Predictability of safety analysis codes for departure from nucleate boiling in bundle for safety evaluation of massive hydrogen production systems

Abstract

The advanced water reactor was indicated as a candidate for massive hydrogen production system using the water electrolysis method. In order to utilize the advanced water reactor system for hydrogen production, it is crucial to demonstrate the safety of the nuclear system during normal operations and accidents. Departure from nucleate boiling (DNB) is a critical phenomenon in the reactor core which should be addressed to demonstrate the integrity of the nuclear core during normal operations and accidents. Therefore, DNB has a particular importance to the reactor safety and precise prediction has been required for thermal-hydraulic analysis codes including subchannel and safety analysis codes. In this study it has been assessed the DNB prediction capability of thermal-hydraulic safety analysis codes used for the safety evaluation of nuclear reactor system against experimental data. For the assessment, thermal-hydraulic safety analysis codes, MARS-KS and TRACE, have been utilized. The DNB experiments conducted at the NUPEC experimental facility have been employed as a reference experiment for assessment. All experiments with bundle geometries under various steady-state conditions have been analyzed. The results show that both safety analysis codes generally predict the DNB power lower than the experimental database by 20% and the under-prediction occurs systematically with a linear characteristic. It is found that no significant difference in predictability of the DNB occurrence is observed between MARS-KS and TRACE. Therefore, it is concluded that both codes predict DNB conservatively, and MARS-KS and TRACE have almost identical predictability for the DNB occurrence.