Deterministic analysis of the Encapsulated Nuclear Heat Source by the European transport code ERANOS

A complete neutronic characterization of the Encapsulated Nuclear Heat Source (ENHS), a 125 MWth Lead-Bismuth cooled fast reactor, has been carried out by means of the European deterministic transport code ERANOS, in order to provide a complementary analysis of the system (including flux behavior, reactivity trend, mass balances, power distribution and more) with respect to the neutronic design already performed by MCNP. A preliminary sensitivity analysis has been performed to detect the optimal p/d ratio (1.34) and initial Pu enrichment (11.89 wt.%) which guarantee a keff nearly constant during the whole core lifetime of about 21 EFPY. Effects of both parameters on the reactivity value at BoL and its successive swing have been analyzed, discussed and quantified by the introduction of useful coefficients. Further investigations on the reactivity trend have been accomplished in case of thermal expansion of the system and, according to the evolution of the fuel with burnup, recomputing at each step the microscopic cross sections, in order to take into account any spectral effect.