Core Heat Transfer Coefficients Immediately Downstream of the Rewetting Front during Anticipated Operational Occurrences for BWRs

A heat transfer coefficient (HTC) model was developed for the prediction of post-boiling transition (post-BT) behavior that might occur during anticipated operational occurrences (AOOs) for boiling water reactors (BWRs). The model development was based on measurements of heat transfer coefficient, liquid droplet deposition rate, and droplet concentration in our experiments conducted at high pressure. The model focused on the heat transfer near the rewetting front where the cooling by droplet deposition significantly affects the propagation behavior of a liquid film. The correlation by Sugawara was validated for the prediction of the deposition by using the experimental data. The model was also expressed as a function of the distance from the rewetting front to use in analytical models for the rewetting propagation. Both expressions of the present model successfully predicted our experimental data simulating the BWR thermal-hydraulic conditions.     

燃料棒周向导热对超临界水堆堆芯子通道分析的影响

本文在子通道程序的燃料棒模型中引入三维导热方程,使该模型能用来模拟燃料棒的周向导热情况。采用改造后的子通道程序对混合谱超临界水堆设计中的两种燃料组件结构进行计算分析,研究燃料棒周向导热对超临界水堆燃料组件子通道分析的影响。结果表明：热谱组件的子通道计算中,燃料棒周向导热的影响不能忽略;快谱组件的子通道计算中,燃料棒周向导热的影响基本可忽略。     

Rewetting front propagation under anticipated operational occurrences for boiling water reactors – development of two-dimensional analytical model

An analytical model to predict a rewetting velocity applicable to high pressure and high flow rate condition during anticipated operational occurrences (AOOs) is developed by applying Wiener–Hopf technique coupled with appropriate kernel substitutions. The model considers the effects of enhanced cooling in the vicinity to liquid film front termed “precursory cooling” and heat input from fuel pellets on back side of wall as boundary conditions of a heat conduction equation. A simplified two-dimensional model neglecting an effect of axial heat conduction is also proposed. It is found through the comparison among the models and experimental data that the contribution of the heat conduction in the wall-depth direction is essential in the prediction of the rewetting velocity at the thermal-hydraulic condition simulating AOOs and the axial heat conduction has little influence when an enhanced heat transfer coefficient in the dried-out region is appropriately given as a function of distance from the liquid film front.