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Simplified Approach to Establishing Bounding Main Steam Piping

Author: Robert Stakenborghs and Lindsey Dziuba


Many nuclear power reactors are increasing their electrical output by increasing their licensed thermal power output. This process requires submitting license change request information to the appropriate regulatory body. One of the fundamental changes to a plant operating condition that must occur to provide additional electrical power generation is an increase in the main steam mass flow. This increase in mass flow results in an increase in the fluid velocity at the main turbine stop and control valves. The increased velocity can be correlated to an increase in the piping support loads as a result of a main turbine trip with a corresponding stop valve closure. The increased loads are a concern for the regulatory body as well as the plant owners since these loads occur at some real frequency in a plant. Typically, an overly conservative scaling factor has been applied to these loads, which may result in unnecessary plant modifications. This paper discusses the fundamental transient fluid dynamic process that results in the main steam piping load. A simplified method is provided that more realistically estimates bounding magnitudes of piping support loads versus percentage power uprate. This method will allow plant design engineers to more realistically determine the increase in the main steam piping support loads that result from power uprate conditions.

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