Thermal Hydraulic Modeling of Solid-Fueled Nuclear Thermal Propulsion Reactors Part II: Full-core Coupled Neutronic and Thermal Hydraulic Analysis

This paper focuses on the extension and application of the previously validated thermal-hydraulic engineering code ntpThermo to perform multi-channel analysis for full-core coupled neutronic and thermal-hydraulic sim-ulations. This paper also introduces the Basilisk code, which enables coupled full-core neutronic and thermal --hydraulic simulations by integrating Serpent, the continuous energy Monte-Carlo neutron transport code, and ntpThermo within a flexible object-oriented framework. Today, limited data exists pertaining to coupled mul-tiphysics analysis of low-enriched uranium nuclear thermal propulsion reactors. More specifically, the impact of thermal-hydraulic feedback on the neutronic solution for full core applications is not well quantified. In this paper full-core coupled neutronic and thermal-hydraulic simulations are performed to ascertain the importance of thermal-hydraulic feedback on the predicted reactivity and local power distributions. The reactor design analyzed adheres to the current industry ground rules in an effort to provide useful insights for the current in-dustry design effort. The results in this paper demonstrate that thermal-hydraulic feedback must be considered to accurately predict reactivity; otherwise, errors on the order of hundreds to thousands of pcms can be observed. Additionally, neglecting thermal-hydraulic feedback can trigger inconsistencies between the radial power dis-tribution and the fuel orificing pattern. A design approach that doesn't account for thermal-hydraulic feedback can lead to a final design that may experience thermal failure via excessive fuel temperatures, and would require a reduction of reactor power. The latter will cause a subsequent decrease in exit propellant temperatures and thus specific impulse of the rocket engine. Sensitivity studies were conducted to determine the importance of specific thermal-hydraulic fields and revealed that the local moderator temperature has a notable impact on the local power distributions.