Optimized control rod designs for Generation-Ⅳ fast reactors using alternative absorbers and moderators

摘要

The characteristics of Generation-IV fast reactors strongly impact the design of its control rods. The traditional control rod is a cluster of vented pins with boron carbide (B4C) as the absorber. Due to the gas release, the neutron-induced swelling, the melting risk, and the high loss of the reactivity worth, B4C impact the safety performance of control rods and thus limit their operating lifetime.Various alternative absorbers to B4C are assessed in detailed designs according to their neutronic performance, safety performance, and waste management. The hafnium diboride (HfB2) process a high thermal conductivity, a high melting point, and a small neutron-induced swelling, which contributes to an enhanced safety performance. The europium oxide (Eu2O3) process a very small loss of the absorption ability for a long-time utilization. Hafnium hydride (HfH1.62) has a good neutronic performance, but its hydrogen desorption issue should be further investigated.The absorption cross-section decreases generally with the neutron incident energy. Moreover, an important spatial self-shielding effect is found in the control rod, which leads to a peak temperature and peak burnup in the outer zone while a non-optimized utilization of absorber in the inner zone. In this work, the hydrogen-containing moderator is used in independent pins to replace some absorber pins in control rods. The moderator is able to increase significantly the absorption ability of Eu2O3 and of gadolinium oxide (Gd2O3). The moderator optimizes the utilization of absorbers, such as HfB2 and B4C, and save their investment. By homogenizing the absorption distribution, the application of moderators has only a limited influence on safety performance or waste management. (C) 2019 Elsevier Ltd. All rights reserved.