Nuclear power plants safety factors

Woods, D. D., Wise, J. A., Hanes, L. F. (1981). An Evaluation of Nuclear Power Plant Safety Parameter Display Systems. In Proceedings of Human Factors Society 25th Annual Meeting. Santa Monica, CA Human Factors Society, Inc. 

Overall assessment of nuclear power plant safety, with account taken of the results of the review of individual safety factors, including agreed corrective actions and/or safety improvements. 

Radionuclides are released to the containment as gases and as aerosol particles by a variety of processes during severe accidents. Modem, mechanistic analyses of these radionuclide releases and the subsequent behaviour of aerosols and vapours under reactor accident conditions strive to be realistic. This realistic approach contrasts with the deliberate attempt to be conservative (which may not have been successful) in the definition of radionuclide behaviour for the design of nuclear power plant safety systems. A discussion of the various radionuclide release processes during severe reactor accidents is presented in Chapter II. Of primary interest in these discussions of release is the potential magnitude of radionuclide release and the radionuclides of most concern. Factors that most affect radionuclide release but can also be affected by accident management measures are discussed. 

The frequency of fire-induced core melt, calculated by averaging the observed frequency of the Browns Ferry type of fire over the experience of U.S. commercial nuclear power plants, was found to be lE-5 per reactor-year, or about 20% of the total core-melt probability e.slimated in the Reactor Safety Study. Kazarians and Apostolakis (1978) performed the same type of calculations under different assumptions and concluded that the frequency of core melt could be higher by a factor of 10. 

Determination of Reliability Characteristic Factors in the Nuclear Power Plant Biblis B, Gesellschaft fur Reaktorsicherheit mbH Nuclear Failure rates with upper and lower bounds and maintenance data for 17,000 components from 37 safety systems Data for pumps, valves, and electrical positioning devices, electric motors and drives from an operating power plant 66. 

There have been two major accidents (Three Mile Island in the United States and Chernobyl in the former Soviet Union) in which control was lost in nuclear power plants, with subsequent rapid increases in fission rates that resulted in steam explosions and releases of radioactivity. The protective shield of reinforced concrete, which surrounded the Three Mile Island Reactor, prevented release of any radioactivity into the environment. In the Russian accident there had been no containment shield, and, when the steam explosion occurred, fission products plus uranium were released to the environment—in the immediate vicinity and then carried over the Northern Hemisphere, in particular over large areas of Eastern Europe. Much was learned from these accidents and the new generations of reactors are being built to be passive safe. In such passive reactors, when the power level increases toward an unsafe level, the reactor turns off automatically to prevent the high-energy release that would cause the explosive release of radioactivity. Such a design is assumed to remove a major factor of safety concern in reactor operation, see also Bohr, Niels Fermi, Enrico AIan-HATTAN Project Plutonium Radioactivity Uranium. 

This paper presents the results of research and development on floating nuclear power plant (FNPP) for electricity and heat production for remote locations and small island or coastal communities. Evaluations of construction period, social and economic factors as well as safety and operational issues of the non-self-propelled barge-mounted NPP is given. 

The U.S. team has established end points defining the successful completion of projects in each technical area. A project reaches its end point when the host country, its nuclear support organizations, and its nuclear power plants can sustain safety achievements and build upon them to meet international nuclear safety practices. These end points are measurable, achievable targets. The U.S. team defmed the end points by weighing several factors for each project its safety impact, its cost-effectiveness, the time needed to achieve results, and the ability of the host country to sustain the safety achievements over a long period. 

Sourced from Draft lEC 300-3-8 (Dependability Management), DEF STAN 00-56 Iss 2 Part 2 Table 4 and ACJ25.1309. This guidance was subsequently removed in DEF STAN 00-56 Iss3 and AMC25.1309. Examples obtained from Qemens, P.L. Human Factors and Operator Errors, J.E. Jacobs presentation second edition, Feb 2002. Human error probabilities are also contained in WASH-1400 (NUREG-75/014) Reactor Safety Study—An Assessment of Accident Risks in U.S. Commercial Nuclear Power Plants, 1975. 

