AP-1000 fuel assembly performance with cadmium oxide as a new burnable poison

ABSTRACT

One of the main nuclear reactor design problems is finding an efficient method for reactivity control. Boron-free small modular reactors and long-life pressurized water reactors need proper neutron absorbers to suppress large initial reactivity and gentle reactivity variation during reactor operation. In this paper, AP-1000 fuel assembly is used to investigate the effect of using cadmium and enriched Cd113 as burnable poisons. The reactivity behavior of the AP-1000 fuel assembly is of interest. The DRAGON code calculates the neutronic performance of the natural and enriched UO₂-CdO. The investigation is performed from the standpoint of initial reactivity, reactivity swing, pin power peaking factor, and cycle length. As a further check, the impact of the CdO on the MTC results is also explored. Moreover, the results are compared with those of gadolinia-bearing rods. Fully enriched cadmium oxide (enriched in Cd113) provides 10.5% more initial reactivity suppression than that of gadolinia fully enriched by Gd157 while reaching almost the same cycle length. Also, using cadmium enriched in Cd113 leads to reducing parasitic absorption. The reactivity swing of the case fully enrichment of Cd113 is 21% lower than the case with natural cadmium rods. It is also found that the residual binding of the CdO with 100%Cd113 enrichment and Gd₂O₃ with 100%Gd157 enrichment are 0.002928 and minus 0.0026 respectively. Moreover, it is seen that, the normalized pin power for 2 w/o concentration of CdO fully enriched Cd113 has been increased by 3.3% relative to the case with Nat. Cd.

KEYWORDS:

• Cadmium
• AP-1000
• reactivity
• swing
• residual binding

Disclosure statement

No potential conflict of interest was reported by the author.

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Farrokh Khoshahval

Farrokh Khoshahval is with Reactor and Nuclear Safety Research School, Nuclear Science and Technology Research Institute (NSTRI). He received his BSc degree in Electrical Engineering and Master’s and PhD degrees in Nuclear Engineering from Shahid Beheshti University, Iran. His research areas include neutronic, thermal-hydraulic analysis, nuclear fuel management and heuristic optimization methods.