Neutronic optimization of PHWR fuel

The PHWR fuel element optimization in argentine NPPs is considered from a neutronic perspective. The requirements related to the use of slightly enriched uranium in reactors originally designed to operate in the natural uranium fuel cycle, with increased exit burnups and increased residence time in the core, are better faced with thinner rods in a rod-dense bundle. A 52 rod bundle, currently under development, is analized and an improvement of a 48 rod bundle is proposed. Cell and complete core calculations are performed in order to establish the achievable exit burnup and to determine how far the fuel management strategy used in the natural uranium case has to be modified in order to satisfy the restrictions imposed by the thermalhydraulic limits in Atucha I reactor. The improvement in the void coefficient, which is always an important topic in these reactors, is examined in order to show that all the fuel elements considered give place to a negative void coefficient with an adequate combination of enrichment and absorbers in the bundle.