[1M05-07] Advanced Reactor Design

[1M07] Preliminary study of the composite moderator concept in small high-temperature gas-cooled reactors

*Irwan Simanullang¹, Nozomu Fujimoto¹ (1. Kyushu University)

Keywords:small HTGR, Composite moderator, Magnesium oxide, Beryllium oxide, Burnup

The composite composed of an environmentally and radiation-stable continuous matrix containing a highly moderating entrained phase is proposed as a new moderator for the HTGR to replace graphite material. Graphite shows a significant swelling under high irradiation, which leads to microcracking during the operation condition. Therefore, this study aims to investigate burnup performance and safety characteristics of the conceptual core design of the HTR50s using the MgO-BeO as one of the potential composite moderator materials. The Monte Carlo MVP-BURN code was used for burnup calculation. The calculation results showed that the reactor could achieve a burnup of 90 GWd/t with 3.5 years of operation time without refueling. The negative temperature coefficient was reached during the burnup period, and the shutdown margin at the beginning of life (BOL) was 8.6 %Δk/k.