As the nuclear fleet ages, Westinghouse- and Combustion Engineering (CE)-designed plants are experiencing a greater number of Control Rod Drive Mechanism (CRDM)- and Control Element Drive Mechanism (CEDM)-related issues. These issues can range from improper polarity between coils; failed splices within coils; past operation of coils at excessive temperatures or current causing turn-to-turn shorts; cable and connector degradation; latch assembly wear; crud induced mis-stepping ; and failed latch assembly springs .
These problems can be exacerbated by the fact that it is difficult to diagnose electro-mechanical issues prior to reactor disassembly. Since there are currently no predictive monitoring services which can be deployed to anticipate issues in advance of experiencing malfunctions plants can experience costly unplanned downtime.
Currently, coil current traces are only recorded during stepping of the control rods during plant startup, and potentially when the plant is operating, if allowed by plant procedures. The traces are reviewed and can be transmitted to Westinghouse for analysis and diagnosis. As such, there is limited real-time feedback and limited ability to perform additional diagnostics.
As the Original Equipment Designer and Manufacturer of both Westinghouse CRDMs and Combustion Engineering CEDMs, Westinghouse has extensive experience designing, testing and troubleshooting Control Drive Mechanisms (CDMs.) This experience and extensive knowledge base has been utilized to develop our CDM Diagnostic Test System.
CDM Diagnostics Test System Connection
In order to address the above issues, Westinghouse has developed a single automated system and service for the diagnostics of latch assemblies and coil stacks. The system enables all tests to be performed on the CDM system with the plant offline and offers the flexibility to perform these tests at various plant configuration stages in an outage.
Westinghouse’s CDM Diagnostic Test System and service has the ability to energize the coils, activate the CDM gripper components, and record various current/voltage response data while the plant is offline for a scheduled outage. This can be accomplished by connecting the test system to the output fuse locations of the rod control cabinet either prior to disconnecting or following reconnection of the cables from the reactor vessel head to the rod control system. This enables the validation of the entire conductor path (including cables and connectors). Alternatively, this test can be run to isolate just the CDM via a direct connection to the coil stack connector while the reactor head is in the stand.
The CDM Diagnostic Test System automatically reduces and analyzes the recorded data to find faults. The data can be trended after several screenings to predict future hardware issues as a preventative measure when a utility reports misstepping or other CDM-related actuation issues. Over time, the use of this diagnostic system will enable plants to monitor equipment health, anticipate potential issues ahead of failure, and enable tracking and trending of data.
CDM Diagnostics Software Interface
The Westinghouse CDM Diagnostic Test System offers an all-in-one tool (and service) to perform:
CDM Diagnostics Test System
Westinghouse is currently offering a service to perform the diagnostics testing and data review and analysis. This service can be coupled with longer term data trending and predictive analysis support, during which Westinghouse will work with utilities to identify future areas of focus for and improvement.