Burnup-dependent neutronic-thermal-mechanical-irradiation couplingn method for heat pipe reactor based on cardinal framework

During long-term operation, heat pipe reactors exhibit strong multiphysics coupling effects, encompassing neutronics, heat transfer, structural deformation, and irradiation-induced material evolution. To analyze coupling effects, this study developed a burnup-dependent neutronic–thermal–mechanical–irradiation coupling method for the heat pipe reactor based on the Cardinal framework. The method combines OpenMC with MOOSE-based heat conduction and solid mechanics modules through in-memory coupling, and integrates newly developed irradiation swelling, densification, and creep models through a Python-based external driver. The verifications were performed in two levels. First, a steady-state neutronic–thermal–mechanical calculation was performed using a full-height 1/6 sector model of the MegaPower reactor. The predicted power, temperature, and axial-displacement distributions agree well with the reference results, and the maximum axial displacement is 2.37 cm, approximately 7.1% lower than the reference value of 2.55 cm. Updating the temperature and density fields on the undeformed neutronics geometry produces a total reactivity change of approximately −610 pcm, while geometry reconstruction introduces an additional total geometry-induced reactivity change of approximately −390 pcm. The combined reactivity change relative to the initial undeformed state is approximately −1000 pcm. The results also show that thermomechanical deformation causes noticeable core-power redistribution. Second, an explicit fuel–gap–monolith single-channel model was used for burnup-dependent neutronic–irradiation–thermal–mechanical verification. At 2.0 M W d / k g U , the differences in total strain are 1.39 × 10 - 3 for the fuel and 1.04 × 10 - 3 for the monolith. The principal burnup-dependent trends of fuel swelling, densification, creep, and monolith creep are consistently reproduced. These results demonstrate that the developed method can reproduce both steady-state multiphysics feedback and burnup-dependent irradiation-induced deformation in solid-state heat pipe reactors, providing a foundation for higher-fidelity life-cycle multiphysics analysis.