Multi-region rewetting analysis of a PWR fuel slab using an improved-lumped model

This research constructs an analytical framework to study the behavior of a Pressurized Water Reactor (PWR) fuel slab during core rewetting following a hypothesized Loss of Coolant Accident (LOCA). The fuel is modeled as a semi-infinite slab without internal heat generation. The Classic Lumped System Analysis (CLSA) and the Improved Lumped System Analysis (ILSA) with Hermite approximations are applied in the transversal direction of the flow, assuming uniform heat transfer coefficients within each zone. This approach simplifies the analysis to a one-dimensional longitudinal heat conduction equation. The analysis divides the system into a dry region, multiple boiling sub-regions, and one wet region. A quasi-steady state regime with a constant rewetting velocity is assumed, establishing a moving reference frame at the rewetting front, also known as quench front. Analytical solutions for the different regions are developed, with the rewetting velocity determined by matching these solutions at the interfaces between the regions. Additionally, a relationship between the rewetting velocity and the wet region Biot number is established. The results of the model show good alignment with existing literature studies and experiments.