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 代码系统包括最先进的辐射源项和辐射传输模拟功能，可用于多种应用，包括复杂综合临时存储设施 (CISF) 的剂量率分析。获得许可的 CISF 可用于存储使用各种容器和存储垫设计的商业动力反应堆排放的数万吨乏核燃料。CISF 设计必须符合 10 CFR 第 72 部分提供的监管要求，包括与适用于位于被许可人控制区域之外的真实个人的年度剂量限制相关的要求。因此，计算对公众的剂量是建造 CISF 的许可过程的必要部分。由于 CISF 设计的复杂性和距设施较远距离处的低剂量率，这些计算非常具有挑战性。本文描述了使用 MAVRIC（SCALE 6.2.3 中的蒙特卡罗辐射屏蔽序列）对提议的 CISF 执行的详细远场剂量率计算，并基于离散纵坐标计算自动减少方差。本文中介绍的方法在从源到剂量率的一个步骤中使用了详细的蒙特卡罗辐射传输模拟。使用完整的场地几何形状（所有桶都存在）进行了一系列独立模拟，但只有一个桶包含辐射源，以获得每个存储桶产生的剂量率图。CISF 剂量率图是通过将独立的单个容器模拟产生的剂量率图相加而获得的。计算模型中包含大量超出目标位置以进行剂量率计算的空气和土壤，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敏感性研究，以说明为 CISF 天光剂量率计算选择合适的空气体积、质量密度和成分的重要性。对干燥土壤和含水土壤进行了分析，以确定它们对地面光照辐射的影响。计算模型中包含大量超出目标位置以进行剂量率计算的空气和土壤，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敏感性研究，以说明为 CISF 天光剂量率计算选择合适的空气体积、质量密度和成分的重要性。对干燥土壤和含水土壤进行了分析，以确定它们对地面光照辐射的影响。计算模型中包含大量超出目标位置以进行剂量率计算的空气和土壤，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敏感性研究，以说明为 CISF 天光剂量率计算选择合适的空气体积、质量密度和成分的重要性。对干燥土壤和含水土壤进行了分析，以确定它们对地面光照辐射的影响。