Anomalous peculiarity of coolant temperature feedback in PWRs

According to conventional thinking on power regulation in a reactor with a negative feedback, the power change has the same sign as the introduced reactivity causing it. In this study we consider the opposite situation, which is anomalous in the sense of the usual power behavior. This anomaly connects with spatial peculiarity of coolant temperature reactivity effect and predisposition to it is inherited for reactors, which are sufficiently large in the direction of the coolant flow. The analysis is performed using simplified one-dimensional reactor models with one feedback on the coolant temperature. In the perpendicular (radial) direction reactor is assumed to be uniform and infinite. Some PWR cores are considered with respect to this anomaly. It is shown the anomaly could occur in PWR with no other feedbacks.