Recent decontamination experiences in BWRs and the effect of operational water chemistry on the decontamination application

OKG owns and operates three nuclear power plants designed by ABB - Atom at the Simpevarp site on the Swedish east coast. Oskarshamn 1, a 495 MWe BWR, was taken in commercial operation in 1972, operating with normal water chemistry (NWC) and zinc injection since 2003. Oskarshamn 2, a 630 MWe BWR, taken in commercial operation in 1974, initially operating with normal water chemistry. Hydrogen water chemistry operation (HWC) started in 1992 and zinc injection (DZO) started in October 2003. Oskarshamn 3, a 1450 MWe BWR, taken in commercial operation in 1985, and until today operating with NWC. The Residual Heat Removal System (RHR) and the Reactor Water Cleanup system (RWCU) of all the three plants were decontaminated with the AREVA decontamination process CORD^®. In Oskarshamn 2 the system was decontaminated in 2003, prior to the start of zinc injection and once again in 2013 after nearly 10 years of the application of HWC and DZO. The decontamination in 2013 was performed, in order to reduce the collective radiation exposure of the outage personnel, prior to the massive refurbishment work during the execution of the Plant Lifetime Extension Project PLEX. During the decontamination application in 2013, it was noticed that the dose reduction was not achievable with the same chemical application of 3 CORD^® cycles, as in the previous applications. This resulted in an increase in the number of application cycles to achieve the same reduction of dose levels as in 2003. This paper discusses the oxide characteristics due to the different operational water chemistry and the effect of changes of the oxide nature on the decontamination application. It compares recent similar decontamination applications in the Swedish BWR Plants at Oskarshamn applying different operational water chemistry. Results are reported in this contribution. (author)