IMPLEMENTATION OF THE QUASI-STATIC METHOD FOR NEUTRON TRANSPORT

The study of the dynamic behavior of next generation nuclear reactors is a fundamental aspect for safety and reliability assessments. Despite the growing performances of modern computers, the full solution of the neutron Boltzmann equation in the time domain is still an impracticable task, thus several approximate dynamic models have been proposed for the simulation of nuclear reactor transients; the quasi-static method represents the standard tool currently adopted for the space-time solution of neutron transport problems. All the practical applications of this method that have been proposed contain a major limit, consisting in the use of isotropic quantities, such as scalar uxes and isotropic external neutron sources, being the only data structures available in most deterministic transport codes. The loss of the angular information produces both inaccuracies in the solution of the kinetic model and the inconsistency of the quasi-static method itself. The present paper is devoted to the implementation of a consistent quasi-static method. The computational platform developed by CEA in Cadarache has been used for the creation of a kinetic package to be coupled with the existing SNATCH solver, a discrete-ordinate multi-dimensional neutron transport solver, employed for the solution of the steady-state Boltzmann equation. The work aims at highlighting the eects of the angular treatment of the neutron ux on the transient analysis, comparing the results with those produced by the previous implementations of the quasi-static method. The innovative features introduced by next generation nuclear reactors require as much innovation in the analysis of their performances and safety aspects. The safety assessment of such reactors, in particular, requires the accurate simulation of the behavior of the reactor core during typical operational and accidental conditions, with the need for the solution of the neutron