The Integral Inherently Safe Light Water Reactor (I2S-LWR) is a novel reactor concept which aims to apply safety-promoting features typical of small modular reactors (SMRs) to a large pressurized water reactor (PWR) of 3000 MWt, thus providing an option for a passively safe reactor to markets which would find greater economic benefit in a large reactor. Pushing the compact core of an integral reactor to 3000 MWt necessitates several design innovations to remain within safety margins while meeting the goal of increased power density. The I2S-LWR fuel assembly takes on a 19x19 lattice with reduced fuel rod dimensions relative to traditional Westinghouse-type 17x17 PWR fuel assemblies. It is anticipated that the I2S-LWR will eventually employ uranium silicide (U3Si2) fuel instead of uranium oxide (UO2) to improve thermal performance. These unique design features are closely tied to the I2S-LWR core neutronics, thereby necessitating a thorough investigation of reactivity control options. This thesis considers the design of both control rods and burnable absorbers on the basis of the I2S-LWR uranium silicide fuel assembly. Fuel assembly designs are considered with various control rod arrangements and burnable absorber layouts with several candidate absorber materials and concentrations. Viable fuel assembly designs must meet targets for reactivity and power peaking while satisfying constraints on core safety and cycle length. Designs are developed in a heuristic manner, and key performance metrics are processed at each iteration. Characteristics of common optimization algorithms are mimicked at a high level so as to guide the progression of design iterations. The optimized fuel assembly designs produced in this way are recommended for use in core loading pattern design.

In this master thesis a small modular sodium-cooled metal-fuelled pool-type fast reactor design, called SPARC - Safe and Passive with Autonomous Reactivity control, has been designed. The long term reactivity changes in the SPARC are managed by implementation of the the Autonomous Reactivity Control (ARC) system, which is the novelty of the design. The overall design is mainly based on the Integral Fast Reactor project (IFR), which experimentally demonstrated the passive safety characteristics of a metal fuelled, sodium-cooled, pool-type reactor system. Whilst mimicking the passive safety features of the IFR, the vision of the SPARC design is a battery type reactor, which can operate with minimum interference from human actors. In this thesis, two reactor examples have been developed which operate using different fuel compositions. One reactor operates on recycled nuclear waste from today's nuclear power plants, and the other reactor operates on enriched uranium. Both reactors have a thermal power of 150 MW, and are meant to operate for 30 years without refuelling. The design was developed using the ADOPT software, and was simulated in Serpent. Using Serpent, criticality analyses were carried out which show that the ARC system is able to control the long term reactivity changes of the reactors.