The decommissioning of the BR3 (Belgian Reactor 3) approaches its final phase, in which the building structures are being decontaminated and either denuclearized for possible reuse or demolished. Apart from the presence of naturally occurring radionuclides in building materials, other radionuclides might be present due to contamination or activation. The overall process of the BR3 building structure D&D (Decontamination & Decommissioning) consists of the following steps: • make a complete inventory and preliminary categorize all elements based on historical data; • characterize and determine the contamination or activation depth; • determine the decontamination method; • perform the decontamination and clean up; • a possible intermediate characterization followed by an additional decontamination step; and • characterize for clearance. A good knowledge of the contamination and activation depth (second step) is fundamental in view of cost minimization. Currently, the method commonly used for the determination of the depth is based on core drilling and destructive analysis. Recently, we have introduced a complementary non destructive assay based on in-situ gamma spectroscopy. Field tests at BR3, both for contamination and activation, showed promising results.
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.
Liquid as well as solid organic radioactive waste can be processed by means of combustion. However, this method presents several well-known drawbacks including the corrosion of the ovens, the production of radioactive ashes and radioactive or toxic volatile products. The electrochemical mediation process is an excellent alternative to combustion, especially when dealing with hazardous materials such as explosives, pesticides, drugs and nuclear organic waste. Nevertheless, using the silver(II) species as electrogenerated mediator, requires to work in concentrated nitric acid media, which results, via its electrolysis, in a continuous NOx emission. The classical approach, using absorption columns and scrubbers to trap NOx, impairs the attractiveness of this process. Therefore the SCK•CEN has developed and patented an original method to suppress in-situ any formation of NOx, conferring the process mobility and compactness.
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