Correction factor development for the 2006 Groeneveld CHF look-up table for rectangular channels under low pressure

Abstract

Similar to commercial nuclear reactors, research reactors are recommended to be designed with sufficient safety margins for thermalhydraulic issues such as critical heat flux (CHF) in both normal and accident conditions. In the MARS-KS system code, developed based on RELAP5, the 2006 Groeneveld CHF look-up table (Groeneveld et al., 2007) is adopted to predict CHF for plate-type fuel. The applicability of this table to CHF in rectangular channels for high pressure conditions of over 40 bar has been confirmed (Choi et al., 2015); however, its applicability to pressure conditions under 40 bar has yet to be clarified. While Sudo and Kaminaga previously suggested a rectangular CHF model for a wide experimental range, some notifications have indicated the inclusion of flow excursion data in their model. In this paper, a rectangular channel CHF database was constructed for wide experimental ranges and used to assess the 2006 Groeneveld CHF look-up table and Sudo-Kaminaga correlation to confirm their applicability to rectangular channels under low pressure. Then, with several parameters selected by the Random Forest method in the R package (Reynolds number, quality, aspect ratio, diameter ratio, and length over diameter), a new correction factor was suggested by applying a non-linear regression method from a statistical software package to correct the CHF values in the CHF look-up table for rectangular channels. Results confirmed that the CHF LUT with the newly suggested correction factor is capable to predict CHF in rectangular channels.