January-February 2019 NPJ

Nuclear Plant Journal, January-February 2019 NuclearPlantJournal.com 39 onto a new backplane card. Most of these card types are common across all systems utilizing Westinghouse ARCH including Combustion Engineering plants, allowing for synergies in the fleet-wide spare part program. All printed circuit cards are hot swappable, which protects equipment and personnel. ARCH’s digital PC cards and modern components are expected to be more reliable than their analog counterparts and are based around an industry-standard, industrial safety grade real-time microcontroller that is founded on the Westinghouse Digital Rod Control System. The microcontroller determines coil timing digitally, eliminating the phase shift network and reducing the hardware associated with phase cross detection. With ARCH, the existing -24VDC power supplies are no longer required, and the auctioneering diode assembly is replaced. The microcontroller-based ARCH allows coil timing logic to be moved from the logic cabinet into the power cabinet, eliminating the need for current order surveillance. A simplified, single-fault tolerant control scheme is applied that works in conjunction with the Ovation logic cabinet rod control upgrade to provide motion demands to the ARCH microcontroller via a demand and select signal. The modular approach re-uses existing cabinet wiring so that when ARCH is installed, new hardwired signals from the logic cabinet to the power cabinets are not required. All that is required is a single fiber-optic connection to each new electronic control assembly. The digital communications between the power cabinets and the logic cabinets support remote diagnostics, maintenance and adjustments to the rod control system. Single-point Vulnerabilities Solved ARCH is designed to provide operators with redundant safeguards against control rod drops. The new PC cards allow for replacement of the existing single movable gripper rectifier bridge with three individual bridges to allow for true double hold of the rods. This removes the chance of a single fault on the stationary gripper causing a rod drop or slip as the movable gripper will maintain holding. It also removes the need for the DC hold cabinet and the work necessary to maintain it. With ARCH, control rod drive holding can be maintained on the movable gripper while the stationary gripper is de-energized for online maintenance. Westinghouse Solid State Rod Control System Power Cabinet (Existing Cabinet Left, ARCH Installed Right). (Continued on page 40)