Various solutions for the pressurizer safety and pressure operated relief valve discharge piping system hydraulic transient problem

As a result of the Three Mile Nuclear Power Plant Incident, the NRC issued NUREG-0737, which requires all operating plant licensees and applicants to conduct testing to qualify the reactor coolant system safety and relief valves under expected operating conditions for design-basis transients and accidents. In addition to the qualification of valves, the functionality and structural integrity of the existing discharge piping system (pipe, pipe components and supports) must also be demonstrated on a plant-specific basis. In response to these requirements, a program for the performance testing of the pressurized water reactor (PWR) safety and relief valves was formulated by the Electric Power Research Institute (EPRI). The testing showed that large hydrodynamic loads are generated in the valve discharge piping system when the valve activation involves the discharge of cold water (generally less than 180 F). Also, analyses have shown that these hydrodynamic loads produce elastic stresses in the piping system that exceed code allowables. This paper presents the findings related to nine different options that have been considered for the resolution of the large hydrodynamic load problem at four different Nuclear Power Plants. The method of analyses and the pertinent results (hydrodynamic loads and/or stresses) are discussed for the options. Comparisons for various options are presented and the options that have been implemented are identified. The contents of this paper span the ten year period from 1982 to 1992