Nuclear Data Needs for the Assessment of Generation IV Nuclear Energy Systems G. Rimpault

1. Nuclear Data Needs for the Assessment of Generation IV Nuclear Energy Systems G. Rimpault Commissariat à l’Energie Atomique (CEA) Cadarache Center 13108 Saint-Paul-lez-Durance Cedex, France grimpault@cea.fr CEA/DER Cadarache Centre Gérald Rimpault

2. Summary The current presentation is aiming at describing the methodology for defining nuclear data needs and the short list of high priority ones. Items covered • Target accuracies for GEN-IV neutronic characteristics • The covariance data • The integral uncertainties due to nuclear data • Uncertainties Requested for Nuclear Data • Integral Experiments: A way to Assess Nuclear Data • Experimental Data Base • Conclusion and Perspectives CEA/DER Cadarache Centre Gérald Rimpault

3. Target accuracies for GEN-IV neutronic characteristics The design of the cores and fuel cycles of the Gen IV systems relies on some neutronic characteristics. Target accuracies are requested at the different stages of the design studies (1st stage: viability; 2nd stage: performance). CEA/DER Cadarache Centre Gérald Rimpault

4. Target accuracies for GEN-IV neutronic characteristics Target accuracies requested for the performance stage of the design studies are indicative and are under improvement in: Na-cooled FR with CRP on AIEA on « updated codes and methods to reduce the calculational uncertainties of the LMFR reactivity effects » with: • Phase 4 : Check the safe behaviour of the BN600 core fully loaded with MOX using weapon grade Plutonium (already performed) • Phase 6 : Check the safe behaviour of the BN600 core fully loaded with MOX from Thermal Reactor spent fuel cooled down 50 years (in progress) Objective: Check the Safety Behaviors with increase MA content up to 6% and associated method and nuclear data uncertainties CEA/DER Cadarache Centre Gérald Rimpault

5. Results for BN600 Phases 4 and 6 variants with JEF2.2 Large difference on K-eff between Phase 4 and Phase 6 Doppler constant reduced by a factor 2 Sodium density coefficient significantly increased CEA/DER Cadarache Centre Gérald Rimpault

6. Results for BN600 Phases 4 and 6 variants with JEFF3.1 No more difference on K-eff between Phase 4 and Phase 6 Doppler constant reduced by a factor 2 Sodium density coefficient significantly increased CEA/DER Cadarache Centre Gérald Rimpault

7. Differences between JEFF-3.1 and JEF-2.2 No difference on K-eff between JEFF-3.1 and JEF-2.2 on Phase 4 Large difference on K-eff between JEFF-3.1 and JEF-2.2 on Phase 6 Doppler constant remains insensitive to nuclear data libraries Sodium density coefficient increased uniformally CEA/DER Cadarache Centre Gérald Rimpault

8. Target accuracies for GEN-IV neutronic characteristics Target accuracies requested for the performance stage of the design studies are indicative and are under improvement in: He-cooled FR with EU GCFR core physics group CRP with objectives: • Assessing the method uncertainties • Defining the nuclear data uncertainties on reactivity coefficients (includes EOC composition changes) Objective: Check the safe behavior of the GCFR 2400MWth CERCER with associated method and nuclear data uncertainties (in progress) CEA/DER Cadarache Centre Gérald Rimpault

9. Base data sensitivity and integral uncertainty In order to get uncertainty on integral characteristics of the core sensitivities and variance covariance matrices are needed. Works already performed by • G. Aliberti et al. “Nuclear Data Sensitivity, Uncertainty and Target Accuracy Assessment for Future Nuclear Systems” and • S. Ohki “Target accuracy of MA nuclear data” can be considered as a basis for current task. Further work, however is still required for: • The anisotropy of scattering • The impact of burn up xs on reactivity coefficients and other characteristics (this includes the FP xs) This work is planned at CEA with a PhD student CEA/DER Cadarache Centre Gérald Rimpault

10. Variance-covariance matrix B associated to nuclear data The variance-covariance matrix B associated to nuclear data should be associated to nuclear data evaluation and this is the first request for evaluators since values at the moment are scarce. However, in order to make progress on the design request lines, simple variance- covariance matrices have been estimated for a few nuclides More fundamental work is in progress at CEA/Cadarache at the evaluation level (see next viewgraph) However, caution should exist if integral measurements are taken as a source of information for setting an evaluation. Users should be aware of it, not to double count the information in their assessment studies CEA/DER Cadarache Centre Gérald Rimpault

