July-August 2019 NPJ

Nuclear Plant Journal, July-August 2019 NuclearPlantJournal.com 41 Greg Morton Greg Morton is Chief Technical Officer (CTO) at AMS, responsible for all software and hardware development activities for the ompany. He directs he AMS software and hardware development departments, upervising a team of 20 engineers, developers, and upport personnel. Since joining AMS in 1995, he has been responsible for product developments for use by both AMS and nuclear utilities. Prior to his CTO role, Mr. Morton served as the AMS Software Development Manager from 1998 to 2016. Also, he is a National Instruments Certified LabVIEW Architect. Mr. Morton has directed many of AMS’ recent technical activities in the area of instrument performance monitoring and online diagnostics. He has been instrumental in the innovation of several technologies at AMS that have led to several patents, journal articles, magazine articles, technical reports, and national publications. He has been the principal investigator for several Department of Energy research projects. Mr. Morton graduated from Tennessee Technological University in 1995 with a Master’s degree in Electrical Engineering. core. Figure 2 shows the principle of the cross-correlation technique. It shows that signals from any two sensors (e.g. a neutron detector and a core exit thermocouple) that are a distance apart can be cross-correlated to calculate the time that it takes for the signal to travel from the first sensor to the second sensor (transit time). This information can then be tracked to identify changes in flow behavior and thereby reveal any flow blockages or flow anomalies. Boiling Water Reactors (BWRs) can also benefit from the noise analysis and cross-correlation technology for a variety of applications such as measurement of vibration of the instrument tube at the center of the core. In fact, researchers at the Oak Ridge National Laboratory (ORNL) and the University of Tennessee (UT) used data from the Browns Ferry Nuclear Power Plant in Alabama to demonstrate the application of the noise analysis technique for diagnosis of vibration issues in BWR plants and to determine void fraction and measure core stability margins in two-phase flow regimes [2]. These technologies can be used not only in existing PWR and BWR plants, but also integrated into the design of new generation of reactors including small modular reactors (SMRs) and advanced nuclear power plants [3]. Operating Experience As nuclear power plants age, embrittlement and fatigue of metallic components and reactor internal support structures can threaten the safety of the plant. In particular, as operational anomalies including excessive vibration, detached components, flow anomalies, and flow blockages can develop within the reactor vessel or primary coolant system as the plant ages. Recent incidents involving baffle bolt failures at the Indian Point and Salem nuclear stations in the United States and similar events in French plants and other reactors are examples of why increased monitoring of reactor vessel internals is critical to safety and sustainability of the aging nuclear fleet [4]. These examples have also revealed that the conventional practice of visual inspection with underwater cameras, ultrasonic testing, and eddy current measurements may not by themselves be sufficient to detect the onset of component failures. Furthermore, most conventional measurements can only be performed during plant outages as described in an article published in the February 2019 issue of Nuclear News magazine on aging management of reactor internals [5]. Adding vibration monitoring using existing neutron detectors would be a passive and very cost effective measure to supplement existing practices and thereby improve the capability to detect incipient failure of reactor internals. Plants in the U.S. and other countries have seen core barrel, thermal shield, and other major components within the reactor vessel become loose, and in a few cases, fall off their support causing major disruptions to plant operation not to mention the very high repair and replacement costs ($5 to $50 million dollars depending on severity of the problem). Furthermore, broken metal parts have been found to block the flow of coolant near fuel rods causing partial meltdown of fuel elements [6]. These problems can easily be avoided by acquisition and analysis of existing sensor signals to provide early warning of structural failures, flow anomalies, and other problems. Also, PWR plants have often suffered from the well-known “Quadrant Power Tilt Alarms” which occur when flow imbalances or flow anomalies cause a portion of the core to experience more fuel burn up and higher temperatures than other portions. Such anomalies give rise to uneven flux profiles and accelerated aging in the affected portion of the core and can be detected using the noise analysis and cross-correlation techniques. Figure 2. Principle of Cross-Correlation Technique. (Continued on page 42) c t s s