Interests of the improved quasi-static method for multi-physics calculations illustrated on a neutronics-thermomechanics coupling

The quasi-static method is widely used for space- and time-dependent neutron transport problems. It is based on the factorization of the flux into the product of two functions, an "amplitude" depending only on time and a "shape" which depends on all variables. Thanks to this factorization, long time-steps can be used for the computation of the shape, leading to a substantial reduction of the calculation time. Two algorithms, based on the quasi-static factorization, can be found in the literature: the "Improved Quasi-static Method" (IQM), and the "Predictor-Corrector Quasi-static Method" (PCQM). In this paper we show, on the example of the Godiva experiment, that the IQM algorithm can be easily adapted to multi-physics simulations. Moreover, most of the common coupling or time-step control strategies are compatible with this algorithm and we test some of them here. In particular, a technique taken from existing codes with point-kinetic modules and based on feedback coefficients is found to be especially efficient and gives precise and fast results. This shows that the multi-physics IQM presented in this paper is compatible with these existing codes, and is a way to couple them with neutron transport solvers.