Analysis of PRV Stability In Relief Systems Part III

As a result of increasing steam flow rates, several boiling water reactor (BWR) nuclear power plants have recently experienced the excitation of acoustic standing waves in closed side branches, e.g., safety relief valves (SRVs), due to vortex shedding generated by steam flow in the main stream lines. Flow past a valve entrance cavity excites a standing wave, resulting in noise and vibrationii. A similar tone is produced when air is blown across the mouth of a glass bottle.

The amplitude of the acoustic pressure waves can be several times higher than the dynamic pressure present in the system (see Figure 1 and Figure 2). The acoustic waves propagate in the steam lines, eventually reaching sensitive components such as steam dryers and turbine stop valves. In addition, the acoustic waves generated in the side branches may generate vibration problems locally and may lead to complications such as valve-seat wear. Therefore, the structural components are subjected to high-cycle fatigue loads, which over time may severely impact those components’ functionality and safety.

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