Dry critical experiments and analyses performed in support of the TOPAZ-2 safety program

In December 1991, the Strategic Defense Initiative Organization decided to investigate the possibility of launching a Russian Topaz‐2 space nuclear power system. Functional safety requirements developed for the Topaz mission mandated that the reactor remain subcritical when flooded and immersed in water. Initial experiments and analyses performed in Russia and the United States indicated that the reactor could potentially become supercritical in several water‐ or sand‐immersion scenarios. Consequently, a series of critical experiments was performed on the Narciss M‐II facility at the Kurchatov Institute to measure the reactivity effects of water and sand immersion, to quantify the effectiveness of reactor modifications proposed to preclude criticality, and to benchmark the calculational methods and nuclear data used in the Topaz‐2 safety analyses. In this paper we describe the Narciss M‐II experimental configurations along with the associated calculational models and methods. We also present and compare t...