Fundamental Design Considerations for Nuclear Space Power Systems

Abstract

This thesis aims to set forth the fundamental differences in the design methodology and system engineering of Nuclear Space Power (NSP) reactor and electrical generation systems versus terrestrial designs.
We begin by comparing NSP with Solar Photo-Voltaic (SPV) systems and their evolution in space, intending to identify and justify urgent and necessary applications of NSP generation. Then, we briefly review data on fuel forms and reactor materials, eliminating materials unsuitable for thermal spectrum reactors. Noting that heavy-duty materials may serve as fuel cladding, we discuss the reactor costs, mass, longevity and ease of manufacture. After that, we develop simple thermal hydraulics models of a Pin-in-Cell fuel element and discuss reactor coolant selection. Introducing our rudimentary heat engine models of the Brayton and Rankine cycles, we derive the mathematics describing the system-wide behaviour of a Brayton and Rankine cycle coupled to a radiator. Our insights from thermodynamic and thermal hydraulic analysis lead to nuclear engineering concepts that assist with building a working reactor. We design parametric simulation models using OpenMC’s Python API, providing us with the optimum Moderator to Fuel (MF) volume ratios, MF mass ratios, and 3D reactor core data for high-temperature monolithic and composite hydride moderators.
Herein, we also demonstrate a novel NSP system design approach where regulatory justification, logistics and spacecraft thermal design principles are exploited to enforce fundamental constraints on the NSP system design. The NSP system design workflow we adopt relies on open-source, easy-to-use and computationally inexpensive software. Ultimately, we aim to provide a solid introduction to the subtleties of designing a nuclear power system to operate for long periods in space while being compact, lightweight and relatively inexpensive.   Errata: Page 80: "Yttrium hydride produces the lightest critical cores, the 7-ringed variant being close to 500 Kg minimum mass." is incorrect as zirconium hydride produces critical cores with less fuel elements. The sentence should read: "Overall, zirconium hydride produces the lightest critical cores, with the 5-ringed variant being close to 270 kg minimum mass."