Nuclear Engineering and Technology

Korean Nuclear Society (한국원자력학회)
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Analyses on the recriticality and sub-critical boron concentrations during late phase of a severe accident of pressurized water reactors

  • Received : 2023.02.20
  • Accepted : 2023.06.10
  • Published : 2023.09.25
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Abstract

The potential for recriticality and sub-critical boron concentrations is analyzed during the relocation of the fuel rods in the assembly, which we call late phase of a severe accident, via coupling between MELCOR and whole-core Monte Carlo analyses by Serpent 2. The recriticality, initiated during the early phase, is found to maintain when the fuel assemblies containing intact fuel rods are submerged by the cooling water. It is also found that the effect of the negative reactivity insertion via remaining fission products in the fuel debris increases as the burnup increases. The sub-critical boron concentrations during the late phase are found to be 76~544 ppm lower than those during the early phase. Therefore, it can be concluded that the boron concentration that prevents recriticality not only during the early phase but also during the late phase is the sub-critical boron concentration during the early phase.

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Acknowledgement

This work was supported by the Nuclear Safety Research Program through the Korea Foundation Of Nuclear Safety (KoFONS) using financial resources granted by the Nuclear Safety and Security Commission (NSSC) of the Republic of Korea (No. 2106007). The authors also would like to thank the reviewers for giving very detailed and useful reviews to strengthen the paper.

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