Since 1991, the OECD Nuclear Energy Agency (NEA) has conducted a number of scientific studies to examine nuclear fuel burn-up issues as applied to criticality safety in the transportation, storage and treatment of spent fuel. They have covered a wide range of fuel types, including UOX and MOX fuels for PWR, BWR and VVER reactors.
The objective of the current study was to examine the axial burn-up profiles of PWR UO2 spent fuel assemblies and specifically the fuel assembly end effects and the axial fission density distributions. The study was based on the evaluation of a database of experimentally measured axial burn-up profiles of the Siemens Convoy fuel assemblies, irradiated in the German nuclear power plant Neckarwestheim II.
The report analyses and summarises the solutions to the specified benchmark exercises provided by ten contributors from seven countries. It shows that there is a significant correlation between the asymmetry of axial fuel assembly burn-up profiles and both the end effect and the axial fission density distribution. The results also illustrate the importance of using accurate axial fuel burn-up profiles when designing transport/storage fuel casks.