Prediction of the energy per fission and heating in advanced gas-cooled reactors

Lattice codes often approximate the energy release per fission as a nuclide-dependent constant. In recent years the effect of this approximation has been examined, and some lattice codes have moved to a more accurate determination of this fundamental parameter. In this work we calculate the energy per fission and the distribution of fission energy deposition in the lattice cell of an advanced gas-cooled reactor (AGR), using coupled neutron, photon calculations with WIMS10 and MCNP6. We also compare these results to an energy per fission estimated using a simple model. We replicate previous results by showing that the component due to neutron capture has significant enrichment and burnup dependence, which is not represented by the typical approximation to the energy per fission, and show that this could affect the calculation of assembly power by up to a few percent. The AGRs which EDF Energy operate are unusual in allowing a thermal calculation of the power generated by each fuel assembly, independent of the neutronic calculation. These calculations are based on temperature measurements and in principle provide a means of validating the prediction of the energy per fission. We show that observed discrepancies between thermal and neutronic power predictions could be reduced by using more accurate values of the energy release per fission. (author)