NRC test results and operations experience provide insights for new gate valve thrust equation

The Idaho National Engineering Laboratory (INEL) is performing motor-operated valve (MOV) research in support of the US Nuclear Regulatory Commission's (NRC's) efforts regarding Generic Issue 87, 'Failure of HPCI (High-Pressure Coolant Injection) Steam Line Without Isolation,' and Generic Letter 89-10 (GL 89-10), 'Safety-Related Motor-Operated Valve Testing and Surveillance.' This paper presents the results of testing to assess valve and motor operator performance under varying pressures and fluid conditions. This effort included an examination of the methods used by the industry for predicting required valve thrusts and research to provide guidelines for the extrapolation of in situ test results to design basis conditions. This research has identified several inconsistencies in the existing industry stem thrust equation and challenged the overly simplistic assumptions inherent in the use of the equation. This paper discusses development of a new equation whereby conservative stem thrust estimates can be calculated for some flexwedge gate valves, that is, those classes of valves whose operational characteristics have been shown to be predictable. The authors also present a method whereby the results of testing of such valves at low differential pressure can be used to estimate valve response at up to design basis conditions