Coupled neutronic, thermal-mechanical and heat pipe analysis of a heat pipe cooled reactor

Abstract Heat pipe cooled reactors are solid-state, high temperature reactors with significant thermal expansion which influences the neutronics and thermal analyses. The heat pipe operating conditions determine the heat transfer rates and temperature distribution which then affect the core neutronic and thermal–mechanical behavior, especially during heat pipe failure accidents where the radial heat flux is uneven. A two-phase two-dimensional heat pipe model was developed and coupled to a previous neutronic and thermal–mechanical (N/T-M) model. The coupled neutronic, thermal–mechanical and heat pipe heat transfer (N/T-M/HP) strategy is described here with a focus on the iteration schemes, physical mapping and geometry reconstruction. The coupled N/T-M/HP method was then applied to the KRUSTY heat pipe cooled reactor, an experimental solid-state reactor designed to power space missions. The power distribution and reactivity predicted by the coupled method are validated against previous simulations for the KRUSTY design. The heat pipe model predictions are compared with heat pipe experiments which show that the predicted heat pipe wall temperature is within 30 K of the measured temperatures. A steady-state normal operating case and a single heat pipe failure accident were then simulated to show the redundancy and reliability of the solid-state reactor. For the normal case, the thermal–mechanical feedback is ∼850 pcm from the cold state to the hot state. The heat transfer rate into each heat pipe is very stable during the iterations. For the single heat pipe failure accident, the heat pipes adjacent to the failure area are the most affected, with those heat loads increasing from 500 W to 640 W and an operating temperature rising by 16 K. In addition, the single heat pipe failure accident significantly increases the stress concentration in the fuel contacted with the failed heat pipe wall, with the peak stress increasing from 53 MPa to 80 MPa, which is very close to the yield stress. Therefore, the mechanical performance of the solid-state reactor should be carefully analyzed during design and operation.