Tecnubel has recently performed various chemical decontamination of French and Belgian Pressurized Water Reactors (PWR) systems and components. The purpose of this paper is to present and compare these experiences. The objectives of these operation were the reduction of the general surface contamination together with the elimination of hot spots in Residual Heat Removal Systems (RHRS), Chemical and Volume Control Systems (CVCS) and Reactor Coolant Pumps (RCP). This reduction of contamination leads to the reduction of dosimetry to the maintenance personnel and allows the works on critical equipment. An additional challenge for three of these projects lay in the execution of a complicated operation on the critical path of a reactor refueling shutdown. The chemical decontamination were performed by circulating an adequate fluid in the systems or around the components. Since the contamination was generated at hot conditions during power operation, a redox attack on the surface was necessary. The EDF systems and components were decontaminated using a qualified EDF process of the EMMAC family. The Reactor Coolant Pump from the Belgian PWR was treated with the NITROX process, qualified by Westinghouse. The functions required by the decontamination system were very diverse and therefore an existing decontamination loop, which was previously developed for the decontamination of small circuits, was re-developed and adapted for bigger volumes by DDR Consult and Tecnubel. The results of five decontamination are presented and detailed in terms of efficiency and waste production. These projects were: the chemical decontamination of the RHRS of Flamanville 1 NPP, of the CVCS non regenerative heat exchanger at St Laurent des Eaux NPP, of the RHRS and CVCS of Bugey 2 NPP and of two RCP at the Westinghouse Belgian Service Center.
<p>The Republic of Serbia wishes to evaluate the various options for disposal of radioactive waste and used sources. The evaluation is supposed to be based on international solutions for radioactive waste, the current and future waste inventory of Serbia, and the various possible solutions for final disposal. A high-level assessment of the geological situation in Serbia, as well as an initial screening for suitable host rock material, is inherently included in such an evaluation, and is the aim of the current work.</p><p>Based on available information such as orohydrographical and morphostructural maps, the 1:300.000 geological map, individual but undisclosed 1:100.000 geological mapsheets, the 1:500.000 neo-Alpine tectonic map of Serbia, seismic hazard maps for different return periods, and various scientific publications dealing with the geological and tectonic evolution of Serbia and surroundings, several initial recommendations can be formulated that will support and assist the decision-making process in finding a suitable site (and host rock).</p><p>Roughly, the territory can be divided into two different regions with contrasting tectonic behaviour. South of the Danube, the relief intensity is significant and mountain massives with altitudes up to 2000 m and more are present. The most important morphostructural units include the Dinarides, the Vardar Zone, the Serbo-Macedonian Massif and the Carpatho-Balkanides. This region is characterised by outcropping and subcropping material that underwent significant deformation during various tectonic pulses in the past, resulting in a vast area with rather impermeable meta-sedimentary and metamorphic rocks. Neo-Alpine tectonics from the Oligo-Miocene onwards resulted in significant vertical uplift of the southern massifs, this pattern being interrupted by isolated and closed subsiding depressions. Throughout the region south of the Danube, magmatic rocks of various age, type and composition can be found, which are elsewhere being considered in international solutions for geological disposal. The same is valid for the previously mentioned meta-sedimentary and metamorphic rocks, which include flysch sequences, and several schist and gneiss occurrences.</p><p>North of the Danube, the Pannonian Basin is characterised by significant subsidence, up to several thousand meters since the Oligo-Miocene. The basin is filled with continental clastic deposits, with several prominent clay occurrences of sufficient thickness and depth. Clay rock and (plastic) unlithified clay are often being considered in international solutions for geological waste disposal.</p><p>The neo-Alpine tectonic map indicates the presence of numerous faults: gravitational, reverse and strike-slip. Quite a number of these have shown significant activity in the Pliocene and Quaternary, most notably those that mark the boundary between outcropping massifs and subsiding areas (e.g., between the Carpatho-Balkanides and the marginal part of the Pannonian Basin). Near those faults, historical seismic activity has been recorded with magnitudes up to M = 6.5. Seismic hazard seems to be highest in the central and southern part of the country.</p><p>In summary, this short geological reconnaisance of Serbia suggests that basic geological knowledge is available that will help evaluating the various disposal options, both in terms of host rock material (thickness and depth) and a stable geological environment.</p>
A sump in the RPE circuit in the EDF - Nuclear Power Plant of Cruas-Meysse, showed an extremely high radiation dose rate since 2007. Different attempts to decontaminate the sump did not have the desired effect. The sump is a so-called “gatte” where two flows of different fluida circulates. A chemical flow transverses the sump within stainless steel piping, the second flow which is (contaminated) residual water, flows through this sump in contact with the sumps walls. The dose rate was estimated at 20 Sv/h, and it was presumed being a single hotspot in the dead zone of the sump, where no chemicals from the chemical decontamination attempts and no high pressure water contact had been possible, or had any effect. To protect the maintenance and exploitation people from the radiation, the sump had been protected with a physical protection system, named a sarcophagus. The client asked to leave this protection system, which was modular, on place during the dismantling works to assure its radiation protection function. The paper describes the remote controlled dismantling of the sump within the particular running conditions of the power plant, the developments made to the equipment, and the conditions in which the works had to be carried out. Some lessons learnt and particular points of attention are revealed to complete this paper.
Safe decontamination is a regular requirement in the lifecycle of a nuclear plant and is integral to the careful maintenance of any nuclear installation for 4 key reasons: • To decrease the risk of radioactive contamination spreading • To limit the radioactive doses contracted by maintenance personnel • To limit the radioactive doses incurred during decommissioning • To downgrade the class of radioactive waste The primary goal of decommissioning is to remove aged and/or contaminated and/or activated components of an installation, safely and securely, in as short a time as possible. There are several reasons why this may be necessary: • To eliminate the risk of radioactive contamination spreading • To eliminate the risk of radiation • To downgrade a site or a circuit to a point where it no longer is submitted to regular inspection • To remove installations or parts that are no longer in service or have aged There are many different D&D techniques, tools and materials available today. What is important is knowing how best to use them. This paper describes the experiences and the future projects of Tecnubel in D & D projects in Belgium and abroad.
The purpose of the decontamination of the RHRS at Flamanville 1 was the reduction of the general dosimetry and the elimination of hot spots. This was done to allow the maintenance on the RHRS equipment. The main challenge of this project was the execution of a complicated operation on the critical path of a shutdown. The redox attack of the oxides at the surface of the circuit in Flamanville, was performed by an EDF qualified process of the EMMAC family. The functions required by the decontamination system were very diverse and therefore an existing decontamination loop, which was previously developed for the decontamination of small system volumes, was re-developed and adapted for bigger circuits. Due to different reasons, an important delay on the planning happened. Therefore, only one cycle EMMAg was performed, totalling 2 hours of decontamination. Despite this, a DRRF (dose rate reduction factor) of 3,7 average was reached. The re-designed equipment and a shortened process were validated during this project. An acceptable DRRF was reached with no delay on the critical path. The capability of maintenance on the RHRS equipment is recovered with a gain of factor 5 on dosimetry.
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