MODELLING AND NEUTRONIC DESIGN OPTIMIZATION OF A HEAT PIPE COOLED MICRO NUCLEAR REACTOR

Abstract

This thesis presents the modelling and neutronic design optimization of a 5 MWt heat pipe-cooled Micro Nuclear Reactor (MNR) developed for deployment in remote and off-grid environments. Operating within a fast and intermediate neutron energy spectrum, the reactor is inspired by the Los Alamos National Laboratory’s Design A concept but incorporates substantial enhancements to improve compactness, safety, and performance. Key innovations include the use of TRISO fuel embedded in a beryllium matrix, passive cooling through sodium heat pipes, and a hexagonal core layout designed for long-term, maintenance-free operation. Extensive neutronic analyses were conducted using the OpenMC Monte Carlo code to evaluate neutron flux distributions, reactivity behaviour, fuel temperature coefficients, and depletion characteristics. Several design optimizations were implemented to achieve and sustain criticality despite the lower fissile content of TRISO fuel, such as pitch adjustment, cladding removal, and matrix material selection. The finalized core features 462 unit cells, surrounded by an alumina reflector and regulated by 12 hafnium hydride control drums and a central control rod to ensure precise reactivity control. This study demonstrates the feasibility of a compact and inherently safe microreactor capable of 20 years of autonomous operation. Its robust, passively cooled design offers a promising solution for energy delivery in remote, austere, or emergency settings, supporting the broader goals of sustainable and decentralized nuclear power deployment.