Stakes and scientific challenges for a sustainable use of Uranium and Plutonium in the French nuclear fuel cycle
Résumé
The current French recycling strategy takes advantage of the 10 MT of plutonium produced annually
by the irradiation of the UOX fuel in the French LWR fleet. This recycling strategy aims at saving natural
uranium resources as well as decreasing the net production of plutonium, safely recovered and
recycled in the MOX fuels. It also limits the necessary interim storage and future final disposal
capacities and prevents any residual plutonium content in the high-level nuclear glass waste. Although
the feasibility of MOX reprocessing is already considered proven at an industrial scale, the used MOX
fuel (100-120 t/y), which still contains a fraction of potentially reusable plutonium, is currently
untreated and stored.
The French Energy Transition Act and the Multi-annual Energy Program (2019-2028) make several
commitments and notably:
I. net zero CO2 emissions by 2050,
II. Decreasing the share of nuclear energy in the electric mix down to 50% by 2035, and shutting
down 14 LWRs by 2035 consequently; recent presidential announcements are however in
favor of extending the lifetime of existing reactors and building soon new EPRs (6 initially with
a study of 8 more).
III. Increasing the amount of renewable energies in the mix consequently.
IV. Maintaining the recycling strategy at least until the years 2040.
The MOX fuel is currently used in the 900 MWe LWRs, which will be shut down first; partially “MOXing”
the 1300 MWe LWRs will compensate this.
In the long run (on the horizon of the end of the 21st century), the nuclear industry has to be prepared
for a potential forthcoming lack of natural uranium available at an economically viable cost. Therefore,
a sustainable closed fuel cycle strategy makes it necessary to introduce the 4th Generation fast neutron
reactors into the fleet, which are able to take the best benefit of every actinide isotopes through a
better neutron fission/absorption ratio. The option of using molten salt reactors to carry out the
transmutation of actinides is also under study, with specific scientific challenges at stake.
Meanwhile, French industry should pave the way for multi-recycling Pu and U in the current LWRs. The
option of multi-recycling plutonium in LWRs implies an increase in the plutonium flux and a
degradationof the plutonium isotopic composition, which induces several hurdles concerning the
safety, radiation protection and operating conditions of the reactors and the fuel cycle (reprocessing
and fabrication). In particular, concerning the fuel cycle, a dedicated R&D program addresses
innovative options for reprocessing (dissolution of more refractory oxide pellets, simplified separation process). In this talk, we address the main scientific challenges associated with this step-by-step
strategy towards a sustainable Pu « full recycling » and highlight the need for improvements and
simplifications in the MOX fuel reprocessing and manufacturing operations required by the notably
increasing quantity of degraded plutonium in the fuel cycle.