The value of simplified models of radionuclide transport for the safety assessment of nuclear waste repositories: A benchmark study

IF 3.5 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES
Philipp Selzer , Haibing Shao , Christoph Behrens , Christoph Lehmann , Robert Seydewitz , Renchao Lu , Phillip Kreye , Wolfram Rühaak , Olaf Kolditz
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引用次数: 0

Abstract

In order to assess sites for a deep geological repository for storing high-level nuclear waste safely in Germany, various numerical models and tools will be in use. For their interaction within one workflow, their reproducibility, and reliability version-controlled open-source solutions and careful documentation of model setups, results and verifications are of special value. However, spatially fully resolved models including all relevant physical and chemical processes are neither computationally feasible for large domains nor is the data typically available to parameterize such models. Thus, simplified models are crucial for the pre-assessment of possible sites to narrow down the list of suitable candidates for which detailed site investigations and fully resolved models will be done at a later stage. Still, the accuracy of these simplified models is of importance as the pre-assessment of suitable sites will be based on them. In this study, we compare the modelling capabilities of TransPyREnd, a one-dimensional transport code based on finite differences, specifically developed for the fast estimation of radionuclide transport by the German federal company for radioactive waste disposal (BGE), with OpenGeoSys, which is a modelling platform based on finite elements in up to three spatial dimensions. Both codes are used in the site selection procedure for the German nuclear waste repository. The comparison of the model results of TransPyREnd and OpenGeoSys is augmented by comparisons with an analytical solution for a homogeneous material. For the purpose of numerical benchmarking, we consider a geological profile located in southern Germany as an example where the hypothetical repository is located in a clay-stone formation. TransPyREnd and OpenGeoSys yield overall similar results. However, both codes use different discretizations which impact is the highest for strongly sorbing compounds, while the difference gets negligible for less sorbing and more diffusive compounds as higher diffusion tends to blur the initial conditions. Overall, the OpenGeoSys model is more exact whereas the TransPyREnd model has considerable faster run times. We found in our example, that significant substance amounts are only leaving the host rock formation, if apparent diffusion is high, for which case both codes give similar results, while relative differences are considerable for strongly sorbing compounds. However, in the latter case no significant substance amount of radionuclides leaves the host-rock formation, thus deeming the differences in the model results minor for the overall safety assessments of sites.

放射性核素迁移简化模型对核废料储存库安全评估的价值:基准研究
为了评估德国安全储存高浓度核废料的深层地质处置库选址,将使用各种数值模型和工具。为了在一个工作流程中实现互动、可重现性和可靠性,版本控制的开源解决方案以及对模型设置、结果和验证的仔细记录具有特殊价值。然而,包括所有相关物理和化学过程在内的空间全解析模型,对于大面积区域来说,既不具备计算可行性,也不具备参数化此类模型的典型数据。因此,简化模型对于预先评估可能的场址至关重要,可缩小合适候选场址的范围,以便在稍后阶段进行详细的场址调查和建立完全解析的模型。不过,这些简化模型的准确性也很重要,因为对合适地点的预评估将以这些模型为基础。在本研究中,我们比较了 TransPyREnd 和 OpenGeoSys 的建模能力,前者是基于有限差分的一维传输代码,专门为德国联邦放射性废物处理公司(BGE)快速估算放射性核素传输而开发,后者则是基于有限元的三维建模平台。这两种代码都用于德国核废料处置库的选址程序。在对 TransPyREnd 和 OpenGeoSys 的模型结果进行比较的同时,还与均质材料的分析解决方案进行了比较。为了进行数值基准比较,我们以德国南部的一个地质剖面为例,假定处置库位于粘土石层中。TransPyREnd 和 OpenGeoSys 得出的结果总体类似。不过,这两种代码使用了不同的离散化方法,对于强吸附性化合物的影响最大,而对于吸附性较弱和扩散性较强的化合物,差异可以忽略不计,因为较高的扩散性往往会模糊初始条件。总体而言,OpenGeoSys 模型更为精确,而 TransPyREnd 模型的运行时间要快得多。我们在示例中发现,只有在表观扩散程度较高的情况下,才会有大量物质离开主岩层,在这种情况下,两种代码给出的结果相似,而对于吸附性较强的化合物来说,相对差异较大。不过,在后一种情况下,没有大量放射性核素离开主岩层,因此模型结果的差异对于场地的整体安全评估来说是微不足道的。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of contaminant hydrology
Journal of contaminant hydrology 环境科学-地球科学综合
CiteScore
6.80
自引率
2.80%
发文量
129
审稿时长
68 days
期刊介绍: The Journal of Contaminant Hydrology is an international journal publishing scientific articles pertaining to the contamination of subsurface water resources. Emphasis is placed on investigations of the physical, chemical, and biological processes influencing the behavior and fate of organic and inorganic contaminants in the unsaturated (vadose) and saturated (groundwater) zones, as well as at groundwater-surface water interfaces. The ecological impacts of contaminants transported both from and to aquifers are of interest. Articles on contamination of surface water only, without a link to groundwater, are out of the scope. Broad latitude is allowed in identifying contaminants of interest, and include legacy and emerging pollutants, nutrients, nanoparticles, pathogenic microorganisms (e.g., bacteria, viruses, protozoa), microplastics, and various constituents associated with energy production (e.g., methane, carbon dioxide, hydrogen sulfide). The journal''s scope embraces a wide range of topics including: experimental investigations of contaminant sorption, diffusion, transformation, volatilization and transport in the surface and subsurface; characterization of soil and aquifer properties only as they influence contaminant behavior; development and testing of mathematical models of contaminant behaviour; innovative techniques for restoration of contaminated sites; development of new tools or techniques for monitoring the extent of soil and groundwater contamination; transformation of contaminants in the hyporheic zone; effects of contaminants traversing the hyporheic zone on surface water and groundwater ecosystems; subsurface carbon sequestration and/or turnover; and migration of fluids associated with energy production into groundwater.
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