The BR3 PWR is a small nuclear power plant (thermal power 40.9 MWth, net electrical power output 10.5 MWe), designed in the late fifties and started in 1962. It was definitely shut down in 1987. In 1989 the BR3 was selected by the European Union as pilot decommissioning project in the framework of its RTD programme on the decommissioning of nuclear installations. A pre-dismantling decontamination of the reactor primary loop was carried out and allowed to save doses to the operators. The savings are estimated to be up to about 4 to 7 man-Sv. The decommissioning project concerns mainly: • The dismantling of the highly radioactive reactor internals. Different techniques were used and compared on a first actual piece called the thermal shield: from plasma arc torch cutting to mechanical sawing, including also electric discharge machining. Based on the experience gained during this part of the project, the mechanical cutting techniques were promoted for the segmentation of both sets of internals, the desolidarisation and the segmentation of the RPV. • For the dismantling of the reactor pressure vessel, wet and dry dismantling were studied and compared. For economical and feasibility reasons, the wet dismantling was selected. Afterwards, two underwater segmentations were also studied: in-situ segmentation and a segmentation after having removed the RPV out of its cavity. • Mainly for technical reasons, the reactor pressure vessel was removed in one piece out of its cavity in order to be cut in the former refuelling pool. The disconnection of the RPV from the other parts of the plant was followed by the reinstallation of the watertightness of the pool in order to allow remote underwater segmentation. The disconnection, the watertightness reinstallation and the segmentation represented important challenges. The subtasks will be extensively described in the paper: disconnection from the pools floor, removal of the thermal insulation from the legs, decoupling from the primary loop at two levels, from its supporting structure, the reinstallation of the watertightness of the pool and testing, the removal of the RPV out of its cavity, the remote dismantling of its surrounding thermal insulation (which led to an annoying pool water turbidity) and, finally the effective RPV dismantling. • For the segmentation, two main cutting equipments were used: the milling cutter for cutting the RPV into rings and the bandsaw machine for cutting each ring into segments. The bandsaw machine was also used in order to cut the RPV upper flange into pieces vertically as well as horizontally. • The last generated pieces, the highest radioactive ones, were evacuated at the end of 2000. • Waste characterisation, minimization and management is an important part of the task in order to reduce evacuation and storage costs. • ALARA approach was applied from the early beginning of the project. • For each “key operation” cold tests were organized in order to optimize the work and to take benefit of the learning effect of such operation. Results of the operations will be presented, the lessons drawn for the technical choices, dose uptake minimization, waste reduction and the technical problems met will be highlighted. As a pioneering project, the dismantling of the BR3 Reactor Pressure Vessel has shown the technical feasibility of such an operation in a safe and economical way as well.
SCK•CEN is dismantling its small BR3 PWR reactor. For the management of the contaminated loops, we decided first to decrease the dose rate by a chemical decontamination of the circuits. A complete dismantling of the loops and of the equipment’s follows this. After a careful sorting of the pieces, we select the optimised management route, which will lead to a minimum of radioactive waste disposed. This paper gives the results of the management of the pieces arising from the dismantling of the most contaminated loops of the plant. We show that it is possible to recycle most of the metallic materials either in the nuclear world or in the industrial world by reaching the respective recycling or clearance criteria.
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.
Since 1989, SCK•CEN is dismantling the BR3 (Belgian Reactor no3). During these 11 years of decommissioning, a lot of experience is gained in the field of remotely controlled cutting techniques for high active parts and decontamination techniques of highly contaminated parts. Mechanical cutting techniques (circular saw and band saw) were used for cutting the reactor Pressure Vessel (RPV) and its internals. For some large components in the reactor building, like the steam generator, the pressurizer and the Neutron Shield Tank, a new tool, the High Pressure Abrasive Water Jet Cutting will be used to cut activated and contaminated pieces with material thicknesses ranging from 20 to 170 mm. Deliverance of the cutting equipment is foreseen in the summer of 2001. Cold tests and training sessions for the operators will then take place and by the beginning of 2002 the cutting equipment will be installed in the reactor pool inside the controlled area to start the actual work.
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