The dismantling of the BR3-PWR reactor leads to the production of large masses of contaminated metallic pieces, including structural materials, primary pipings, tanks and heat exchangers. One of the main objectives is to demonstrate that we can minimise the volume of radioactive waste in an economical way, by the use of alternative waste routes, such as recycling of material in the nuclear world, free release of material in the conventional industry after melting or free release of material after thorough decontamination. The SCK•CEN launched a decontamination program with the aim to free release as much of the dismantled metallic material as possible. The selected chemical decontamination process, so-called MEDOC® (MEtal Decontamination by Oxidation with Cerium), is based on the use of cerium IV as strong oxidant in sulphuric acid with continuous regeneration using ozone. An industrial installation has been designed and constructed in close collaboration with Framatome-France. This installation started to operate in September 1999 for the treatment of the metallic pieces arising from the dismantling of the BR3 reactor. Since the installation starts up, 21 tons of contaminated material has been treated batchwise with success. Up to now, MEDOC® has been accomplished as a batch process in which the decontamination reactor is loaded with a basket containing the contaminated material. The SCK•CEN is now considering the possibility of using the MEDOC plant to decontaminate large components before cutting them, such as the BR3 -steam generator and the pressurizer. The decontamination solution will be circulated between the MEDOC plant and the steam generator during the consecutive decontamination cycles. Each cycle will comprises a decontamination step followed by a regeneration step. For the steam generator, 30 cycles are estimated to be needed to reach the free release level after melting. The decontamination studies of large components are ongoing and take into account the technical aspects, the radiological and classical safety aspects, as well as financial aspects.
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.
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