The paper describes the model application of conditional clearance radioactive demolition waste arising from decommissioning of nuclear power plants and the calculation of individual effective dose absorbed during construction and operation stage of motorway. Large quantities of materials with very low level radioactivity may occur during the decommissioning of NPPs after the end of its lifetime or after a nuclear accident. Part of the decommissioning waste consists of the contaminated demolition waste, which is necessary to be processed and stored on a designated storage sites or disposed. The construction of such stores or repositories requires significant financial and material resources. Possible solving of this issue is conditional clearance of very low level radioactive waste and its reuse in construction of roads, where they are incorporated for 50 to 100 years. This period is necessary for natural radioactive decay of radionuclides to the levels applicable for unconditional clearance. The foundation of a road represents a significant potential for recycling of concrete rubble from the decommissioning. Calculation of external exposure was performed by means of VISIPLAN 3D ALARA, internal exposure due to inhalation was calculated by AMBER 5.4. The outputs of calculations are the individual effective dose absorbed during working activities from all relevant exposure pathways. Final results include clearance levels -specific mass activities of demolition waste designated for clearance.
Paper presents the overall scope and actual results of the project for evaluation of representative scenarios for reuse of conditionally released materials from decommissioning. Aim of the project is to evaluate the possibilities of reuse of conditionally released steels and concrete in technical constructions which guarantee the long-term preservation of design properties over periods of 50–100 years. Interaction of conditionally released materials with public is limited and predictable due to design and purpose of selected constructions and due to fact that in many scenarios these materials are embedded in non-radioactive materials such as bars in reinforced concrete. Worker’s scenarios for preparation, operation and maintenance of these constructions are analysed in detail including the manufacturing of elements for these constructions. Project aims to evaluate the scenarios of reuse of conditionally released materials in a complex way in order to develop the data for designers of scenarios and to evaluate the volumes of conditionally released materials based on facility (to be decommissioned) inventory data. The long-term constructions considered are bridges, tunnels, roads, railway constructions, industrial buildings, power industry equipment and others. Evaluation covers following areas: • Analysis of activities for manufacturing of reinforcement bars, rolled steel sheets and other steel elements and analysis of activities for construction of evaluated scenarios in order to evaluate the external exposure of professionals performing these activities; • Analysis of external exposure of professionals involved in operation and maintenance of the long-term constructions; analysis of external exposure of public groups which are exposed to evaluated constructions; • Analysis of internal exposure of public groups from the radionuclides released from the evaluated scenarios based on models for migration of radionuclides from the long-term constructions to critical groups of public; • Based on evaluation of external and internal exposure both for public and workers, maximal concentration of individual radionuclides is defined for construction elements of evaluated scenarios, manufactured from conditionally released materials; • Evaluation of volumes of steels and concrete in the frame of a decommissioning project which fulfil the defined radioactivity concentration limits. Visiplan 4.0 3D ALARA software is used for evaluation of external exposure of professionals and public, GOLDSIM software for evaluation of internal exposure of public and OMEGA code for evaluation of volumes of conditionally releasable materials. Several other parallel papers proposed for ICEM 11 are presenting selected details of the project.
The paper deals with the conditional release of low-level radioactive steel from decommissioning in a form of reinforced concrete. The main goal was to determine limits for radionuclides concentration and calculate the annual dose for a member of a critical group of public, which should not exceed 10 μSv/year (according to IAEA Safety Guide RS-G-1.7). Corrosion is the principle mechanism of radionuclides release in this case; therefore effort was devoted to assess the time-dependent rate of steel reinforcement corrosion. It was assumed, that concrete is initially highly alkaline (with pH of 12 to 13) because of hydration products such as calcium hydroxide, which keeps the steel surface passive and protected from corrosion. However, carbonic acid resulting from carbon dioxide and water in the atmosphere can react with these products to produce calcium carbonate. This process is referred to as a “carbonation”, and leads after a period of time to significant reduction of the alkalinity (to pH as low as 8.5) followed by destruction of passive layer and starting corrosion of the embedded steel. The analytical principles and a set of input data have been implemented into a mathematical model developed by means of GoldSim software. The paper presents the results of mathematical simulation of corrosion process, which are compared with real measured values.
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