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<p>Knowing the precise relationship between fuel loading and reactivity is essential for guiding reactor criticality extrapolation and online refueling in molten salt reactors (MSRs). This study aims to explore and explain the linear relationship between reactivity and the reciprocal of uranium concentration in thermal-spectrum MSRs. By applying neutron balance theory, we analyzed the neutron absorption cross sections of various nuclides in single-lattice models with varying fuel concentrations. Our findings reveal a simple linear correlation between reactivity and the reciprocal of uranium concentration, which can be explained from the perspective of nuclear reaction cross sections that adhere to the 1/<i>v</i> law in the thermal neutron spectrum. Furthermore, we identified that the neutron absorption single-group cross sections of structural materials and carrier salts exhibit an approximately linear relationship with the fission single-group cross section of <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(^{235}\)</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mrow /> <mn>235</mn> </mmultiscripts> </math></EquationSource> </InlineEquation>U; similarly, the reciprocal of <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(^{235}\)</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mrow /> <mn>235</mn> </mmultiscripts> </math></EquationSource> </InlineEquation>U’s fission cross section exhibits an approximately linear relationship with uranium concentration. This linear relationship deviates as the volume fraction of molten salt increases, due to a greater proportion of neutrons being captured in the resonance energy spectrum. However, it remains valid for molten salt volume fractions up to 25% and demonstrates broad applicability in the physical design and operation of thermal molten salt reactors.</p>

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Linear relationship between reactivity and the reciprocal of uranium concentration in thermal-spectrum molten salt reactors

  • 期刊论文

  • 发表日期：

    2026年1月3日

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  • Chang-Qing Yu,
  • Gui-Feng Zhu,
  • Shu-Yang Jia,
  • Yang Zou,
  • Rui Yan,
  • Jian Guo,
  • Ya-Fen Liu,
  • Bo Zhou,
  • Xue-Chao Zhao,
  • Xiao-Han Yu

摘要

Knowing the precise relationship between fuel loading and reactivity is essential for guiding reactor criticality extrapolation and online refueling in molten salt reactors (MSRs). This study aims to explore and explain the linear relationship between reactivity and the reciprocal of uranium concentration in thermal-spectrum MSRs. By applying neutron balance theory, we analyzed the neutron absorption cross sections of various nuclides in single-lattice models with varying fuel concentrations. Our findings reveal a simple linear correlation between reactivity and the reciprocal of uranium concentration, which can be explained from the perspective of nuclear reaction cross sections that adhere to the 1/v law in the thermal neutron spectrum. Furthermore, we identified that the neutron absorption single-group cross sections of structural materials and carrier salts exhibit an approximately linear relationship with the fission single-group cross section of \(^{235}\) 235 U; similarly, the reciprocal of \(^{235}\) 235 U’s fission cross section exhibits an approximately linear relationship with uranium concentration. This linear relationship deviates as the volume fraction of molten salt increases, due to a greater proportion of neutrons being captured in the resonance energy spectrum. However, it remains valid for molten salt volume fractions up to 25% and demonstrates broad applicability in the physical design and operation of thermal molten salt reactors.