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Optimization of Monitoring System using Plastic Scintillator for Beta nuclide including Tritium in Water

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Title
Optimization of Monitoring System using Plastic Scintillator for Beta nuclide including Tritium in Water
Author
Lee, UkJae
Advisor
Kim, Hee Reyoung
Keywords
Radiation monitoring; Plastic scintillator; Tririum
Issue Date
2020-02
Publisher
Graduate School of UNIST
Abstract
Various radionuclides can be generated from decommissioning sites and nuclear facilities. Radionuclides can move through water, so monitoring is essential. A monitoring system has been established to detect beta-nuclides in water samples around nuclear facilities. Beta-nuclides, including tritium, have a short range and difficulty in detecting in water samples. In order to solve this problem, the detection chamber of the structure in which the scintillator and the water sample directly contact is designed and constructed. The system is constructed using a plastic scintillator that does not react with water and has a low background level because of its low atomic number. In order to increase detection efficiency, the area of reaction between the water sample and the scintillator is increased by using the multi-layer scintillators structure. Thirteen scintillators are used for low energy beta, such as 3H, and seven scintillators were used for the relatively high energy 90Sr. Using the manufactured detection chamber, an electronics of monitoring system for each nuclide is set. The change of the detection efficiency is confirmed by changing the amplification degree of the main amplifier. The amplification degree of the main amplifier is selected for each case of 3H and 90Sr. The major beta nuclides, 90Sr and 3H nuclides are considered, and the performance of the system is evaluated by the time required to derive the MDA to satisfy regulatory standards for each nuclide. The liquid radioactive effluent level is used for 90Sr and 3H. In case of 90Sr, it takes 18 seconds to satisfy 0.02 Bq/g of effluent level. In the case of 3H, it takes 2,300 seconds to satisfy the standard for effluent level of 40 Bq/g. It is considered that scintillation-based radiation monitoring systems for beta nuclide in water can be used to evaluate effluent level for 3H and 90Sr. The system is expected to be used to ensure the radiological safety of the operating nuclear facilities and decommissioning sites of nuclear power plants.
Description
Department of Nuclear Engineering
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