Reactor core conceptual design for a scalable heating experimental reactor, LUTHER

Abstract

In this thesis, the first conceptual design and a preliminary study of LUT heating experimental reactor (LUTHER) for a 2 MWth power are presented. Additionally, commercial-sized reactor designs for 24 MWth and 120 MWth powers are also studied and discussed. LUTHER is a scalable light-water pressure-channel reactor designed to operate at low temperature, low pressure and low core power density. The LUTHER core utilizes low enriched uranium (LEU) to produce low-temperature output, targeting specifically the district heating demand in Finland. LUTHER is developed to contribute to decarbonizing the heating and cooling sector, which is a more significant greenhouse gas emitter than electricity production in the Nordic countries.

The main principle in the development of LUTHER is to simplify core design and safety systems, which, along with using commercially available reactor components, would lead to lower fabrication costs and enhanced safety. LUTHER also features a unique design with moving fuel assemblies used for reactivity control, fuel burnup compensation and reactor shutdown. The 2 MWth LUTHER core is designed to experiment and demonstrate the novel means of reactivity control and feasibility of a pressure-channel district heating reactor. However, the 2 MWth core seems too small to be feasible as an operating operator. Recommendation for increasing the core power of the demonstration reactor to 6 MWth is proposed.

2-dimensional (2D) and 3-dimensional (3D) fuel channels with fuel assemblies inside and reactor cores are modeled with the Serpent Monte Carlo reactor physics code. Different reactor design parameters and safety configurations are calculated and assessed, regards the core’s basic thermal hydraulics and reactor physics. Preliminary results show an optimal basic core design, a good neutronic performance and feasibility of controlling reactivity by moving fuel assemblies, eliminating the use of conventional control rods and soluble poisons, such as boron.