[en] This paper present basic nuclear reactor physics that may help to understand next challenges that nuclear industry have to face in the future. The ones considered in this work are waste production and natural resources consumption. This paper shows that waste and resources are linked by the plutonium status that could be considered as the principal waste or a valuable material that should be saved for a future transition to breeder reactors that could be for instance Sodium-cooled Fast Reactors (SFRs). This kind of reactors does not rely on natural resource supply, as it produces its own fissile material, plutonium-239, after a neutron capture on uranium-238. However, the operation of SFRs needs a huge amount of plutonium that should be produced in current Pressurized Water Reactors (PWRs). Natural uranium available on earth is expected to allow the operation of the global current fleet until approximately 2100 without major issues. The transition from PWRs to SFRs is then needed if and only if the nuclear industry will face an increase at a global scale during this century. If not, plutonium, the most radio-toxic element produced in PWRs, should be considered as a waste. Consequently, the plutonium status depends on the future evolution of nuclear energy. This paper shows that a status-quo means that plutonium should be considered as the most problematic element that should be handled on a long-term basis. On the other hand, a strong increase in nuclear energy on a global scale would imply that plutonium is a valuable material that would make a transition to SFRs possible. The first part of this paper describes basic nuclear physics that help up to understand nuclear reactor physics. It shows that a nuclear power plant design is a compromise between fuel enrichment costs and reactor costs, and explains why thermal reactors can operate with fuel enrichment to a few percents, whereas fast reactors must work with fuel with higher enrichment. The second part focuses on nuclear waste, their definitions, and characterizations. Finally, the last part is dedicated to natural resources consumption. It explains how plutonium can be used in new-generation reactors and presents the conditions for those reactors to be competitive. They are several possibilities for next-generation reactors; however, this paper focuses on the technology that is the most studied in Europe so far: sodium-cooled fast reactors (SFR)

[en] Highlights: • New flexible model for a wide range of Sodium cooled Fast Reactors inside CLASS. • Simplifications options lead to bias lower than 1% on actinides composition. • Precision of the meta-model better than 4% on major actinides in spent fuel. • Breeding ratios of designs covered go from 0.88 (burner) to 1.41 (breeder). • Biggest impact on breeding from blankets, major impact from isotopic composition. - Abstract: Since Sodium cooled Fast Reactors are present in many scenarios and strategies for the future of nuclear energy while not having a specific design established yet, we created a new fast and flexible model for the dynamic fuel cycle simulation tools CLASS. It includes a depletion meta-model and a fuel loading method based on artificial neural networks. It is able to represent a wide range of Sodium cooled Fast Reactor designs using oxide fuels and a wide range of fuel management strategies within fuel cycle simulation tools. A comprehensive analysis of simplification options has been made in order to choose the right level of complexity for the reference full core depletion calculations performed with the MURE code used for the training of the meta-model. The process from these reference calculations to the final meta-model is explained and a specific focus is given to the operations going from detailed full core depletion results to global results suitable for neural networks training. Details on the creation process for neural networks based predictors, one for each average cross-section, and their training on full core depletion calculations are given as well as the implementation within the CLASS code. The irradiation meta-model achieves good precision on all major and minor actinides present in spent fuel. The designs and loaded fuel covered by the model allow significant burner to strong breeder strategies. A sensitivity analysis shows that the number of fertile blankets is the primary contributor for breeding capabilities, but effects of isotopic composition are also significant. A test scenario illustrates the model capacity to simulate burner and breeder designs.

[en] β-decay properties are usually determined by measuring, with high resolution Ge crystals, the intensity and energy of γ-rays emitted after the beta decay. In the case of large Q_β, or complex de-excitation pattern, it happens that some transitions are missed due to the low efficiency of Germanium detectors for high energy gammas or high multiplicity decay cascades. This leads to an overestimation of the high energy part of the β spectra and the anti-neutrino ones. This is called the Pandemonium effect. Some of the data present in nuclear databases suffer from the distortion caused by this effect. A way to avoid the Pandemonium effect is to use a Total Absorption Spectrometer (TAS), this detector is a 4π calorimeter constituted of one large or segmented crystals and with the particularity of having a cascade detection efficiency close to 100%. A TAS device has been built and calibrated with "1"3"7Cs, "6"0Co and "2"2"-"2"4Na sources. A test performed on "9"2Rb shows that we have a good agreement between the simulated spectrum and the experimental one. The use of TAS for β-decay properties will help to assess the decay heat (or residual power) of reactors

[en] To study the β-decay properties of some well known delayed neutron emitters an experiment was performed in 2009 at the IGISOL facility (University of Jyvaeskylae in Finland) using Total Absorption γ-ray Spectroscopy (TAGS) technique. The aim of these measurements is to obtain the full β-strength distribution below the neutron separation energy (S_n) and above the γ/neutron competition. This piece of information is a key parameter in nuclear technology applications as well as in nuclear astrophysics and nuclear structure. Preliminary results of the analysis show a significant γ-branching ratio above S_n and this surprising result is in contradiction with the general assumption of neutron emission domination above S_n

[en] Three observables of interest for present and future reactors depend on the beta decay properties of the fission products: antineutrinos from reactors, the reactor decay heat and delayed neutron emission. In these proceedings, we present new results from summation calculations of the first two quantities quoted above, performed with evolved independent yields coupled with fission product decay data, from various nuclear data bases or models. New Total Absorption Gamma-ray Spectroscopy (TAGS) results from the latest experiment of the TAGS collaboration at the JYFL facility of Jyvaeskylae will be displayed as well as their impact on the antineutrino spectra and the decay heat associated to fission pulses of the main actinides. (authors)

[en] "9"2","9"3Rb are 2 fission products of importance in reactor antineutrino spectra and decay heat, but their β-decay properties are not well known. New measurements of "9"2","9"3Rb β-decay properties have been performed at the IGISOL facility (Jyvaeskylae, Finland) using Total Absorption Spectroscopy - TAS. TAS is complementary to techniques based on Germanium detectors. It implies the use of a calorimeter to measure the total gamma intensity de-exciting each level in the daughter nucleus providing a direct measurement of the beta feeding. In these proceedings we present preliminary results for "9"3Rb, our measured beta feedings for "9"2Rb and we show the impact of these results on reactor antineutrino spectra and decay heat calculations. (authors)