An optimized strategy for the management of spent steam generators

The decommissioning of the BR3 (Belgian Reactor 3) approaches its final phase. The electro-mechanical dismantling is almost completed and the program related to the decontamination of the building structures has been initiated. The issue of the evacuation of the primary circuit large components, and more specifically of the Steam Generator (SG), has been dealt successfully, applying innovative technologies to lead to remarkable results in terms of waste volume minimization and occupational radiation exposure. The strategy applied for the evacuation of the BR3 SG resulted from the elaboration and comparison of the following scenarios : • Closed loop chemical decontamination prior to dismantling, cutting and unconditional release or release after melting, • Cutting of the components without decontamination and evacuation of the materials in their respective waste categories, • Cutting, decontamination of the SG secondary side and evacuation of the full SG primary side to the melting facility for recycling. While the availability of the in-house developed MEDOC® process made the clearance of the SG bundle technically feasible, nuclear safety requirements and financial aspects were also in favour of the closed loop decontamination: minimization of contamination spreading and staff exposure during all subsequent manipulations, minimization of radwaste costs. For the segmentation of this component, different techniques have been considered : • An abrasive water jet (AWJ) cutting tool, • A prototype diamond wire developed for this application. The diamond wire allowed to cut in a single pass both the carbon steel shell and the stainless steel tube bundle. While the implementation of the diamond wire saw is rather simple, working conditions must be optimised to limit wearing of the wire and secondary waste production. Existing experience can be extrapolated to different legal frameworks in order to propose a financially and technically optimised "all-in" strategy for the management of "spent" SG.