US-APWR Human Systems Interface System Verification and Validation Results: Impact on Digital I&C Design

The US-APWR, currently under Design Certification Review by the US Nuclear Regulatory Commission, is a four-loop evolutionary pressurized water reactor with a four-train active safety system by Mitsubishi Heavy Industries. The Instrumentation and Control (I&C) System and Human Systems Interface (HSI) platform applied to the US-APWR is provided by Mitsubishi Electric Corporation. This design is currently being applied to the latest Japanese PWR plant under construction and to the nuclear power plant I&C modernization program in Japan. The US-APWR’s fully digital I&C system and HSI platform utilizes computerized systems, including computer based procedures and alarm prioritization, relying principally on an HSI system with soft controls, console based video display units and a large, heads up, overview display panel. Conventional hard controls are limited to system level manual actions and a Diverse Actuation System. The overall design philosophy of the US-APWR is based on the concept that operator performance will be enhanced through the integration of safety and non-safety display and control systems in a robust digital environment. This philosophy is augmented, for diversity, by the application of independent safety-only soft displays and controls. As with all the advanced designs, the digital systems open as many questions as they answer. To address these new questions, for an eight-week period during the months of July and August 2008, an extensive verification and validation program was completed with the objective of assessing US operators’ performance in this digital design environment. Over this time period, eight operating crews were subjected to a four-day exercise in which seven scenarios were run on Mitsubishi’s dynamic simulator. In all, twenty-two US-licensed operators and senior operators took part in the program. Additionally, a PC verification software package was developed to independently evaluate video display screen designs. Subjective and objective data were collected on each crew for each scenario and an extensive convergent measures analysis was performed, resulting in the identification of both specific design as well as generic conclusions. This paper discusses the USAPWR design, the V&V program data collection and analysis, and the study results related to the ongoing discussion of the impacts of digital systems on human performance, such as workload, navigation, situation awareness, operator training and licensing.