Abstract
Abstract Accurate dose rate models for UO2 based materials in contact with water are important in the modeling of the radiolytically promoted dissolution of spent fuel. Dose rates of α-doped UO2 and un-irradiated MOX fuel were modelled using the ASTAR and SRIM stopping power databases. Dose rates were calculated as a function of distance from the active surface. Comparisons with common dose rate calculation models and the combined Bethe-Bloch and Lindhard–Scharff (LS) equation were performed. It was shown that the ASTAR and SRIM databases could more accurately simulate an α-spectrum compared to the Bethe-Bloch-LS equation. A comparison between the continuous slowing down approximation (CSDA) and the radial projection algorithm in the SRIM program was performed, and it was shown that CSDA overestimates the range of the α-particles by a few percent. This leads to an overestimation of the α-dose rate at distances close to the maximum range of the α-particle in water. A relationship between the average dose rate to specific α-activity ratio as a function of α-energy was obtained from the calculations, which can easily be implemented in alpha dose rate calculations of a UO2 based materials.
Highlights
In the safety analysis of a geological repository, the oxidative dissolution of the used nuclear fuel in case of a water intrusion scenario determines the source term from the repository
All water stopping power curves show a Bragg-peak characteristic of charged particles. Both ASTAR and SRIM show a Bragg-peak in UO2, but the Bethe-Bloch-LS equation does not show this tendency
Based on the region of validity of the Bethe-Bloch equation, the equation seems unsuitable for describing the attenuation of α-particles in the α-energy spectrum relevant for nuclear fuel
Summary
In the safety analysis of a geological repository, the oxidative dissolution of the used nuclear fuel in case of a water intrusion scenario determines the source term from the repository. As UO2 is highly insoluble in the U(IV) state, the dissolution rate is negligible under the reducing groundwater conditions [2]. This is due to reducing minerals present at final repository depths (~500 m) [3]. The main mechanism of fuel dissolution is through the formation of locally oxidizing conditions at the fuel surface through radiolysis of water [4]. The production of radiolytic oxidants depends on the type of radiation and on the dose rate. Alpha radiolysis persists during long repository times and is the main contributor to fuel dissolution after a thousand years. Recent results [6, 7] indicate that a large amount of H2O2 decomposes to oxygen and water on the fuel surface, thereby slightly decreasing the importance of H2O2 for SIMFUEL in favor of O2 [8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
