Ultrasonic downcomer flow measurements for recirculating steam generators

•Measuring recirculating flow in nuclear steam generators provides useful information.•Flow measurements shed light on component performance and degradation mechanisms.•Commonly used ultrasonic technology and application methods are described.•Results of measurements at several power reactors are summarized.•Potential improvements in reliability and flexibility of application are suggested.

Measurements of downcomer flow in nuclear steam generators can provide unique fitness for service and performance indicators related to overall thermalhydraulic performance, safety related secondary-side setpoints and certain forms of degradation.This paper reviews the benefits of downcomer-flow measurements to nuclear power–plant operators, and describes methods that are commonly used. It summarizes the history and state-of-the-art of the most widely used technology, non-intrusive ultrasonic systems, including field applications at several nuclear power plants. It also describes the technical challenges that remain, and summarizes recent technical developments and future improvements.