Optimization of Burnable Poison Loading for HTGR Cores with OTTO Refueling

• Published in: Nuclear science and engineering 2008-03, Vol.158 (3), p.264-271
• Main Authors: Tran, Hoai Nam, Kato, Yasuyoshi, Muto, Yasushi
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Installations for energy generation and conversion: thermal and electrical energy
• ISSN: 0029-5639; 1943-748X
• DOI: 10.13182/NSE08-A2752

A burnable poison (BP) loading principle has been proposed for once-through-then-out refueling of a high-temperature gas-cooled reactor (HTGR) core with pebble fuel. The principle holds that an axial core power peaking factor can be minimized when k ∞ of the fuel pebbles is kept constant during their axial movement from the top to the bottom of the core by adding BP. This principle has been confirmed numerically using B 4 C with 10 B enrichment of 90% and Gd 2 O 3 with natural content as BP. Spherical particles of B 4 C and Gd 2 O 3 are distributed uniformly in the fuel pebble. The respective optimal radius and number of BP particles are 90 μm and 1650 for B 4 C and 950 μm and 16 for Gd 2 O 3 . Through addition of B 4 C and Gd 2 O 3 , the power peaking factors are reduced from 4.4 to 1.61 and 1.64, respectively. Burnup reactivity swings are reduced from 38% to about 2% in both BP loadings. Because of reduction of the power peaking factors, the maximum fuel temperatures are respectively lower than the maximum permissible values of 1250 and 1600°C for normal operation and depressurization accident.