On-the-fly Temperature Treatment Routine for Unresolved Resonance Probability Table Sampling in Serpent 2

The Serpent Monte Carlo code is commonly used for reactor physics calculations, including multi-physics simulations, in which the neutronics solution is coupled to heat transfer and coolant flow. Since material temperatures in these applications depend on the operating state, also the physics model used in the Monte Carlo simulation has to be able to adapt to the changing conditions. Serpent applies the Target Motion Sampling (TMS) method to adjust the temperature of free-atom continuous-energy cross sections, and tabular interpolation for thermal scattering data. The previous methods, however, do not account for the unresolved resonance range, where cross sections are obtained by probability table sampling. This paper presents an extension of the on-the-fly temperature treatment capability to unresolved resonance probability tables. The method is based on tabular interpolation between two bracketing temperatures, and implemented in Serpent version 2.2.2. The implementation is demonstrated by test calculations.