MUR Power Uprates

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Mass flow rates are measured using venturis and orifice plates located in steam generator feed water lines. These flow rates provide the basis for the mass and energy balance calculations that are used to control plant output. A high degree of precision and accuracy is required for this measurement.

For most nuclear power plants, the uncertainty in the feedwater venturi measurement reported by the NSSS vendor orarchitect/engineer is approximately r0.5% with the total uncertainty in the calorimetric ±1.5% to ±2.0%.For some generating stations, the reported uncertainty represents a 68% level of confidence (1-sigma) instead of the 95% level of confidence currently recommended in ASME PTC 19.1.

Fouling of these primary elements during plant operation by deposition of corrosion products leads to increased pressure drop across the primary devices. This abnormally high pressure drop produces erroneously highflow rate indications, i.e. the deposits produce a shift in the venturi calibrations.

Very tight controls are imposed by regulating agencies on maximum plant output from nuclear power generating plants. As aresult, lost capacity from venturi fouling is estimated to be 1-2% of the plant rating at most nuclear power plants during the course of a fuel cycle.

Differential Pressure type instruments are subject to drift, bypass, and fouling which often changes over time. This creates the need to calibrate differential pressure type measurements on-line to maximize MW production.

Attention has been focused on the sensitivity of feedwater flow measurement venturis to fouling for a significant time, but,until the availability of UFMs, no practical method to correct for fouling was available.

Caldon LEFM CheckPlus Main Feedwater Measurement System is used for on-line calibration of installed differential pressure instrumentation in AP1000 project. Besides, U.S. NRC approved at opical report that is the basis for the Measurement Uncertainty Recapture Power Uprates (MURPU in short) of reactor thermal power by as much as 1.7% on the basis of improved calorimetric uncertainty achieved by use of Caldon’schordal Leading Edge Flow Meter (LEFM), which is also the only meter approvedby U.S.NRC to conduct the MURPU at present.

There are over 90 nuclear power units have installed Caldon LEFM CheckPlus Main Feedwater Measurement System for power recovery or power uprates all over the world, including Sanmen Nuclear PowerPlant and Haiyang Nuclear Power Plant in China.