Power reconstruction in hexagonal-assembly small reactor using thin-plate spline and in-core detector response

The three-dimensional power distribution (3DPD) of a reactor core is an important indicator of reactor operating conditions, and its accurate reconstruction is essential for core monitoring and safe operation. Compared with conventional large reactors, small reactors with hexagonal fuel assemblies exhibit stronger neutron leakage and more complex spatial power characteristics, increasing the difficulty of power reconstruction. To address this issue, this study investigates 3DPD in a hexagonal-assembly small pressurized water reactor using the thin-plate spline (TPS) method combined with in-core detector response functions. The results show that the in-core detector response exhibits strong spatial localization characteristics. Radially, the detector response is mainly concentrated within the third ring of neighboring assemblies (∼15 cm). Neglecting detector response leads to significant reconstruction errors. By incorporating detector response functions, the TPS method effectively suppresses reconstruction deviations under different burnup levels, keeping all post-reconstruction relative errors within the commonly adopted 8% acceptance criterion. The proposed method demonstrates good applicability to hexagonal fuel assembly 3DPD reconstruction in small reactors.