Acceleration of fission source convergence in the Serpent 2 Monte Carlo code using a response matrix based solution for the initial source distribution

This paper presents a new response matrix based solver implemented in the Serpent 2 Monte Carlo code for the purpose of producing an improved initial guess to accelerate source convergence in criticality source simulations. The solver obtains coupling coefficients required for the response matrix solution from Monte Carlo simulations, and provides a spatial distribution that approximates the converged fission source. The implemented methodology is demonstrated by single-assembly and full-core PWR calculations. The results show that the improved initial guess leads to faster source convergence in terms of both inactive cycles and overall running time.