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Plant Operation and Maintenance
Since the 1979 accident at Three Mile Island, all aspects of nuclear power plant operations and operator training have been greatly improved, making Western nuclear plants safer today than ever before.1
Extensive training programs for nuclear plant operators now include simulator training similar to that used in airline pilot training. All nuclear power plant operators must pass a series of psychological, physical and intelligence tests. Utilities test regularly and rigorously and operators go through regular periods of retraining.2
No other industry requires more extensive retraining and retesting of its operators than the nuclear industry.3
Recent operating experience indicates that operator and other personnel errors, inadequate maintenance, and maintenance and surveillance testing errors are all significant contributors to operating events that can lead to severe accidents. These contributors can cause the total loss of one or more safety systems and multiple equipment failures that can substantially erode the defense-in-depth philosophy and lead to accident conditions beyond the design basis of the plant.4
To guarantee safety, employees must perform their tasks with perfect thoroughness, caution, and alertness. It is no more realistic to expect consistently high levels of performance from pipe fitters or electricians than it is to expect it from the ablest licensed operator. And even if training standards were equally rigorous for all power plant workers, humans will still make mistakes.5
A large proportion of accidents happen at night, on weekends, or during start ups after a vacation period. Judgment and alertness may be affected adversely on late shifts, on shifts where morale is likely to be low, or where attention is wandering because of holidays or other reasons.6
In the past, single-unit nuclear power plants operated with less than 100 employees on site. Now, due to the greater number of regulatory requirements and heavier workloads, the minimum reactor work force has increased to 200 or more.7
The overall safety roles of the human operating crew are:
Following the 1979 accident at Three Mile Island (TMI), virtually every country with significant nuclear power programs made major re-evaluations of their operating practices. The main lessons derived from analyses of the TMI accident were the need for:
In the aftermath of TMI, the NRC developed more rigorous requirements for nuclear power plant control room operators and managers. To gain a license, individuals must complete training programs that include classroom, simulator and on-the-job components. Following completion of the training program, candidates for licenses must pass an NRC exam. Annual re-qualification is required, consisting of refresher training and exams.10 Training programs in the U.S. are under the direction of the utilities.11
For many years nuclear plant safety reviews have supported the view that the quality of management is essential to the safety of plant operation. An investigation into the causes of the accident at TMI concluded that "the principal deficiencies in commercial reactor safety today...are management problems...Many nuclear plants are probably operated by management that has failed to make certain that enough properly trained operators and qualified engineers are available...12
As a direct result of TMI, a "Shift Technical Advisor" (STA) position was instituted for each operating shift of all U.S. nuclear power plants. The STA's primary responsibility is to diagnose abnormal events and advise the control room supervisor.13 After TMI, the nuclear industry also recognized the necessity of having two perspectives on plant performance present in the control room staff -- the systems manager role, and the maintenance or equipment operator role.14
Operator error accounts for a significant number of reported abnormal occurrences at nuclear power plants. Operating experience indicates that some errors can be triggered by the failure of instrumentation and control systems to operate reliably and to assist operators in preventing events from occurring that challenge plant safety systems. Still others can be related to faulty or improperly executed operating and maintenance procedures.15
Between 1981 and 1983 the Licensee Event Report (LER) data base contained over 2000 events involving human error.16 Factors such as fatigue, stress, poor training, time constraints, and unclear or inadequate instructions all contributed to operator errors.17
Following the accident at TMI, studies conducted under the auspices of the U.S. Department of Energy indicated that the design, procedures, and operational aspects of testing and maintenance at nuclear plants all needed improvement.18
Testing and maintenance activities are conducted by non-licensed operators and craftspeople, whose activities are not subject to the planning and discipline of control room operators, yet their activities have a high potential for affecting safety. For example, the failure to restore the auxiliary feedwater system to operability after testing contributed to the TMI accident.19
Deficiencies in quality assurance (QA) and quality control (QC) practices have led to costly delays in plant start-up and, in some cases, have contributed to the cancellation of the plant. Research is needed to improve QA-QC practices in the areas of construction quality and evaluating the conditions of nuclear power plants over time.20
History indicates that serious plant events tend to have precursors -- lesser events or problems trends which eventually cause a serious event. If precursors could be identified and acted on, the probability of serious plant events could be reduced. The accident at TMI was a good example of this. Approximately 18 months before the 1979 accident, an event very similar to the one that led to the TMI accident occurred at another power plant. No formal system was in place to identify the safety significance of the event and communicate it.21
Since TMI, two new utility organizations have been established to investigate, analyze, and exchange information about the performance of U.S. nuclear power plants.22
In a March 1987 report to the President, the U.S. Department of Energy called for the establishment of a centralized review process and firm criteria for reviewing the operation, maintenance, and testing procedures of nuclear power plants -- as well as changes in plant designs. The report stated that in some instances the present process adds unnecessary costs to plants, and can actually increase the risks resulting from plant operation.23
1 Atomic Industrial Forum, Inc., "Operator Training at Nuclear Power Plants," December 1986.
4 Commissioner James K. Asselstine, U.S. Nuclear Regulatory Commission, statement before the Subcommittee on Energy Conservation and Power, Committee on Energy and Commerce, op. cit.
5 Curtis and Hogan, op. cit., p. 10.
6 Ibid., p. 108.
7 Stephen M. Hanauer, "The Human Factor in Nuclear Power Plant Safety: Progress Since Three Mile Island." Progress in Nuclear Energy, Vol. 10, 1982, p. 321.
8 Ibid., p. 299.
9 E.L. Zebroski, R.J. Catlin, J.E. Kenton, R.H. Leyse, & K.A. Nilsson, "World Progess in LWR Safety," Nuclear Safety Analysis Center, Electric Power Research Institute, November 1980, p. 1.
10 Hanauer, op. cit., p. 315.
11 Ibid., p. 318.
12 Ibid., p. 323.
13 Ibid., pp. 322-323.
14 James R. Easter, "Engineering Human Factors into the Westinghouse Advanced Control Room," Nuclear Engineering International, Vol. 32., No. 394, May 1987, p. 35.
15 National Academy of Sciences, Revitalizing Nuclear Safety Research, op. cit., pp. 29-31.
16 U.S. Department of Energy, Office of Scientific and Technical Information, William R. Castro, ed., "Human Error in Events Involving Wrong Unit or Wrong Train," Nuclear Safety, Vol. 25, No. 5, Sept.-Oct. 1984, p. 703.
17 Hanauer, op. cit., p. 302.
18 For example, see Hanauer, op. cit.
19 Ibid., p. 342.
20 National Academy of Sciences, Revitalizing Nuclear Safety Research, op. cit., p. 34.
21 Wiliam L. Lavalee, "The Role of Information Management in Nuclear Plant Operating Experience Review," Progress in Nuclear Energy, Vol. 12, No. 3, 1983, p. 247.
22 Zebroski, et al, op. cit., pp. 6-7.
23 U.S. Department of Energy, Energy Security: A Report to the President of the United States, op. cit., p. 194.