Realizing out-core reactivity control with control drums: application of burnable poisons in microreactor

Abstract

Microreactors are distinguished by their compact configuration, cost-effectiveness, and adaptable deployment, which has prompted extensive research attention worldwide. In the realm of reactivity control methodologies, the utilization of drums has been identified as a more efficacious approach when it comes to the compactness of microreactors. The employment of burnable poisons in microreactors has been demonstrated to be an effective strategy for reducing excess reactivity, thereby ensuring compliance with the reactivity control requirements of control drums. In this paper, neutronics calculations and performance analysis of the effect of burnable poisons on a 3 MW yttrium hydride-moderated micro-reactor are carried out using RMC with ENDF/B-VIII database. The neutronic performance of single-layer and double-layer burnable poisons were analyzed, and the results showed that 2 μm-thick ZrB ₂ and 4 μm-thick Gd ₂ O ₃ restrict the maximum excess reactivity to 3,888.2 pcm. Based on the optimized burnable poison, further reactivity control analysis shows that the sixteen core control drums can be divided into two independent reactivity control systems. It is therefore concluded that both systems satisfy the lifetime reactivity control requirements. It is demonstrated that this provides a technically feasible pathway for the reactivity control of in microreactors.