Experimental investigation of the pressure oscillation characteristics of condensation-induced water hammer in a low-height-difference passive heat removal system

As a critical safety barrier for marine floating nuclear platforms (MFNP), the low-height-difference passive heat removal system (LHDPHRS) leverages the infinite heat dissipation capabilities of the marine environment. However, its structural characteristic of low height difference can easily lead to serious condensation-induced water hammer (CIWH) events. This paper presents a visualization experimental device designed to investigate the pressure oscillation characteristics associated with the CIWH phenomenon. Initially, the formation processes of CIWH were identified through visual imaging, which includes stratified flow, wave flow induced by KelvinHelmholtz (K-H) instability, capture and collapse of steam slugs, and reverse flow of cold water. Concurrently, a method for recognizing the CIWH event based on time series images at the fixed pixel position was proposed. Subsequently, our findings on pressure oscillations indicated that as heating power and cold-water temperature increased, both the frequency and peak intensity of these oscillations decreased. Finally, we extracted the volume parameters of isolated steam slugs using an image processing technique. This data was integrated with the condensation collapse rate of steam slugs to establish a theoretical analysis model for predicting CIWH pressure peaks. The discrepancy between theoretical predictions and experimental results ranged from +25 % to -30 %.