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The analysis of the DOUBLON experiment has provided C/E’s for several isotopic ratios in the first and second rows of the radial blanket after an irradiation in the PHENIX Sodium Fast Reactor. We have used this as a basis for the validation of the DARWIN-2.3 (Tsilanizara et al., 2000) package for the depletion calculation in the radial blankets of SFR’s (Lebrat et al., 2015). Unfortunately, no measurements have been performed in the upper and lower axial blankets of the fissile assemblies. Of course we expect our calculations to be reliable in these zones as well, as the initial compositions, nuclear reactions and neutron spectra are very similar. The representativity theory appeared to be the appropriate tool to correlate the available experimental information in the radial blanket to our calculations in the axial zones. Indeed, the representativity factors that we calculate between the final 239 Pu/ 238 U ratio in the radial and axial fertile zones are very close to 1. Hence, the measurements performed in the radial zone can help us “correct” the calculation in the axial blanket and reduce its a-priori uncertainty due to nuclear data. The estimated uncertainty reduction can reach a factor 5, since the experimental uncertainty is low. The 240 Pu/ 238 U ratio is studied with a similar method. [ABSTRACT FROM AUTHOR]

• DARWIN3-SFR aims to be the new reference at CEA for deterministic fuel depletion calculations. • We analyze measurements from the DOUBLON experiment in the fertile blanket of the PHENIX reactor. • The DARWIN3-SFR results are also compared to its predecessor DARWIN-2 and the reference stochastic code TRIPOLI-4. • The calculations reproduce well the average neutron flux and the production of most nuclides in the fertile blanket. • Important spatial discrepancies are observed and the production of 241Pu and 242Pu is not well reproduced. A reliable assessment of the final inventory in the fertile blanket of a Fast Neutron Reactor is an important issue for fuel cycle physics, as it impacts safety, reprocessing and design studies. The performances of fertile blankets neutronics calculations is a long standing issue, as there as specificities in these regions that are quite challenging, especially for depletion codes. The new CEA fuel depletion calculation package is DARWIN3-SFR, which incorporates the deterministic neutronics code APOLLO3® and the depletion module MENDEL. This paper details the validation of DARWIN3-SFR for fertile blanket calculations through the re-interpretation of the DOUBLON pin-irradiation in the Phenix reactor. During this irradiation, nine pins are studied through isotopic ratios, which give us information about the depletion and, indirectly, the neutron flux calculations inside the blanket. This environment is especially challenging for neutronics codes, since there is a strong variation of the neutron energy and population over a short distance. Our recent analysis of TRAPU - which is a similar experiment, but in the core center - has proven DARWIN3-SFR to be reliable for the fuel depletion calculations of fissile subassemblies; nevertheless, its performances in the fertile blankets still require validation. We observe that, once the calculated neutron flux level has been adjusted to the experiment through the 148Nd/238U ratio, DARWIN3-SFR provides results similar to the reference stochastic code TRIPOLI-4®. However, both codes have difficulties to reproduce some of the measured isotopic ratios inside the fertile blanket. Whilst DARWIN3-SFR produces identical results for most of the isotopes analysed (234U, 235U, 236U, 238Pu, 239Pu, 240Pu), variations of the neutron spectrum lead to some disparities for the production of 241Pu and 242Pu. Indeed, the low-energy flux estimation is higher with TRIPOLI-4® than with DARWIN3-SFR in the energy range where the 240Pu has a high capture cross section, which increases the calculated production of 241Pu and 242Pu. DARWIN3-SFR and its predecessor DARWIN-2 are efficient at calculating the average neutron flux level over the entire fertile blanket. However, the results of the two codes show a strong pin-to-pin dispersion, resulting in a different shape of the neutron flux inside the blanket. With DARWIN3-SFR, the estimated neutron spectrum is softer than in DARWIN-2, which impacts the 238U capture and fission reaction rates and hence the production of plutonium. [ABSTRACT FROM AUTHOR]

