Non-lntrusive Downcomer Flow Measurements: A Means of Monitoring Steam Generator Performance

Abstract

Nuclear plant reliability depends directly on steam generator performance. Downcomer flow is a good monitor of steam generator performance. It provides information critical to the efficient and safe operation of steam generators as determined by the recirculation ratio and water inventory. In addition, reduced downcomer flow may indicate steam generator crudding or inadequate chemical cleaning. This paper describes the application of ultrasonic technology to measure flow velocity in the downcomer annulus during operation. The technique is non-intrusive since the measurements are taken with ultrasonic transducers mounted on the outer shell of the steam generator. Successful application of this technique required development in several areas - high temperature couplant, signal quality, transducer performance and reliability and remote monitoring. The effects of carry under, obstacles in the downcomer annulus, temperature variation, and wall thickness are also discussed in this paper. The results of measurements from 0 to 100% power in the Darlington nuclear station are presented. The results are compared to thermalhydraulic calculations. A second ultrasonic technique has recently been successfully tested at operating conditions with void in the flow. This new technique is also presented in this paper.