MCNPX and HELIOS-2 comparison for the neutronics calculations of a Supercritical Water Reactor HPLWR

The Supercritical Water Reactor (SCWR) is one of the most promising and innovative designs selected by the Generation IV International Forum. One of the concepts that is being studied is the High Performance Light Water Reactor (HPLWR) which is the European version of the SCWR. For this reactor, neutronics calculations have been performed with MCNP/MCNP5/MCNP4B/MCNPX4C and the results obtained are used as reference. However, MCNP calculations take too much computing time for design or fuel management analysis; therefore, it was decided to explore the factibility of using the HELIOS-2 code given that the computing time required for the simulations is notably reduced. The main objective of this work is to develop a model for the HPLWR fuel with HELIOS-2, and to subsequently compare the results against the MCNPX, in order to use the HELIOS-2 for performing further reactor physics studies given that although MCNPX is better HELIOS-2 is faster.Several variables, which are essential in the neutronics design of any reactor, were compared, that means: the infinite neutron multiplication factor (k∞), the pin power distribution, and the power peaking factor for the fuel assembly, in hot and cold conditions, as well as the fuel reactivity coefficients. Calculations were made for a square fuel assembly with two rows of fuel pins, some of them containing gadolinia (Gd2O3) as burnable absorber material. The tests were simulated for different gadolinia enrichments as well as for no gadolinia. The calculations were done with the total reflection condition. The results show good similarities between the deterministic HELIOS-2 and the stochastic MCNPX calculations for the selected fuel assembly. Almost all values of the maximum power peaking factor obtained from MCNPX and HELIOS-2 are very similar to each other. Regarding the k∞ values, the maximum relative difference (considering fuel temperature variations between 400 and 1200 K) is 564 pcm Δk/k for a coolant density of 0.74 g/cm3 and 1200 K.According to results, the HELIOS-2 code is good enough to be used in neutronics simulations of a HPLWR. In regards to reactivity coefficients, due to fuel temperature variations, we obtained similar results with both codes. We concluded that HELIOS-2 can be used for making HPLWR analysis faster than MCNPX.

► We modeled with HELIOS-2 and MCNPX fuel lattices of HPLWR that use supercritical water as coolant.
► Neutronics calculations were carried out for cold and hot conditions, and for different coolant densities.
► Neutronics calculations were made for lattices with and without gadolinia pins.
► We compared the k-infinite, the maximum PPF, the pin power distribution, and the fuel temperature reactivity coefficient.
► Results showed that HELIOS-2 is good enough to be used for the fuel lattice calculations of this reactor.