Comment

1 July 2006

Human Element Drives Design

Nuclear power plants modernize for safety

By Joseph Naser

The nuclear industry is facing a dilemma; obsolete equipment, which can lead to plant performance and safety issues in the long run. A logical response is to modernize instrumentation and control (I&C) programs using digital equipment to increase power output capacity, reliability, and availability. As these plants age, and as more plants receive their license renewals, these plants are seeing the benefits of modernizing using digital technology to maintain high levels of safety and increase electricity production more cost effectively. But in today’s nuclear environment, such modernizations must remember the human factor in their initial design to avoid human error down the road.

The Electric Power Research Institute (EPRI) and the U.S. Department of Energy (DOE) are supporting the nuclear industry in their modernization efforts with a jointly funded guidance project to help specify, design, and implement control rooms and human systems interfaces in their infancy. The guidance project will also address operations, personnel training and license activities to support safe operation while also considering human cognitive processing abilities.

The old design of I&C equipment in nuclear power plants in the U.S. included analog and relay components, and in some cases rudimentary digital technology. Today, most of these plants continue to operate with the original I&C equipment, some of which is exceeding its life expectancy and increasing maintenance efforts to sustain acceptable system performance. Replacement parts are not as readily available; manufacturers who support analog technology are dwindling, limiting what manufacturers can add to their plant systems.

The guidance includes 35 sets of guidelines in five areas: 

1. Control room modernization planning
2. Human factors engineering (HFE) design, analysis, and tools
3. Detailed HFE guidelines
4. Regulatory and licensing activities 
5. Special topics related to operations and maintenance

Much of the guidance applies to new plant design, but some utilities, suppliers, and third party integrators have already successfully used sections of the guidelines in their modernizations.

In most cases, manufacturers will modernize their control rooms in increments over several fuel-cycle outages. After each modernizing step, the amount of analog technology will decrease, and digital technology will increase. Likewise, the relationship between humans and control room technology will keep changing until the modernization program is completed. Depending on how far the plant wants to go with its modernization program, the final configuration may still be a combination of analog and digital technology.

Modernization activities cover a broad spectrum, from replacing a few obsolete components with newer digital devices to a fully digital control room and digital I&C system human-system interfaces (HSIs) over several years. The new HSIs are computer-based and may incorporate features such as soft controls, computer-based procedures, touch-screen interfaces, sit-down workstations, and large-screen overview displays. From the guidance in this document, users can support the entire spectrum of plant modernization as well as new plant control room and HSI design.

New digital systems provide the opportunity to give plant staff information they did not have with conventional systems. Improved instrumentation and signal validation techniques can help ensure information is more accurate, precise, and reliable. Data processing techniques and the flexibility of computer-based information pres- entation enable designers to present information in ways better suited to plant staff tasks.

These capabilities also allow better information processing leading to more efficient and cost-effective power production. The result should be more efficient operations and maintenance, leading to improved power plant availability and safety through the avoidance of transients, forced outages, and unnecessary shutdowns. The potential benefits also include increased efficiency and power output as well as reduced operating costs.

Safety important throughout transition

Nuclear plants are concerned about increases in human error during the transition if new digital equipment and the resulting control rooms, and HSIs don’t take into account human factors throughout the transition. A vision of the final configuration of the control room needs to come into play at the beginning of the modernization program. Developers should use current human factors knowledge and guidance during each step in reaching the final configuration. There is also a possibility funding constraints could delay or eliminate future modernization steps, so control room and interfaces at the end of each step should be totally capable of controlling the plant under all conditions and for the rest of the life of the plant.  

Although we have seen publications with numerous human factors guidelines, there has not been specific guidance to satisfy safety requirements and achieve high levels of availability, reliability, and productivity in nuclear power plants. The United States Nuclear Regulatory Commission (NRC) has published human factors guidance documents in some related areas intended for NRC use in reviewing proposed upgrades regarding safety issues. Yet they do not provide additional guidance to specify, design, implement, operate, maintain, and train for cost-effective, integrated HSIs to ensure safety, availability, reliability, and productivity.

Guidance project details

The EPRI and U.S. DOE project began in 2001 to develop guidance for control rooms and digital HSIs, including human performance related issues. The guidance supports meeting safety requirements and the plant’s operational requirements. The guidance also supports improved cost-effective plant and human performance and reduced likelihood of human errors, resulting in improved plant safety, availability, reliability, and cost-effective operation. This project also developed technical bases to help develop, design, and implement guidance in new critical advanced technology areas related to control rooms, such as process automation and computerized operator support systems. Although they developed the guidelines with modernized control rooms in mind, much of the guidance applies to designing new plant digital control rooms.

Guideline development

These guidelines underwent extensive review and input from multiple facets of the nuclear power industry, national and international, including utilities, suppliers, researchers, and regulatory personnel. They differ from other HFE standards and guidance documents for several reasons. First, most HFE documents are oriented toward design of a new control room. These guidelines specifically address the modification and upgrading of existing control rooms. However, most of the guidelines in this document will also support the design of a new control room. Second, most HFE documents are high-level, specifying performance of task analyses, for instance. But they do not provide a specific methodology. The new guidelines provide detailed methodologies utility personnel can use. Third, most documents focus on HSI design, while these guidelines address a broader range of plant modernization considerations from planning to monitoring the modifications once they are in place. Fourth, the structure of the guidelines meets regulatory guidance and expectations. No other document provides guidance that so clearly interprets and defines the regulatory and licensing issues to consider as part of control room modernization.

