Abstract
The development of a three-dimensional model of the near-field of ageological repository for spent nuclear fuel is described. The near-fieldcomprises a canister where the spent fuel is enclosed, a layer of bentoniteclay around the canister, a backfilled tunnel over the canister’s depositionhole and finally, the fractured rock adjacent to the bentonite and the tunnel.The main transport processes are diffusion, sorption, radioactive decayand groundwater flow. A mathematical model attempts to couple thewater flow to the mass transport. This model has been simplified to reduceits computational complexity. Our results are compared with the results ofa compartment model obtained from the literature. It is concluded from theagreement between our 3D model and the compartment model, that theresistance approach used in one-dimensional compartment models isrobust enough for use in models for probabilistic risk analysis of long-termperformance of a geological repository.The development of a three-dimensional model of the near-field of ageological repository for spent nuclear fuel is described. The near-fieldcomprises a canister where the spent fuel is enclosed, a layer of bentoniteclay around the canister, a backfilled tunnel over the canister’s depositionhole and finally, the fractured rock adjacent to the bentonite and the tunnel.The main transport processes are diffusion, sorption, radioactive decayand groundwater flow. A mathematical model attempts to couple thewater flow to the mass transport. This model has been simplified to reduceits computational complexity. Our results are compared with the results ofa compartment model obtained from the literature. It is concluded from theagreement between our 3D model and the compartment model, that theresistance approach used in one-dimensional compartment models isrobust enough for use in models for probabilistic risk analysis of long-termperformance of a geological repository.
Highlights
Integrated assessments of repositories for high-level nuclear waste or spent nuclear fuel rely heavily on modelling of the long-term migration of nuclides throughout the engineered barriers of the repository, the geosphere and the biosphere.Assessing the long-term performance of the repository cannot be done without taking into account different types of uncertainties
In this work we present the development of a 3D finite-element model for the near-field of a repository for spent nuclear fuel, and we compare our results with those obtained using the analytic solution of Hedin
SUMMARY AND CONCLUSIONS In recent years, compartment models have been the workhorses of radionuclide transport studies in certain programs of assessments of the long-term performance of geological repositories for spent nuclear fuel
Summary
Integrated assessments of repositories for high-level nuclear waste or spent nuclear fuel rely heavily on modelling of the long-term migration of nuclides throughout the engineered barriers of the repository (near-field), the geosphere (far-field) and the biosphere.Assessing the long-term performance of the repository cannot be done without taking into account different types of uncertainties. Monte-Carlo (probabilistic) methods are very useful for tackling the analysis of uncertainty and they are often used nowadays in risk analyses of nuclear waste. The goal of this work is to access model uncertainty related to the dimensionality of two models of near-field migration (our 3D model versus the 1D model of Hedin [2]). Hedin developed his model to speed up Monte Carlo calculations for risk analyses. Apart from the dimensionality, the main difference between the models is the use of the resistance approach to mass transfer that Hedin introduced in his model. In our work we do not use the resistance approach
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