[Display omitted] • Decay heat measurements are indirect, difficult and rare. • Discrepancies between calculations and measurements are large in French SFR. • Previous comparisons between calculations and experiments are disparate. • Corrections were applied to the previous interpretation of a decay heat measurement in Phénix. Fast neutron reactors are of particular interest in the context of reducing carbon emissions, as they offer an attractive uranium economy and are crucial for closing the fuel cycle. To construct new reactors, safety issues must be studied thoroughly, and decay heat is a critical parameter, as demonstrated during the Fukushima accident. To ensure reactor safety, it is necessary to know the decay heat throughout the fuel cycle. Calculation tools are being developed at CEA and have been validated by comparing them with experiments performed in Sodium Fast Reactors Phénix and Superphénix. For many years, there have been inconsistencies between the experimental and calculated decay heat values for French SFRs. The analysis of the 2008 PUIREX experiment in Phénix has been revisited, and a new method has been tested to obtain the decay heat from temperature measurements. Explanations for the discrepancies with the calculations have been found. [ABSTRACT FROM AUTHOR]

• DARWIN-3 aims to be the new reference at CEA for deterministic fuel depletion calculations. • A comparison is made with results from the TRAPU irradiation experiment in the PHENIX reactor. • The DARWIN-3 results are also compared to its predecessor DARWIN-2 and the reference stochastic code TRIPOLI-4. • The production of U and Pu is in good agreement between DARWIN-2, DARWIN-3 and TRIPOLI-4®. • The discrepancies observed for some Am and Cm isotopes are explained by the slightly softer neutron energy spectrum calculated by DARWIN-3. The knowledge of the final inventory in the core of a Fast Reactor is required for many purposes, such as safety issues, reprocessing concerns or conception of new reactors. DARWIN-3 is the CEA code that aims to be the new reference for deterministic fuel depletion calculations. Composed of the deterministic neutronic code APOLLO3® and the depletion module MENDEL, it therefore needs to be validated by comparisons to experimental results or other fuel depletion codes. In this paper, the DARWIN-3 package performances are challenged for the validation of final inventory calculations in the core of a sodium-cooled fast reactor (SFR). This is done by reinterpreting the TRAPU experiment, which is a pin irradiation experiment that took place in the center of the PHENIX reactor between 1977 and 1979. During the TRAPU experiment, ten well-characterized fuel pins – of three different enrichment and Pu isotopic vectors – were placed in a subassembly near the center of the PHENIX core. At the end of the irradiation, the final amount of some isotopes results mainly from their initial concentration (e.g. plutonium, 241Am), whereas others – such as curium or 237Np – are produced exclusively during the irradiation; the final amount of these will be much more sensitive to potential modeling or calculation biases. We have computed Calculation/Experiment (C/E) ratios for different isotopic ratios at the end of the irradiation. A flux adjustment was performed in the calculations, in order to match the calculated 148Nd production to the experiment and avoid propagating a bias in the neutron flux calculation. The uncertainties take into account the experimental uncertainty, the statistical dispersion of the TRIPOLI-4® results and the statistical spread of the different sample results. For each calculated isotopic ratio, we have also assessed the associated uncertainty induced by the uncertainties on the nuclear data involved in the calculation. Comparisons with the previous deterministic package, DARWIN-2, composed of the ERANOS2 neutronic code and the PEPIN2 depletion module, as well as with the TRIPOLI-4® stochastic reference code, are performed. It appears that the production of uranium and plutonium are in agreement between DARWIN-3 and TRIPOLI-4®; the discrepancies observed for some americium and curium isotopes are explained by the slightly softer neutron energy spectrum in DARWIN-3 compared to TRIPOLI-4®. The disparities observed between DARWIN-2 and DARWIN-3 are also attributed to a difference in the neutron energy distribution calculated by the associated neutronic codes. This affects the calculation of the production of americium and curium, which are produced by reactions with large cross section resonances at low energy, where a small difference in the energy spectrum can result in a large difference on the reaction rate. The C/E for the production of those isotopes is worse with DARWIN-3 than it was with DARWIN-2; nevertheless, the production of neptunium, uranium and plutonium is compatible with both calculation codes. Due to its flexibility and attractive calculation time, DARWIN-3 allowed us to test some modeling hypothesis concerning the concentrations to be depleted, the type of decay chain, the effect of the nuclear data library and fuel temperature. [ABSTRACT FROM AUTHOR]