An accident at a nuclear power plant can be caused by many combinations of anomalous initiating event, malfunction and human error. The types of possible accidental situations are studied in the specific safety analysis of each plant and the safety systems described above are designed to prevent, or mitigate the effects of all the accidents chosen as DBAs. Table 3-1 provides an approximate indication of the effectiveness of various safety systems in limiting external releases in a typical loss of coolant accident (the break of a large primary circuit pipe). The figures are for the release of iodine-131 (often assumed as the reference isotope in indicative evaluations of source terms and for a 1000 MWe reactor). As can be seen, the reduction of the releases caused by the safety systems is very significant and corresponds to a factor of the order of one million. 

Since early nineties of the last century, PSA methods have been used as a complementary approach to common deterministic analyses within the process of ensuring acceptable level of nuclear power plant operation safety in Czech Republic. More recently, PSA concept has become a fi eestanding decision-making tool for controlling both instantaneous and permanent plant risk level. Since human factor has been playing a fairly significant role in plant risk profile, special HRA methods had to be adopted as a part of worldwide know-how transfer and used to address human related specifics of Czech NPPs operation, in order to keep the corresponding PSA models as realistic as possible. 

Craig Reiersen (1999), Regulating Organisational Change on Nuclear Licensed Sites and at Corporate Headquarters, a presentation to the Organisation for Economic Co-operation and Development Committee on the Safety of Nuclear Installations May 1999 Workshop Nuclear Power Plant Transition from Operation into Decommissioning—Organisational and Human Factors Considerations. 

The 14 PSR safety factors selected apply to all the facilities on the plant site, including radioactive waste management facilities (see para. 3.1), and are considered sufficient for a comprehensive review of safety. However, the set of safety factors may vary according to the specific needs of the State and the particular nuclear power plant under consideration, and they should be agreed upon before the PSR is initiated. In this connection, PSR experience from nuclear power plants of the same design should be taken into account in the choice of safety factors. 

Major organizational accidents such as the destruction of the space shuttle Challenger in 1986, the explosion of the Chemobyl s nuclear power plant in 1987, the accident with off-shore platform Piper Alpha in 1988 or the destmction of the space shuttle Columbia in 2003, highlighted the relevance of hmnan contributions to organizational safety. Investigations traditionally considered technical and human factors in the development and prevention of these negative events but, in spite of such operational perspective, statistics have revealed the preponderance of human factors in up to 60-70 percent of the situations (e.g., Deldcer, 2002). 

FTA is a tool employed in the analysis of complex systems to estimate the likelihood of a hazardous event. It has been applied, for example, in safety evaluations of nuclear power plants, space missions, air, rail, highway, marine and pipeline transport, liquefied natur gas, chemical manufacturing, and other hazardous material facilities. With this method, all material, personnel, and environmental factors of a complex system can be systematically presented. A well-constructed fault tree enables us to discover failure combinations that would not normally be discovered and provides for both qualitative and quantitative evaluation. 

Human factors are significant in many of the operational events at operating nuclear power plants. For example, for about 6 to 7 yeeirs, human factors have been implicated in 70 to 80% of the French events classified "significant for safety. From 1988, the number of significant events is about constant 6 to 8 significant events/unit/year (in 1986-1987 it was from 10 to 12), furthermore 27% of these events are consecutive to a defect of communication). 

Browzin, B. S. Statistical safety factor concept for determining the probable maximum flood. Specialty Conference on Structural Design of Nuclear Power Plant Facilities, Chicago, IL, December 1973 Proceedings (Publ. ASCE), Vol. n, pp. 557 570. 

Those of us lucky enough to live in wealthy countries are justly proud of our recent environmental progress, which qualifies as self-actualization. But in poorer countries, people are less inclined to care about long-term dangers of pollution. After the nuclear accident at Chernobyl, the power plant ran for 14 more years because the Soviet Union (and then Ukraine) needed electric power and decided that it was too expensive to build a new plant. After 1986, the old plant was staffed by workers who lived in towns where the ambient radiation exceeded the safety threshold by a factor of nine. Despite a second accident in 1991, and despite daily reminders of the dangers radiation, the workers stayed on because they needed jobs and couldn t find other work. Without incentives from the European Community, the Chernobyl nuclear power plant might still be running today. 

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