Radiation survey monitoring as a tool during the decontamination of Ontario Hydro reactors

The most recent decontamination of an Ontario Hydro reactor coolant system was carried out in 1989 on Pickering unit 3 (P3) in support of a Large Scale Fuel Channel Replacement program (LSFCR). As a prerequisite to the P3 LSFCR program, there was a firm requirement to reduce reactor face radiation fields of this reactor (already decontaminated once in 1985) to 70mR/h. Greater fields would result in removing workers from the job due to dose limits. This would in turn result in extended outage time due to the loss of worker experience and the need to start over again on the learning curve. Because of the historically high radiation fields observed on P3 and based on experience decontaminating the unit in 1985, a single application of the traditional CANDECON process was not expected to reduce radiation fields to 70mR/h even though sufficient ion exchange resin capacity was available. This required an application of the Alkaline Permanganate (AP) process to condition the stainless steel oxides for removal by a second application of the CANDECON process. The results of the P3 CANDECON/AP/CANDECON reactor coolant system decontamination are presented in this paper including some of the problems experienced during the application of the AP process. Particular emphasis is placed on the decontamination strategy and the use of on-line survey equipment to monitor that strategy. (author)