Preliminary analysis of startup transient for an ultra-small lithium-cooled space reactor power system

Abstract

A multi-phases startup scheme based on the reactor startup first, followed by the closed Brayton cycle (CBC) machinery was proposed for the startup condition of an ultra-small lithium-cooled space reactor power system (ULCR) with a CBC conversion system concept scheme. The scheme minimizes the auxiliary motor power required for the turbomachinery startup. The overall startup process includes 7 phases. In the low-power operation phase, by controlling the turbomachinery shaft speed and helium-xenon (He–Xe) working fluid mass flow, the turbomachinery output power was balanced with the needed motor power. Therefore, the auxiliary equipment of the power conversion system was minimized. As the turbomachinery speed and He–Xe mass flow increased to the rated conditions, the core was in low temperature and low power steady-state operation, which was conducive to keep system in safety conditions for the automatic control system. With the reactivity insertion, the core temperature was finally increased to the rated operating condition, and the CBC conversion system's output power increased to the rated output power. The transient process of the designed startup scheme was calculated and analyzed by using the developed transient analysis program TACSNR. The results show that the change rate of the core average temperature at the rising phases was less than 1.1 K s−1. During the whole startup process, the parameters of the ULCR system are all in the safe range.