The introduction discusses HFE and human performance, covers the scope of the guidelines, and identifies the intended users of the guidance, including operators, engineers, maintainers, managers responsible for modernization projects, I&C designers, control system suppliers, and third party implementers. It also provides the relationship of these guidelines to other HFE guidelines and standards.

A significant I&C and HSI modernization project may extend over multiple outages and requires careful planning to succeed. The control room modernization planning guidelines include management considerations, endpoint definition, migration strategy, human factors program planning, and planning for regulatory and licensing activities.

The management considerations include: 

1. The need for planning
2. The objectives of the planning effort
3. Minimum planning activities
4. Levels of I&C and HSI modernization
5. Interaction between I&C and HSI modernization planning
6. Concept of operations
7. Importance of involving operations personnel
8. Consideration of available systems and equipment
9. Scheduling challenges
10. Documentation of the planning effort
11. Human factoring engineering
12. Licensing considerations

A key aspect of planning is to develop a vision that portrays what the utility would like to have for the final control room and HSI functionality and “look and feel.” The endpoint definition guidelines discuss the need to understand potential functionalities and technologies including their pros and cons. They provide guidance to define the endpoint vision. 

Since in most cases, large modernization projects will occur over several outages, it is critical to have a migration plan to assure each interim configuration produced will support human and plant performance during the periods of operation between outages. This migration plan is also needed to ensure achievement of the final endpoint vision. The migration strategy guidelines cover:

1. Planning and evaluating the transitions at each migration step
2. Ensuring adequacy of the interim HSI
3. Conceptual design of the HSI changes 
4. Evaluating the costs and minimizing project risk
5. Licensing evaluations

It is important to develop an HFE program to ensure the integration of HFE into the plant design and modification process will support development, design, evaluation, and modification of HSIs. An important aspect of HFE planning is establishing a methodology for grading the level of HFE effort (i.e., ensuring the level of HFE effort is commensurate with the importance of the modification). The human factors program planning guidelines describe HFE program elements. They also present a graded approach to HFE activities and provide sources of additional HFE information.

It is necessary to establish a licensing plan, including: when and how to interact with the regulatory authority; the scope of the regulatory review; and needed documentation. The planning for regulatory and licensing activities guidelines identify frequently asked questions, planning guidance for licensing activities, and additional sources of information.

The guidelines for HFE design, analysis, and tools begin with guidance on how HFE fits into the overall design process and how to plan the application of HFE for specific modifications. These guidelines describe the HFE activities that contribute to the design process and how to identify which activities are needed for a particular modification. Where appropriate, the guidelines also include the graded approach into three levels of effort for the activity. These guidelines cover:

• Implementing HFE in the design process
• Operating experience review
• Function analysis and allocation
• Task analysis
• Staffing, qualifications, and integrated work design
• Human error analysis
• Human-system interface and procedure design
• HFE verification and validation processes
• In-service monitoring of modifications
• Methods and tools for collecting information from users

The detailed HFE guidelines provide principles for the design of computer-based capabilities. Some of these guidelines include information display, user interface interaction and management, soft control systems, alarm systems, computer-based procedure systems, and computerized operator support systems.

Each of these set of guidelines provides: an introduction that characterizes the key features of the HSI technology; the appropriate HFE guidance organized by that characterization; and design principles and supplemental information that provides further information about the guideline and how to apply it. Each guideline contains a checklist for the guidance and provides additional sources of information for the designer. 

Regulatory and licensing activities are an important part of the modernization program. Up-front planning can help reduce the cost of the activities related to regulatory compliance and can minimize licensing risk. The regulatory and licensing activities guidelines provide guidance on licensing activities specific to the human performance considerations related to I&C, control rooms, and HSI. These guidelines are:

• Regulatory requirements and expectations
• Engineering evaluations related to licensing
• 10 CFR 50.59 evaluations
• Licensing submittals and other NRC interactions
• Roadmap to HFE-related regulatory requirements and guidance

The special topics related to operations and maintenance guidelines cover several of the unique digital I&C and HFE considerations during the operations and maintenance phases. These guidelines are:

• Human factors engineering for the maintenance of digital systems
• Human factors engineering for configuration management
• Training considerations unique to digital I&C upgrades
• Safety monitoring and control in modernized control rooms
• HSIs needed to supplement DCS workstations in a modernized control room
• HFE design considerations for monitoring and control facilities outside the main control room

About the Author

Joseph Naser is an instrumentation and control manager with the Electric Power Research Institute in Palo Alto, Calif. Reported results came from the work of development team and industry working group members John O’Hara with Brookhaven National Laboratory, Bob Fink with CDF Services, Doug Hill with MPR Associates, and Lew Hanes with Halden Reactor Project. The U.S. Department of Energy provided part of the funding for guideline development under the NEPO Program.