An Explicit Off-Situ Inversion Method for Neutron Fields in Reactor Core Based on Graph Structure

In the future, advanced reactors will face harsh core environments. Using ex-core detection signals to invert the neutron distribution in the core is important for ensuring the safe operation of the core. The latest data-driven off-situ inversion algorithms do not fully consider the correlations among assembly segments of the reactor core, resulting in the problem of limited accuracy reduction when performing off-situ inversion of the high-resolution neutron field in the reactor core. For this purpose, in this study, an explicit off-situ inversion model of the neutron field in the reactor core based on a graph structure is proposed. By structurally modelling the attribute information of each discretized assembly segment within the reactor core and the relationship information between the assembly segments, the interactions and correlations among the assembly segments are explored to improve the inversion accuracy of the core neutron field. The inversion results in the Chinese lead-based research reactor show that, compared with the previous frameworks, when a single region of the core varied, the maximum relative deviation decreased from 21.8% to 14.01%. When multiple regions of the core varied, the maximum relative deviation decreased from 28.08% to approximately 20%. These results indicate that, by explicitly constructing the relationships between core assemblies, the framework based on the graph structure can increase the inversion accuracy of the core neutron field.