| Summary: | Missions to Mars with eventual establishment of a Mars base/colony will require a versatile and consistent transportation method between Earth and Mars. Nuclear thermal propulsion (NTP) is well suited to be the main propulsion mechanism for interspace travel due to its high specific impulse. In order to develop a robust NTP system, the reactor core must be able to prevent a supercritical state from occurring in the event a launch failure or an atmospheric reentry results in the reactor entering a body of water. In this accident, the flooding of the hydrogen coolant channels causes a surge in reactivity, which can be harmful to the environment around the reactor. This work focuses on investigating the effectiveness of various design options in mitigating a submersion criticality accident and their impacts on the fuel lifecycle for a modified version of the Space Capable Cryogenic Thermal Engine (SCCTE) reactor core. Multiple design options were considered such as enhanced accident tolerant control drums, coolant channel radius adjustment, telescoping control rods, and the implementation of a spectral shift via enrichment zoning. Analysis was performed using Monte-Carlo code SERPENT 2.1.3.1, supported by 1D thermal hydraulics modeling when necessary. Both fuel lifecycle and peaking factors are included as metrics for comparing each method’s effectiveness. The analysis determined that many of the design options limited the core’s fuel lifecycle, and that only control drum enhancement and the employment of telescoping control rods were independently capable of keeping the reactor subcritical in the event of a water submersion. While some designs were feasible in their mitigation of the submersion worth, additional thermal analysis is required to verify their compatibility with the high temperatures present within the core.
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