Analysis of primary containment response with upper internal structure

Abstract

In the fast reactor containment the upper internal structure is a massive structural component located in the region above the core. The main body of this structure consists of four support columns, an upper plate and a lower plate holding numerous coolant passageways for directing the core sodium to the outlet plenum. The aim of this paper is to provide hydrodynamic analysis of the fluid motion in the above core region and to study the effect of the upper internal structure on the slug impact as well as the primary system response. At ANL, two excursion containment codes, ICECO and ALICE, are chosen for such an analysis. These two codes, based on the ICE technique and ICED-ALE method, respectively, are ideal for analyzing flow through coolant passageways and flow blockage near the bottom plate. They also have other advantages, such as: (1) treating fluid motion around internal structure with geometrical discontinuities; (2) investigating excursions with large distortions; (3) handling two-dimensional sliding conditions; and (4) providing a stable solution throughout the entire excursion. In both ICECO and ALICE the upper internal structure can be modelled by rigid obstacles similar to the scheme used in the MAC method. The coolant passageways can be approximated by means of narrow cells. Another option is provided in the ICECO code in which the upper internal is considered as a perforated structure. In this model large cells can be used over the entire computational region. The analysis utilizes a control-volume technique to solve the conservation equations of mass, momentum, and energy. The basic idea is to use the actual fluid volume and the actual flow area in the mathematical formulation. Three modified Poisson equations are derived which govern the hydrodynamic pressures inside, above, and below the perforated structure. These three equations, in conjunction with the Poisson equation of the ICE technique as well as the relaxation equation at the moving boundary, are solved iteratively. Two sample problems are given. The first one deals with the ICECO analysis of primary containment response to an HCDA. The effect of the upper internal structure on the wave propagation and slug impact are investigated. The second example presents a simulation of SRI complex vessel experiments using the Alice code. The results are discussed in detail.