Analyses of Single-Phase Heat Transfer and Onset of Nucleate Boiling in a Rod Bundle With Mixing Vane Grids

Abstract

In the framework of axial offset anomaly risk assessment in Pressurized Water Reactor (PWR) cores, an experimental program involving hydraulic and thermal-hydraulic tests on identical 5x5 bundle geometry was completed. It aimed at developing a consistent set of single-phase heat transfer model and associated onset of nucleate boiling (ONB) wall superheat criterion to further predict the existence and location of boiling zones in a PWR core, using a sub-channel Thermal-Hydraulic (T/H) code. This paper is devoted to the code-based analysis of the experimental data obtained on a bundle equipped with alternating simple support grids and mixing vane grids. Dedicated heat transfer models including a grid enhancement function are developed and the use of Frost & Dzakowic ONB wall superheat criterion is recommended along with these models.