Dynamic Heat Transfer Characteristics of a Nuclear Rocket Reactor

The nuclear rocket engine is required to start or change power levels in very short times. This requires that limitations on fast transients be well known and the transient flow and power schedules designed to avoid these limitations. At the same time it is desired that the schedules allow the least use of propellant at other than the maximum specific impulse. Limitations on reactor transients as a result of heat transfer phenomenon consist of thermal stresses, flow choking in the reflector or core cooling passages, laminar flow instability, and two phase flow into the core resulting in unpredictable reactor power perturbations. Studies have been made showing the effect of power and flow schedules on the maximum fuel temperature and the propellant exit temperature. The model used for calculation consists of a single flow channel and its accompanying material for both the reflector and the core. Computations performed for increase and decrease in thrust show the effect of the power schedule leading or lagging the flow schedule. It is found that the power schedule should lead the flow schedule on an increase of thrust and lead it on a decrease of thrust if it is desired to hold a constant propellant exit temperature. If for some reason propellant flow to the reactor is instantaneously lost and the reactor is scrammed, it is shown that flow must be resumed in adequate amounts for cooling within 1 second or damage to the core will result.