Needs of accurate prompt and delayed $\gamma$-spectrum and multiplicity for Nuclear Reactor Designs

International audienceThe local energy photon deposit must be accounted accurately for Gen-IV fast reactors, advanced light-water nuclear reactors (Gen-III$^+$) and the new experimental Jules Horowitz Reactor (JHR). The energy accounts for about 10 percent of the total energy released in the core of a thermal or fast reactor. The $\gamma$-energy release is much greater in the core of the reactor than in its structural sub-assemblies (such as reflector, control rod followers, dummy sub-assemblies). However, because of the propagation of $\gamma$ from the core regions to the neighboring fuel-free assemblies, the contribution of $\gamma$ energy to the total heating can be dominant. For reasons related to their performance, power reactors require a 7.5 percent (1$\sigma$) uncertainty for the energy deposition in non-fuelled zones. For the JHR material-testing reactor, a 5 percent (1s) uncertainty is required in experimental positions. In order to verify the adequacy of the calculation of $\gamma$-heating, TLD and $\gamma$-fission chambers were used to derive the experimental heating values. Experimental programs were and are still conducted in different Cadarache facilities such as MASURCA (for SFR), MINERVE and EOLE (for JHR and Gen-III$^+$ reactors). The comparison of calculated and measured $\gamma$-heating values shows an underestimation in all experimental programs indicating that for the most $\gamma$-production data from $^{239}$Pu in current nuclear-data libraries is highly suspicious. The first evaluation priority is for prompt-multiplicity for $^{235}$U and $^{239}$Pu fission but similar values for other actinides such as$^{241}$Pu and $^{238}$U are also required. The nuclear data library JEFF3.1.1 contains most of the photon production data. However, there are some nuclei for which there are missing or erroneous data which need to be completed or modified. A review of the data available shows a lack of measurements for conducting serious evaluation efforts. New measurements are needed to guide new evaluation efforts which benefit from consolidated modeling techniques