Modelling of Liquid Injection Shutdown System (LISS) in ACR-1000

Abstract

The physics modelling of the Liquid Injection Shutdown System (Shutdown System 2, SDS-2) accounts for the major phenomena that occur in the ACR-1000 reactor core following the activation of that system, by combining the effects of two major components: the moderator hydraulics and the neutronics. The moderator hydraulics must provide realistic modelling of the poison volumes and of the time of entry of the poison fluid into the reactor, as well as propagation of the poison into the moderator after emission from the nozzle. The neutronics must provide a realistic evaluation of the reactivity worth of varying volumes and geometries of poisoned moderator fluid for a range of poison concentrations, in order to simulate the reactivity effect of the injected poison. The time dependent poison is generated from hydraulic calculations and the neutronics data are generated for a number of standard geometries and concentrations using the supercell code DRAGON [1]. The neutronics calculation must simulate the variety of geometries that ensue from the poison injection, i.e., the poison inside the nozzle before emission, and poison jets exiting the pipe at two orientations; horizontally and at 60 degrees to the horizontal. The methodology for the reactor physics simulation of SDS-2 for the ACR-1000 will be presented in this paper.