2021:20 Effects of additives on UO2 fuel behavior: expanded edition

SSM perspective

Background

The Swedish Radiation Safety Authority (SSM) follows the development of nuclear fuel closely. Fuel with additives like chromia and gadolinia is used in Swedish reactors and fuel with even better thermal and mechanical properties is under development. This project is an in-depth study of data and models regarding the impact of additives on the properties of uranium dioxide fuel for light water reactors. The report is an update and expansion of the study of additives for uranium dioxide pellets that Quantum Technologies AB conducted for SSM in 2013 (SSM report 2014:21).

Results

The project constituted a review of recently completed and published experiments and studies as well as a review of computational models that describe the properties of (uranium dioxide) nuclear fuel with additives. This report summarizes openly published information from tests and experiments, and mathematical theories that have been draw from the tests. The review has included fuel behaviour in normal operation and in transients as well as impact of irradiation. The report also discusses which data that are available and where information is missing.
Furthermore, mathematical models that can be used to analyse the behaviour and their physical explanations are described. Models and their description in this report are a starting point for possible implementation in computational programs such as the version of FRAPTRAN developed by Quantum Technologies AB.

Relevance

The relevance for SSM lies in gaining in-depth knowledge about nuclear fuel with additives: how these substances affect the properties of nuclear fuel, how the new variants have been tested and how they are modeled in different analysis programs.

Need for further research

The development of nuclear fuel is continuing with more variants and additives. Hence, there is a need to understand the behaviour of the new products in all situations that they can be exposed to during their operation and the margins that are necessary to impose for accident conditions. Tests will continue, for example in the research program SCIP-IV. At regular intervals, it is appropriate with a thorough and critical review of all that is done, like this one.