Nuclear Reactors Fuel Cycle : from the Third Generation to the Fourth Generation

There are two main types of fuel management:

• the open cycle, where spent fuel is considered as final waste, destined for geological disposal;

• the closed cycle, in which the recoverable materials (uranium and plutonium) contained in spent fuel are recycled. The remaining material in the spent fuel is the final waste, which, after vitrification, is placed in geological disposal.

In France, the fuel cycle has not been completely open for almost 30 years. The recycling of plutonium in MOX fuel was first implemented in 1987 at the Saint-Laurent- des-Eaux power plant, and the recycling of reprocessed uranium in the form of ERU fuel was first implemented in 1994 at the Cruas power plant. In fact, the fuel cycle is constantly evolving with very long time constants, both in terms of the design of these developments and their effects once deployed. For example, the feasibility of plutonium recycling in PWRs was demonstrated by experiments that began as early as 1963 in the Belgian BR3 pressurized water reactor and continued in the Chooz A power plant from 1974. The decision to recycle it industrially in France was taken in 1985. Since deployment of the French PWR fleet began in the second half of the 1970s, numerous developments have been made to improve uranium utilization efficiency and optimize waste management: average burnup rates have risen from around 30 GWj/tU to 45 GWj/tU in the 2000s, thanks to the implementation of new fuel management systems, enriched uranium fuel unloaded from reactors has been processed since the early 1980s, and plutonium and reprocessed uranium have been recycled. All these developments have multiple impacts on materials and waste management, reactors and cycle facilities - in other words, on the "nuclear system", the coherence of which must be ensured over the long term. These impacts occur on different timescales, some of them very distant, and it is essential to anticipate them early enough.

Of course, further developments are still to come with the current fleet, and with the commissioning of 3rd generation reactors such as the EPR, where the cycle will remain partially closed. The complete closure of the cycle will come with 4th generation nuclear systems, which have been the focus of major developments worldwide since the early 2000s, whether as part of international collaboration through the Generation IV International Forum, or as part of national programs. In addition to the objectives of 3rd-generation reactors (safety, competitiveness), these systems are also designed to meet sustainability objectives: making better use of fuel resources and optimizing nuclear waste management. The 4th generation systems currently under study are mostly...