Introducing a new type of fuel in EDF reactors: Main issues. Introducing a New Fuel in EDF Reactors: Main Issues

The main issues associated with the introduction of a new fuel design at an industrial level in EDF reactors are the following: in-core operational feedback, coherence of the nuclear fuel cycle and mixed cores. In-core operational feedback Once all possible experimental results have been obtained for a new fuel design, in-core qualification is necessary to assess its robustness and reliability prior to an industrial use. That qualification involves several steps to gather the relevant operational feedback at minimum risk: - irradiation of a few LTA's during a number of operating cycles greater than what would be needed on an industrial scale, with specific exams and rod extractions at the end of each fuel cycle: that first step is 5 to 6 years long; - loading whole reloads with the new fuel design in a dedicated reactor is then requested if the new fuel design is associated with a new structure design; in that case, only a full core with the new design will enable checking the behaviour of that fuel with respect to GTRF and assembly bow: that second step may take another 5 to 6 years. Altogether, the whole in-core qualification process might need more than 10 years. Considering that 10 other years could be necessary to finalise a design for LTA's, the qualification on an industrial case could be targeted around 2032. By then, the average age of EDF existing reactors will be 47 years old. Coherence of the nuclear fuel cycle The feasibility of a new fuel design needs to be assessed for each step of the fuel cycle. The specificity in the French nuclear fuel cycle stems from the spent fuel processing performed at La Hague plant, and the recycling of the recovered recyclable materials (uranium and plutonium). When a new fuel is used at an industrial scale, it is necessary to keep the feasibility of plutonium and reprocessed uranium recycling safe, taking into account the reactors safety limitations. For example, the increase in the average fuel assembly discharge burn-up from about 33 GWd/t to about 45 GWd/t between 1990 and 2010 led to an increase in the share of even isotopes in recovered Pu and RepU, with reduced energetic equivalencies and radioprotection issues. Some adaptations have been or will be implemented in the nuclear fuel cycle to deal with that change in isotopic qualities. When we enter a new fuel design, it is necessary to justify its compatibility with co-resident fuels. That justification is all the more important and difficult because the new fuel design is significantly different. If the compatibility cannot be demonstrated, the ultimate solution would be to entirely discharge the core and reload it with the new design only, which would be very costly. Entering a new fuel design at an industrial scale in EDF reactors can be a very long process, and in the case of an ATF fuel, some additional time is necessary to finalise the LTA's design. However, depending on the remaining life duration of the reactors, it might be worth considering a breakthrough technology for PWRs, especially if significantly improved safety margins might be an incentive to consider life extension for the reactors