High conversion Th-U233 fuel for current generation of PWRs: Part I – Assembly level analysis

Abstract

This study explores the possibility of designing a high conversion (HC) Th-U233 core for current generation of Pressurized Water Reactors (PWRs). Increasing the conversion ratio in existing PWRs can potentially improve the utilization of natural resources, through the exploitation of vast thorium reserves and reduction in natural uranium demand.HC can be achieved through the use of heterogeneous seed-blanket (SB) Th-U233 fuel assembly design where the supercritical seed works as a neutron supplier, while the subcritical blanket acts as U233 breeder. One of the main challenges associated with the heterogeneous SB fuel assembly designs is a significant power imbalance between the seed and blanket regions caused by the concentration of fissile material primarily in the seed zone and consequently requiring a substantial reduction in the core average power density.The main objectives of the current work are: (1) to design a HC SB Th-U233 fuel assembly which is directly retrofittable into existing PWRs without introducing significant modifications into the core and plant design; (2) to estimate the reasonably achievable core power density level at which reactor safety is not compromised by performing 3D coupled neutronic and thermal–hydraulic (T–H) analysis of a typical PWR core fully loaded with HC Th-U233 SB fuel.Part I of the two-part paper presents the results of the assembly-level parametric study aiming at the selection of a number of SB fuel assembly configurations for the following whole-core analysis. The assembly configurations are selected according to their potential to satisfy the specified fuel cycle requirements and comply with the T–H safety limits.The results of the 3D full core analysis are reported in Part II of the paper.