USNRC gate valve test results challenge flexible wedge gate valve, motor operating sizing equation

The Flexible Wedge Gate Valve Qualification and Flow Interruption Test Program is investigating the ability of selected process valves in boiling water reactors (BWRs) to isolate the containment at high energy pipe break conditions. This paper presents the results of testing to assess valve and motor operator performance under varying pressures and fluid conditions and to assess the effectiveness of typical motor operator sizing methods used by the nuclear industry, specifically the stem force equation. Six isolation valves were tested representative of 6-in. and 10-in. valves used in BWR reactor water cleanup (RWCU) systems and high pressure coolant injection (HPCI) and reactor core isolation cooling (RCIC) turbine supply steam lines. The studies included six qualification tests and 17 flow interruption tests. Seven of the flow interruption tests were design basis tests and the remainder were parametric studies designed to investigate the effects of pressure, fluid density, and temperature on valve performance. The results indicate that the phenomena taking place inside the gate valve are much more complex than previously thought. For instance, the actual disc factor is much higher than calculations using the stem force equation indicate. It also appears that valves closing on a steam load do not require as much force to close as valves that must close on a water load. And finally, the current industry stem force equation is incomplete