Radioactive waste may arise throughout the lifetime of any type of nuclear facility. This waste has to be isolated from the environment using the engineered and natural barriers of near surface or deep geological radioactive waste repository. Before final disposal, the waste volume is reduced in the treatment process and then it is immobilized into the stable matrix. In Slovakia, the treated radioactive waste is conditioned into fibre-reinforced concrete containers using a cementation technology. These containers are the only overpacks approved for near surface disposal in the National Radioactive Waste Repository located at Mochovce nuclearsite (Slovakia). Every filled container has to fulfill the defined limits and conditions for safe transport and disposal. The dose parameters, determining the safety of personnel handling a container, are one of them. Basically, the doses are measured on the container walls’ outer surfaces and on the lid of the container. The dose monitoring in 1 meter distance from the container walls and from the lid of the container is performed before transportation as well. The calculation code VISIPLAN 3D ALARA is a planning tool and it calculates dose parameters also for the above mentioned positions concerning the fibre-reinforced concrete container which contains waste with different physical or radiological characteristics. In the paper, calculated data are compared with in-situ measurements. Using VISIPLAN 3D ALARA planning tool, various scenarios are evaluated. Finally, the optimization leading to the lowest radiation exposure of personnel handling the filled fibre-reinforced containers is discussed.
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 nuclear installation decommissioning process is characterized by production of large amount of radioactive materials to be managed. The materials with radioactivity slightly above the unconditional release levels could be released conditionally for a specific industrial application in accordance with beforehand developed and evaluated scenario. This evaluation has to ensure that the limits for radiation exposure of workers and the public will not be exceeded. The paper gives an overview of representative options (scenarios) for reuse of conditionally released steel materials and recycled concrete from decommissioning. The main aim of the paper is to present the developed complex methodology for assessment of these options and its implementation to the relevant calculation tools. The first step in the methodology procedure is the identification of the activities which could lead to the exposure of the public or workers. For defined activities the external exposure of workers and the public is evaluated using the Visiplan 3D ALARA Planning tool. The internal exposure analysis is mainly based on the models for migration of radionuclides in the environment calculated in the GoldSim code. Based on the results of exposure evaluation, the critical exposure pathway is determined and conditional release levels of individual radionuclides are derived. Finally the amount and radioactivity of materials from decommissioning, fulfilling the limits for conditional reuse, are calculated in the decommissioning planning code OMEGA [1].
The nuclear installation decommissioning process is characterized by production of large amount of various radioactive and non-radioactive waste that has to be managed, taking into account its physical, chemical, toxic and radiological properties. Waste management is considered to be one of the key issues within the frame of the decommissioning process. During the decommissioning planning period, the scenarios covering possible routes of materials release into the environment and radioactive waste disposal, should be discussed and evaluated. Unconditional and conditional release to the environment, long-term storage at the nuclear site, near surface or deep geological disposal and relevant material management techniques for achieving the final status should be taken into account in the analysed scenarios. At the level of the final decommissioning plan, it is desirable to have the waste management scenario optimized for local specific facility conditions taking into account a national decommissioning background. The analytical methodology for the evaluation of decommissioning waste management scenarios, presented in the paper, is based on the materials and radioactivity flow modelling, which starts from waste generation activities like pre-dismantling decontamination, selected methods of dismantling, waste treatment and conditioning, up to materials release or conditioned radioactive waste disposal. The necessary input data for scenarios, e.g. nuclear installation inventory database (physical and radiological data), waste processing technologies parameters or material release and waste disposal limits, have to be considered. The analytical methodology principles are implemented into the standardised decommissioning parameters calculation code OMEGA, developed in the DECOM company. In the paper the examples of the methodology implementation for the scenarios optimization are presented and discussed.
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