James D. White, Oak Ridge National Laboratory (Panel Cochair)
David D. Lanning, MIT (Panel Cochair)
Leo Beltracchi, Nuclear Regulatory Commission
Fred R. Best, Texas A&M University
James R. Easter, Westinghouse
Lester C. Oakes, EPRI
A.L. Sudduth, Duke Power Company
A panel of U.S. specialists conducted a study of instrumentation and controls (I&C) technology used in nuclear power plants in Europe. These findings relate to the countries visited and to pressurized water reactor (PWR) nuclear power plants. The panel visited France, Germany, the Soviet Union, Czechoslovakia, and Norway.
The U.S. is behind in the application of advanced instrumentation and controls in nuclear reactors. All European countries that operate nuclear power plants, as well as Canada, Japan, and the U.S., are moving toward use of digital computers, especially microprocessors, in information and control systems. The operator's role varies by country. Japan and Germany are moving toward a high degree of automation, whereas in France the emphasis is on computer-generated procedures with the decision to enable being made by skilled operators. In U.S. and Soviet plants, the emphasis is on using digital systems to help the operator identify problems, decide on the appropriate corrective actions, and aid in the execution of those actions.
The U.S. is behind in the development and experience of using digital systems in nuclear plants, and in the use of fault diagnosis and signal validation systems. The hardware for digital systems used in all countries comes mostly from U.S. computer companies, but the lack of deployment of digital systems in U.S. nuclear plants has kept the U.S. behind in developing experience in computer system architecture for nuclear I&C systems. The Europeans are also ahead in the use of computer assisted software engineering (CASE) tools and in the development of standards. European instrumentation for nuclear power plants is similar to that in the U.S., although some special instrumentation is being developed.
An advantage to being behind is that the U.S. can learn from the mistakes of those ahead. The digital systems' programmability can entice the user to add complexities that can evolve into problems. Efforts must be made to maintain simplicity.
The panel made a qualitative comparison of the U.S. and Europe in instrumentation and controls for nuclear power plants. Table 28 shows the standing of the countries visited relative to the U.S.
Europe Compared to the United States in Nuclear Power Plant I&C
As shown in Table 28, Europe is ahead of the U.S. and moving ahead further in implementation of products in all seven categories, with the possible exception of instrumentation. In the area of advanced development, Europe is also ahead except for architecture and instrumentation. In basic research, Europe is ahead in four of the seven categories; however, for analog-to-digital transition and for instrumentation, the U.S. is about equal, and the U.S. is ahead in architecture. In other words, U.S. computers are being purchased and utilized in all countries that the panel visited, but the development and implementation of the computers for nuclear power plant instrumentation and control is more advanced in Europe.
There is a move in every country designing nuclear power plants to improve the plant's availability, safety, ease of operation and/or acceptability by the public and regulators. The appropriate balance of automation and manual operation is the subject of considerable debate in the U.S. and Europe today. Most researchers agree that today's technology would support digital automation of all the major systems in a power plant. One of the concerns, however, is how to verify and validate the required software.
In the U.S., the transition from today's nuclear control systems to more automated future designs is likely to occur in phases. One of the purposes of this study was to determine where the European concepts were in terms of evolution of I&C. The U.S. transition may be described in terms of four levels (see Fig. 26). The solid diamonds represent a plant that is operational; empty diamonds represent plants that are not yet operational.
Figure 26. Nuclear Plant I&C State of the Art
In level 1, some of today's analog controllers will be replaced with more reliable digital controllers performing basic proportional-integral-differential (PID) control. This phase of evolution is already under way in the U.S. Generally, digital implementations of control systems on U.S. reactors have been one-for-one replacements of the original analog systems and have not taken full advantage of recent technological developments. As the chart shows, the panel thinks U.S. LWRs are in the beginning of level 1. The French plant Bugey is a little further advanced but also in level 1, while the Japanese Tokyo Electric Power Company's Kashiwazaki-1 and -2 are at the interface with the next level.
Level 2 of the predicted transition will include automation of routine procedures like plant start-up, shut-down, refueling, load changes, and certain emergency response procedures. Significant assistance will be given to the operator through computer-based expert systems and control room displays of plant status. Control will be implemented with digital technology. The newly completed Darlington plant in Canada is at level 2, as are the U.S. Advanced Light Water Reactor (ALWR) and the newest French plant (the N4 class). The German ISAR-II is between levels 2 and 3.
Level 3 is a significant advance toward automation with the operator interacting with and monitoring an intelligent, adaptive supervisory control system. Smart sensors will be expected to validate signals and communicate with fault-tolerant process controllers. Control strategies will be adaptive, and very robust to off-normal conditions. Advanced LMR (PRISM) concepts and MHTGR concepts being studied by the U.S. DOE will have these capabilities. The newest Canadian concept, the CANDU 3, is placed in this category, as is the Japanese Advanced Boiling Water Reactor (ABWR).
Level 4 would be characterized as total automation of the plant, with an intelligent control system aware of operational status and in interactive communication with the operator to keep him apprised of any degraded conditions, likely consequences of these conditions, and possible strategies for minimizing deleterious consequences. At this point most plant functions will be automated and robotized including maintenance and security surveillance.
The control and information system will be an integral part of not only the total plant design, but also the national network of commercial power plants. The control system computer will learn from the network relevant information concerning other plants and component operational experience, and will alert the operator if that experience is relevant to his plant. No U.S. design has gone this far in incorporating advanced technology and automation. The Japanese Frontier Research Group on Artificial Intelligence is working on conceptual definition of a plant of this type. In the evolution of higher levels of automation, the designers will try to improve all aspects of nuclear power plants, including safety and reliability. Progress in all countries should build on successes and experiences in other countries.