11. Nuclear data file developments – Future work Uncertainties and covariance data Thermal and epithermal energy range produced with SAMMY or CONRAD Produced with TALYS* « Full  correlation matrix »   0.01 meV 10 keV 0.01 meV 10 keV 10 MeV 20 MeV 0.01 meV 10 keV 10 MeV 20 MeV CEA/DER Cadarache Centre Gérald Rimpault

12. Integral Uncertainties due to current Nuclear Data Clean core measurements (critical mass, buckling, K-infinity, spectral indices) performed in MASURCA, ZEBRA and SNEAK facilities for fast systems but also EOLE and MINERVE facilities for thermal systems are used to assess the performance of nuclear data libraries. There are also post irradiation experiments which provide more information on capture xs The results obtained are associated with large uncertainties due to current nuclear data libraries and hide the existence of compensating errors CEA/DER Cadarache Centre Gérald Rimpault

13. Adjusted Nuclear Data Libraries In the past getting the required target accuracies was achieved through adjustment of nuclear data on integral measurements. Recent differential measurements give evidence of the validity of such an approach while others show difficulties in achieving the desired goal Convergence on Nuclear Data between values deduced from the adjustment and recent differential measurement is observed. Most spectacular examples are illustrated by: • Na cross sections • Pu240 cross sections CEA/DER Cadarache Centre Gérald Rimpault

14. Sodium Inelastic Cross Sections: Adjusted and Evaluated Na Measurements Performed at Geel Resonance structure coherent with total cross section measured at ORNL CEA/DER Cadarache Centre Gérald Rimpault

15. Uncertainties on SFR Critical Masses due to the Nuclear Data Predictability of Critical Masses • the obtained adjusted ERALIB1 uncertainties are consistent with the target accuracy required for sodium-cooled oxide fast reactors CEA/DER Cadarache Centre Gérald Rimpault

16. Uncertainties on SFR Power Map due to the Nuclear Data Predictability of Power Map Distribution • the obtained adjusted dERALIB1 uncertainties are consistent with the target accuracy required for sodium-cooled oxide fast reactors CEA/DER Cadarache Centre Gérald Rimpault

17. Uncertainties Requested for Nuclear Data The uncertainties on nuclear data as they have been obtained with ERALIB1 fulfil the SFR and GFR design requests for those major nuclides of interest Pu239, Pu240, Pu241, U238, U235 , Fe, Cr, Ni, Na, O. It is therefore worth looking at the standard deviations before and after adjustment to find out where new differential measurements are needed The approach is approximate since correlations within ERALIB1 offer a way to significantly reduce the impact of standard deviations. And there are still pending problems associated to some ERALIB1 nuclides such as the one on structural materials (Fe, Cr, Ni) which need to be considered and might be due to adjustment approximation CEA/DER Cadarache Centre Gérald Rimpault

18. Integral Experiments: A Way to Assess Nuclear Data Integral Experiments can be used as an evidence of insufficiency in existing evaluations. Cautious should be given to potential bias which exist in integral experiment as it exists in differential measurements. Integral Experiments have a complementary role to differential measurements for meeting some nuclear data needs (for instance Pu239 fission). Standard deviations need to account for the uncertainties due to integral measurements as well as differential measurements. This way to proceed offers a way to better evaluations which might be usable in Monte Carlo codes as in deterministic ones. CEA/DER Cadarache Centre Gérald Rimpault

19. Experimental Base for Actinides Nuclear Data Validation Thermal spectrum Fast Spectrum MASURCA Keff, indices COSMO BFS 67,69,71 OSMOSE Critical Experiments XS & Branching Ratios SUPER PROFIL PROFIL 1&2 UOX (3.1%, 4.5%) JOYO SUPERFACT PROFIL M MOX TRAPU Post Irradiation Experiments CEA/DER Cadarache Centre Gérald Rimpault

20. Experimental Base for FP Nuclear Data Validation Thermal spectrum Fast Spectrum STEK oscillations DIMPLE SEG oscillations MINERVE Critical Experiments XS & Branching Ratios SUPER PROFIL PROFIL 1&2 Post Irradiation Experiments PROFIL- M CEA/DER Cadarache Centre Gérald Rimpault

21. Conclusion and Perspectives The methodology for defining nuclear data needs has been briefly covered. Target accuracies for GEN-IV neutronic characteristics is an important point to start with The covariance data is of significant importance for quantifying the needs and evaluators should provide them with their nuclear data. Nuclear Data Requests should be associated to uncertainty values. Integral Experiments have a complementary role to differential measurements for meeting some nuclear data needs (for instance Pu239 fission). A list of potential requests is existing, quantifying their uncertainties remain a significant effort particularly when looking at fuel cycle quantities. CEA/DER Cadarache Centre Gérald Rimpault