Flattening of burnup reactivity in long-life prismatic HTGR by particle type burnable poisons

Particle-type Burnable Poisons for Thorium-based Fuel in HTGR

“…The use of burnable poison (BP) is one of the conventional approaches to control the reactivity in the HTGR. The use of particle-type burnable poison in both pebble bed reactors and prismatic HTGRs have been reported to effectively control the high excess reactivity and flatten the reactivity swing throughout the whole burnup operation [15][16][17][18]. However, the results were confirmed in HTGRs using uranium nuclear fuel, not in HTGRs using thorium-based fuel.…”

“…High excess reactivity is undesirable in the reactor safety design because it can lead to a prompt supercritical situation in the reactor. Thus, we introduced combinations of B 4 C and Gd 2 O 3 particles or B 4 C and CdO particles as burnable poisons, which can effectively control reactivity in a prismatic HTGR even when using 20 wt% 235 U nuclear fuel [16][17][18]. These burnable poisons compensated for the high excess reactivity in the thorium fuel based HTGR in this study.…”

Small, long-life high temperature gas-cooled reactor free from prompt supercritical accidents by particle-type burnable poisons

“…Therefore, the effective macroscopic absorption cross section in Equation (1) can explain the depletion behavior of BP particles only at the initial stage of burnup [6]. In this study, we examined the combined compositions of BP particles made from two materials, which have been reported in previous studies [7,8]. The combined use of B 4 C and Gd 2 O 3 particles and the other combination of B 4 C and CdO particles can give satisfactory results in reactivity control by minimizing the excess reactivity until it is less than 1$, and by flattening the reactivity swing when applied in the HTTR [7,8].…”

“…In this study, we examined the combined compositions of BP particles made from two materials, which have been reported in previous studies [7,8]. The combined use of B 4 C and Gd 2 O 3 particles and the other combination of B 4 C and CdO particles can give satisfactory results in reactivity control by minimizing the excess reactivity until it is less than 1$, and by flattening the reactivity swing when applied in the HTTR [7,8]. Hence, the application of BP particles of two materials in the higher thermal power of the 100-MW th HTGR with larger sized core diameter is required to investigate this combination's capability in reactivity control.…”

“…The application of poison particles has also been introduced in a prismatic HTGR by Obara et al [7,8], whose study showed that the utilization of BP particles instead of BP rods in a HTTR can control the reactivity within 1$ in the reactor core of a block-type gas-cooled reactor. On comparing between an original BP rod approach, in which the BP rods are inserted in the hole of the graphite block, which is used in the HTTR with 10 wt% enriched uranium on average, and the use of BP particles in the HTTR with more highly enriched uranium (20 wt%), it was found that the conventional BP rods can control the reactivity swing within only 2.6% k/k, whereas the use of BP particles with higher enrichment in the same reactor design, causing much higher excess reactivity, can effectively control the swing of reactivity within 1$ or approximately 0.67% k/k by withdrawing all of the control rods [1,7,8]. Given this background, the purpose of the present study is to show a reactor concept that has no possibility of a prompt supercritical accident during an operation in a small, long-life HTGR using particle-type BP and criticality control by the core temperature.…”