduced the radiological hazard to station staff from the manual dry sipping procedure that existed previously. These results promise useful applications to other Ontario Hydro nuclear stations