Abstract

The SCALE code system developed at Oak Ridge National Laboratory includes state-of-the-art capabilities for radiation source term and radiation transport simulations that can be used in numerous applications, including dose rate analyses of complex consolidated interim storage facilities (CISFs). A licensed CISF could be used to store tens of thousands of tonnes of spent nuclear fuel discharged from commercial power reactors using various cask and storage pad designs. A CISF design must comply with the regulatory requirements provided in 10 CFR Part 72, including requirements related to annual dose limits applicable to real individuals located beyond the area controlled by the licensee. Therefore, calculating a dose to the public is a necessary part of the licensing process for the construction of a CISF. These calculations are very challenging because of the complexity of the CISF design and the low magnitude of dose rate at large distances from the facility. This paper describes detailed far-field dose rate calculations performed for a proposed CISF using MAVRIC, the Monte Carlo radiation shielding sequence in SCALE 6.2.3, with automated variance reduction based on discrete ordinates calculations. The method presented in this paper uses a detailed Monte Carlo radiation transport simulation in one step from source to dose rate. A series of independent simulations was made using the complete site geometry (all casks present), but with only one cask containing radiation sources to obtain the dose rate maps produced by each storage cask. The CISF dose rate map was obtained by adding the dose rate maps produced by the independent individual cask simulations. Ample volumes of air and soil extending beyond the location of interest for dose rate calculation were included in the calculation model to properly simulate important radiation attenuation and scattering events that affect far-field dose rates. A comprehensive sensitivity study is included in this paper to illustrate the importance of selecting appropriate air volume, mass density, and composition for CISF skyshine dose rate calculations. Dry soil and soil containing water were analyzed to determine their effects on groundshine radiation.

摘要

橡树岭国家实验室开发的SCALE代码系统包括用于辐射源项和辐射传输模拟的最新功能，可用于多种应用，包括复杂的综合临时存储设施（CISF）的剂量率分析。可以使用获得许可的CISF，使用各种桶和存储垫设计来存储从商业动力反应堆中排放的数万吨废核燃料。CISF设计必须符合10 CFR第72部分中提供的法规要求，包括与适用于位于被许可方控制范围之外的真实个体的年度剂量限值有关的要求。因此，计算向公众的剂量是建造CISF的许可过程的必要部分。这些计算非常具有挑战性，因为CISF设计的复杂性以及与工厂距离较远时的剂量率低。本文介绍了使用MAVRIC（SCALE 6.2.3中的蒙特卡罗辐射屏蔽序列）对拟议CISF进行的详细远场剂量率计算，并基于离散坐标计算自动减少了方差。本文介绍的方法在从源到剂量率的一步中使用了详细的蒙特卡洛辐射传输模拟。使用完整的站点几何结构（存在所有桶）进行了一系列独立的模拟，但是只有一个包含辐射源的桶才能获得每个存储桶产生的剂量率图。CISF剂量率图是通过添加独立的独立桶模拟生成的剂量率图获得的。计算模型中包括了超出目标位置以进行剂量率计算的大量空气和土壤，以正确模拟影响远场剂量率的重要辐射衰减和散射事件。本文包括一项全面的灵敏度研究，以说明选择合适的空气量，质量密度和组成对于CISF天窗剂量率计算的重要性。分析了干燥的土壤和含水的土壤，以确定它们对地面光辐射的影响。计算模型中包括了超出目标位置以进行剂量率计算的大量空气和土壤，以正确模拟影响远场剂量率的重要辐射衰减和散射事件。本文包括一项全面的灵敏度研究，以说明选择合适的空气量，质量密度和组成对于CISF天窗剂量率计算的重要性。分析了干燥的土壤和含水的土壤，以确定它们对地面光辐射的影响。计算模型中包括了超出目标位置以进行剂量率计算的大量空气和土壤，以正确模拟影响远场剂量率的重要辐射衰减和散射事件。本文包括一项全面的灵敏度研究，以说明选择合适的空气量，质量密度和组成对于CISF天窗剂量率计算的重要性。分析了干燥的土壤和含水的土壤，以确定它们对地面光辐射的影响。