Comment

1 July 2006

Control Room Design in the 21st Century

By Dr. Beth Vail

It is approaching 20 years since the industry performed most human factors engineering (HFE) evaluations of commercial nuclear power plant control rooms. The U.S. Nuclear Regulatory Commission (NRC) has updated its design and evaluation process several times to provide a systematic method for evaluating the human system interface (HSI) design for today’s control rooms. The industry is required to use NUREG-0700, Human-System Inter-face Design Review Guidelines, for HSI design submittals prepared by licensees or applicants for a license or new design certification of commercial nuclear power plants. The most recent revision of NUREG-0700 added nearly 500 new guidelines to bring the total guidelines to over 2,000.

In the past, instrumentation and controls (I&C), safety systems, and HSIs were based on either analog, relay, or archaic digital technologies. The computers available during the start of that period were often monoliths that took up large rooms and required submitting batch programs to run jobs. The HSIs, those nuclear power plant parts that personnel interact with in performing their tasks, included pistol-grip control switches, red, green, amber, and white indictor lights, mimic displays, lighted annunciator panels, and hand-written status boards.

Typically, plant and system status came from noisy dot matrix printers and strip chart recorders, along with their messy colored ink pens. Operators often had to acquire data manually and correlate it with other data sources before recording it on a paper data sheet, in an operating procedure, or in a logbook. 

The emergent computer technology has introduced the capability of integrating information from numerous plant systems and supplying needed information to operations personnel in a timely manner. Information integration in the computerized control room can help the operator determine underlying reasons for problems or malfunctions. Other benefits are real-time alarm processing and online presentation and use of operating and accident procedures.

Today, some U.S. nuclear power plants still have their original analog and out-dated digital I&C equipment in operation. Others are in the process of planning control room (and some complete plant-wide) I&C modernization to improve plant reliability, safety, and costs. Numerous versions of the new advanced control rooms are in the regulatory licensing application process. Generation IV nuclear reactors control rooms are in various stages of the design cycle. However, with the introduction of software-based I&C systems for the nuclear power plant control, new safety and HSI integration issues have arisen.

Challenges of the well-integrated computerized control room of the 21st Century include ensuring reduced staffing does not cause increased task complexity, achieving a consistent user interface, ensuring increased automation does not adversely affect the operator’s mental model of the plant, and  systems actually support the operator. 

Human factors engineering

Human factors engineering as a discipline seeks to improve human performance by discovering and applying information about human behavior, skills, capabilities and limitations to the design of devices, tasks, jobs, systems, and environments for productive, effective, and safe human use. Human factors engineering as a process seeks to achieve highly usable equipment and processes.

The HSIs are the parts of a nuclear power plant that personnel interact with in performing their tasks. The major HSIs include displays, controls, alarms, and equipment (and the areas in which these items reside). Benefits of applying good human factors engineering principles to the system or equipment design of the HSI include performance benefits (operator capability to observe and make the required positional maneuvers and movements and to perform the necessary actions), system benefits, and cost benefits.  

New regulations

The NRC reviews the HFE of a nuclear power plant in accordance with its Standard Review Plan, NUREG-0800. You’ll find detailed design review procedures in NUREG-0711, HFE Program Review Model. During the review process, the HSIs undergo evaluation for conformance with the HFE guidelines. NUREG-0700 (Rev. 2) provides the guidelines needed to perform the evaluation.

NUREG-0700 (Rev. 2) was a major reorganization of the Rev.1 document to better align it with the need to address the rapidly evolving technology associated with the HSI. It retained most of the guidelines contained in Rev. 1 of the document. However, the existing guideline numbers did not remain the same, so comparing an HFE analysis performed to Rev. 1 to the new Rev. 2 guidelines becomes difficult. In addition, Rev. 2 added 30% more guidelines and reworded over 100 of the retained guidelines.

Washington Group International has developed a user-friendly automated software tool to enable the user to automatically select the appropriate design guidelines and evaluate the HSI against the selected guidelines.  An extensive technical screening of the NUREG-0700 (Rev. 2) guidelines compared the Rev. 1 guidelines and determined the extent of the change. The modified guidelines were categorized by safety system applicability, level of automation, and the guideline type. The NUREG-0700 (Rev. 2) compliant tool should be available in the second half of 2006.

About the Author

Dr. Beth Vail serves on the ISA-SP18 standards committee, Alarm Management, and ISA-SP101, Human-Machine Interface. She is a consulting engineer at Washington Safety Management Solutions, part of Washington Group International, in Aiken, S.C. Contact her at beth.vail@wsms.com.