In the process of decommissioning of nuclear facilities there is produced a lot of material with various levels of radioactivity. Large portion of the material could be conditionally cleared as an alternative to the treatment and disposal of this material as radioactive waste. Idea of conditional clearance is to facilitate the reuse of material with the radioactivity slightly above legislation limits of specific activity valid for unconditional clearance into the environment keeping dose criteria for the public. The radiation impact of cleared materials can be divided into short-term and long-term impact. Long-term radiation impact consists of inhalation or ingestion of radionuclides and external irradiation from the contaminated soil or dust. Transport of radionuclides from the conditionally cleared materials through the subsoil or waterways and subsequent intake of these radionuclides by humans was simulated and calculated using GOLDSIM software. Calculated models represent situations and geometries of the most probable future applications of conditionally cleared materials in building constructions. Output parameters are the clearance levels of radionuclides in conditionally cleared materials relevant to the legislation dose criteria (10 or 50 µSv/year) -the maximum clearable specific activity of radionuclides in the material from the dose point of view.
This paper presents ongoing results of the project presented at ICEM’10 [1] related to the topics of reusing the conditionally released materials from decommissioning. The subject of the reuse of conditionally released materials in this case is modeling of bridge constructions which reuse the conditionally released steel in the form of reinforcement bars for the concrete bridges. A general approach for the project was presented at ICEM’10. The activities of the project continue in evaluating the individual effective doses from the external exposure based on reused conditionally released steels separately for public and for professionals (the internal exposure will be evaluated in next stages of the project). Evaluated scenarios are related to critical groups of professionals constructing the bridges (worker’s scenarios). The computer code VISIPLAN 3D ALARA 4.0 planning tool was used for the calculation of the individual effective dose for professionals. Various limits of the annual individual effective dose are used for the evaluation of calculation results. The aim of the ongoing modeling is to develop a set of data of maximal radioactivity concentration for individual radionuclides in the conditionally released steel used in the bridges model constructions in order not to exceed the limits for the individual effective dose.
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