IN-SITU GAMMA-SPECTROMETRY OF PIPING IN A CANDU HEAT-TRANSPORT SYSTEM- APPLICATION DURING DECONTAMINATION

An in situ pipe gamma spectrometry technique was applied to determine the activity within piping during various stages of CANDU reactor deco ntaminations. Measurements were performed in general radiation fields up to similar to 500 mR/h and required both the detector and the pipe being scanned to be appropriately shielded from other neighboring pipi ng. Measured counts were interpreted using a pipe source efficiency ca libration with due regard to its distance dependence. Cobalt-60 was th e dominant radionuclide on the piping before the decontamination. Depo sition of Sb-124 occurred on out-core piping surfaces during the decon tamination. The spectrometry measurements were supplemented with conta ct radiation field measurements, which were performed using survey def ectors housed within specially designed pipe shields. Radiation fields estimated from measured radionuclide activities were compared with th e measured radiation fields. On average, the ratio of measured to esti mated fields was similar to 72%. Reasons for this discrepancy are disc ussed.