使用済核燃料輸送容器の周辺線量率評価法の研究
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概要
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Present study aims at deriving a simple calculation method by which one can evaluate radiation dose rate around casks in high accuracy with very short calculation time. The method is based on a concept named Radiation Shielding Characteristics of cask wall. Here, the concept is introduced to replace ordinary radiation shielding calculations, which requires a large calculation time and a large core memory of large computers,by a matrix calculation. For the purpose of verifying the accuracy and reliability of the new ,nothod, the method is applied to analysis of measured dose rate distributions around actual casks. Results of analysis revealed that the newly proposed method is excellent in predicting radiation dose rate distributions around casks in high accuracy with short calculation time. The proposed method takes the place of both extreme evaluation methods ordinarily adopted; one is very simple but rough method based on experiences: the other is very fine method based on lengthy radiation shielding calculation codes. The achievement of short calculation time and high accuracy in the proposed method is attained by deviding the whole procedure of ordinary fine radiation shielding calculation into two steps; one is calculation of radiation dose rate on the cask surface by using matrix expression of the characteristic functions: the other is calculation of dose rate distributions by using simple analytical expression of dose rate distributions around casks. Owing to simpleness in calculation procedure of each step, one can easily evaluate dose rate distribution around casks, once source conditions for spent fuels are given. Result of the evaluation is expected to be highly reliable. As an application of the proposed method, a new method is derived for evaluating influence of heterogeneous array effect of spent fuels in different burnup states upon dose rate distribution around casks. This method is shown to be effective for determination of fuel positions as a function of fuel burnup state, if one planns shipping of spent fuels in different burnup states at one time by a cask.
- 1986-01-30