On mechanistic prediction of critical heat flux for nuclear power plants, 4; Current status of experimental studies and measurement techniques for elucidating CHF mechanism in pool boiling

原子力発電所における限界熱流束の機構的予測について,4; プール沸騰におけるCHF機構現象解明に向けた実験研究と計測技術の現状

上澤 伸一郎  

Uesawa, Shinichiro

Estimation of critical heat flux (CHF) is important for safety evaluation in nuclear power plants (NPPs). Generally, the CHF in NPPs is estimated by correlating equations based on experimental data because the CHF mechanism has not been entirely revealed. On the other hand, mechanistic prediction of the CHF is expected by development of measurement techniques and numerical analysis with dramatic improvement in computer performance. In Thermal Hydraulics Division and Computational Science and Engineering Division of Atomic Energy Society of Japan (AESJ), a research expert committee of mechanistic prediction of the CHF in NPPs was established in 2018 to organize knowledge of CHF research and clarify the issues. In this presentation, previous studies of experiments and measurement techniques for elucidating CHF mechanism phenomena in pool boiling are reviewed, and the issues are discussed. To elucidate the CHF mechanism, dynamic behavior of temperature and dry patches on heat transfers surfaces must be clarified. Recently, the temperature and the dry patches on the heat transfer surface can have been measured by two-dimensional distribution. Those experimental results indicated that forming and expanding the dry patches triggered the CHF phenomenon. However, it seems that no conclusion has yet been reached on the mechanism of the expansion of the dry patches and what determines the origin of the dry patch. More detailed measurements and development of the measurement techniques will be needed. On the other hand, as we consider from the viewpoint of CHF at nuclear power plants, the experimental results under high pressure conditions and high subcooled conditions are still few. The studies are expected to progress in the future.