Dynamics of Clustered Nuclear Engines

A short review is presented of investigations concerning clustering of multiple identical solid core nuclear engines in a polygon arrangment, for space propulsion. A unique aspect of nuclear engine clustering is the coupling between reactors due to the exchange of neutrons which propagate transients within the system. A method has been developed at Douglas for evaluating the reactivity coupling effect for various reactor types and cluster arrangements. The results are in good agreement with available experimental data. An analog model of a clustered nuclear propulsion system has been used for simulating the operating cycle, with emphasis on the inherent control offered by the presence of hydrogen in the reactor. Coupling effects during transients, including start-up, abnormal reactivity perturbations, and an engine-out event are the major points of interest.