Advances in Reactor Core Fuel Management

The development of light water reactor (LWR) core fuel management over the last decades was mainly driven by economic considerations. One of the most efficient measures to improve LWR plant economics is the increase of reload fuel discharge burn-up. Depending on the different national licensing environments, back-end scenarios and utility requirements this target can be achieved by specific optimization of different quantities; i.e. fuel cycle strategy (cycle length), reload enrichment (235U enrichment), burnable absorber use (e.g. Gd2O3) and reload fuel type (e.g. UO2/PuO2 mixed oxide fuel). This paper presents an overview of recent and future steps towards high burn-up in European countries and the U.S., reflecting the different legal and economic boundary conditions. The evolution of reactivity feedback characteristics (moderator temperature, Doppler, void coefficient, boron worth) with advanced core designs and increasing burn-up is discussed using a specific PWR example including consequences for normal cycle operation. The importance of continuous validation of the core design tools with respect to increasing burn-up and higher core heterogeneity is emphasized followed by a brief discussion on the impact of high fuel burn-ups on core behaviour under accidental conditions (steam line break, RIA, ATWS). (author)