The effect of core configuration on temperature coefficient of reactivity in IRR-1

Experiments designed to measure the effect of coolant moderator temperature on core reactivity in an HEU swimming pool type reactor were performed. The moderator temperature coefficient of reactivity (αω) was obtained and found to be different in two core loadings. The measured αω of one core loading was -13 pcm/degrees C at the temperature range of 23-30 degrees C. This value of αω is comparable to the data published by the IAEA. The αω measured in the second core loading was found to be -8 pcm/degrees C at the same temperature range. Another phenomenon considered in this study is core behavior during reactivity insertion transient. The results were compared to a core simulation using the Dynamic Simulator for Nuclear Power Plants. It was found that in the second core loading factors other than the moderator temperature influence the core reactivity more than expected. These effects proved to be extremely dependent on core configuration and may in certain core loadings render the reactor's reactivity coefficient undesirable