Design of a Guaranteed Shutdown State Using Solid Rods for the ACR-1000 Reactor

Abstract

The design of a rod-based system for the guaranteed shutdown state (GSS) of the ACR-1000 reactor is presented. Previous CANDU designs rely on soluble neutron poisons to achieve long-term shutdown. The GSS design presented here uses solid boron carbide rods with a simple drive system, thus reducing the operational overhead of using soluable poison. A subcriticality design target of -50 mk was chosen in accordance with IAEA guidelines for long-term fuel storage. An additional -5 mk was added to the target to account for code uncertainties. The most valuable rod was eliminated from the analysis to address the possible unavailability of a device. Also, the sub-criticality calculations assume that the core is cold and that the short-lived fission products have decayed, each of which results in additional positive reactivity in the core. RFSP was used as a preliminary tool to determine the device locations and the most valuable reactivity devices. The resulting configurations were subsequently simulated with the code MCNP5, to determine if the design complied with the subcriticality criteria.