Characterization and Decontamination of a Reactor Artefact from a Decommissioned Boiling Water Reactor

Abstract

Corrosion of system components occurs during reactor operation, leading to the formation of various types of corrosion products. While magnetite (Fe₃O₄) is the predominant oxide formed on 3 4 surfaces in the primary heat transport system of a CANDU reactor, deposits formed in a Boiling Water Reactor (BWR) are different, primarily due to the use of different alloys and operating chemistries. When in-core deposits are exposed to a neutron flux, they become activated and may subsequently be dissolved, transported and re-deposited on out-of-core material surfaces. Radionuclides present in the coolant can be incorporated in oxide surfaces and result in an increase in radiation fields around the piping; consequently, dose to workers occurs during maintenance activities, such as refurbishment for reactor life extension or decommissioning. In this work, an artefact removed from the Reactor Water Clean Up system of a permanently shutdown BWR was characterized and decontaminated using two reducing decontamination processes, i.e., CAN-DEREM™ and CAN-DEREM Plus™. Chemical analyses of surface oxides using X-ray diffraction indicated the presence of hematite (α-Fe₂O₃ ). X-ray fluorescence analysis of the substrate indicated that the artefact was made of 316 stainless steel (SS). Gamma (γ) spectroscopic analyses of surfaces showed that the major γ-emitters were ⁶⁰Co, ⁹⁴Nb, ¹³⁷Cs, and ²⁴¹Am. Decontamination factors of 5.9 and 10.6 were achieved using CAN-DEREM and CAN-DEREM Plus processes, respectively. Future testing of the artefact is in progress to optimize process effectiveness.