Spectrum importance model for heavy nuclei synthesis in reactors: Taking 252Cf as an example

We established a spectrum importance model for heavy nucleosynthesis in reactors. A subgroup burnup method, which has no theoretical approximation and can achieve spectrum resolution up to ∼1eV, is proposed for the spectrum quantization. Taking the synthesis of 252 Cf as an example, the transmutation rate of nuclei and synthesis efficiency in each energy region were quantified, and four groups of importance curves were built, which were experimentally verified and tested for universality. Spectrum optimization was carried out based on the importance curves where the positive and negative energy regions were determined. The spectrum filtration technology was proposed to reduce the neutron flux in the negative energy regions, and the single-energy burnup method is proposed to increase the neutron flux in the positive energy regions, achieving the refined adjustment of the neutron flux at multiple single energy points, thus effectively improving the transmutation rate of nuclei and synthesis efficiency (up to 471.01 %). These importance curves reveal the law of nuclei transmutation in all energy regions with high spectrum resolution and build a refined spectrum importance model for heavy nucleosynthesis in reactors, providing theoretical support for high-flux reactor design and irradiation production of transcurium isotopes.