Research on the application of burnable poison ZrB2 and Gd2O3 in a small modular lead-based thermal reactor

Highlight• Analysis of BPs in a small modular lead-based thermal reactor was carried out. • A small modular lead-based thermal reactor was constructed with the SuperMC code. • The burnup characteristics of ZrB₂ and Gd₂O₃ were investigated and compared. • An optimized core was proposed and main neutronics parameters were analyzed. A lead-based reactor with thermal or epithermal spectra is considered to be a good choice for small modular reactors design. Beside the safe and better thermal property of lead coolant it also takes the advantage of the smaller critical mass characteristics of thermal reactor. However, it needs to control the substantial amounts of excess reactivity at the beginning of core life which is essential to get a long-life cycle. Therefore, choosing the appropriate burnable poison material and optimizing its arrangement is a big concern during the design of a small modular lead-based thermal reactor. In this article, the analysis on use of burnable poison in a small modular lead-based thermal reactor has been carried out to achieve effective control of reactivity. The burnup characteristics of burnable poison ZrB₂ and Gd₂O₃ were investigated and compared. The results show that ZrB₂ is better than Gd₂O₃ for flatting the k_eff curve, while the depletion rate of Gd₂O₃ is much faster than ZrB₂. Reducing the poison content in poison rods and increasing the number of poison assemblies can speed up the poison depletion. Based on the results, an optimized core (with the use of burnable poison) which can give a more flat k_eff curve with the burnup reactivity swing less than 3303 pcm was given. And the influences of the burnable poison on the main parameters of the optimized core scheme such as power distribution and reactivity coefficient were analyzed. The results show that with the use of burnable poison, the radial power distribution becomes more flat and the coolant void effect and fuel temperature reactivity become more negative.