REACTOR PHYSICS EXPERIMENT IN A GRAPHITE-MODERATION SYSTEM FOR HTGR Y. Fukaya, M. Goto, S. Nakagawa, K. Nakajima, K. Takahashi, A. Sakon, T. Sano and K. Hashimoto EPJ Web Conf., 247 (2021) 09017 Published online: 22 February 2021 DOI: 10.1051/epjconf/202124709017