Nuclear power processes

Eddy-current non-destructive evaluation is widely used in the aerospace and nuclear power industries for the detection and characterisation of defects in metal components. The ability to predict the probe response to various types of defect is highly valuable since it enables the influence of particular parameters to be studied without recourse to costly and time consuming experiments. The solution of forward problems is also essential in the process of inverting experimental data. 

One of the most significant sources of change in isotope ratios is caused by the small mass differences between isotopes and their effects on the physical properties of elements and compounds. For example, ordinary water (mostly Ej O) has a lower density, lower boiling point, and higher vapor pressure than does heavy water (mostly H2 0). Other major changes can occur through exchange processes. Such physical and kinetic differences lead to natural local fractionation of isotopes. Artificial fractionation (enrichment or depletion) of uranium isotopes is the basis for construction of atomic bombs, nuclear power reactors, and depleted uranium weapons. 

Uranium hexafluoride is used in the gaseous diffusion process for the separation and enrichment of uranium-235, which exists in low concentration in natural uranium. The enriched UF is converted back into an oxide and used as fuel for the nuclear power industry. 

Chemical-Process Vessels. Explosion-bonded products are used in the manufacture of process equipment for the chemical, petrochemical, and petroleum industries where the corrosion resistance of an expensive metal is combined with the strength and economy of another metal. AppHcations include explosion cladding of titanium tubesheet to Monel, hot fabrication of an explosion clad to form an elbow for pipes in nuclear power plants, and explosion cladding titanium and steel for use in a vessel intended for terephthaHc acid manufacture. 

Nuclear Applications. Powder metallurgy is used in the fabrication of fuel elements as well as control, shielding, moderator, and other components of nuclear-power reactors (63) (see Nuclearreactors). The materials for fuel, moderator, and control parts of a reactor are thermodynamically unstable if heated to melting temperatures. These same materials are stable under P/M process conditions. It is possible, for example, to incorporate uranium or ceramic compounds in a metallic matrix, or to produce parts that are similar in the size and shape desired without effecting drastic changes in either the stmcture or surface conditions. OnlyHttle post-sintering treatment is necessary. 

Nuclear power has achieved an excellent safety record. Exceptions are the accidents at Three Mile Island in 1979 and at Chernobyl in 1986. In the United States, safety can be attributed in part to the strict regulation provided by the Nuclear Regulatory Commission, which reviews proposed reactor designs, processes appHcations forUcenses to constmct and operate plants, and provides surveillance of all safety-related activities of a utiUty. The utiUties seek continued improvement in capabiUty, use procedures extensively, and analy2e any plant incidents for their root causes. Similar programs intended to ensure reactor safety are in place in other countries. 

If possible comparisons are focused on energy systems, nuclear power safety is also estimated to be superior to all electricity generation methods except for natural gas (30). Figure 3 is a plot of that comparison in terms of estimated total deaths to workers and the pubHc and includes deaths associated with secondary processes in the entire fuel cycle. The poorer safety record of the alternatives to nuclear power can be attributed to fataUties in transportation, where comparatively enormous amounts of fossil fuel transport are involved. Continuous or daily refueling of fossil fuel plants is required as compared to refueling a nuclear plant from a few tmckloads only once over a period of one to two years. This disadvantage appHes to solar and wind as well because of the necessary assumption that their backup power in periods of no or Httie wind or sun is from fossil-fuel generation. Now death or serious injury has resulted from radiation exposure from commercial nuclear power plants in the United States (31). 

Atomic- Vapor Laser Isotope-Separation. Although the technology has been around since the 1970s, laser isotope separation has only recently matured to the point of industrialization. In particular, laser isotope separation for the production of fuel and moderators for nuclear power generation is on the threshold of pilot-plant demonstrations in several countries. In the atomic vapor laser isotope-separation (AVLIS) process, vibrationaHy cooled U metal atoms are selectively ionized by means of a high power (1—2 kW) tunable copper vapor or dye laser operated at high (kHz) repetition rates (51,59,60). 

The largest consumers of water in the United States are thermal power plants (eg, steam and nuclear power plants) and the iron and steel, pulp and paper, petroleum refining, and food-processing industries. They consume >60% of the total industrial water requirements (see also Power generation Wastes, industrial). 

Zirconium is used as a containment material for the uranium oxide fuel pellets in nuclear power reactors (see Nuclearreactors). Zirconium is particularly usehil for this appHcation because of its ready availabiUty, good ductiUty, resistance to radiation damage, low thermal-neutron absorption cross section 18 x 10 ° ra (0.18 bams), and excellent corrosion resistance in pressurized hot water up to 350°C. Zirconium is used as an alloy strengthening agent in aluminum and magnesium, and as the burning component in flash bulbs. It is employed as a corrosion-resistant metal in the chemical process industry, and as pressure-vessel material of constmction in the ASME Boiler and Pressure Vessel Codes. 

A number of special processes have been developed for difficult separations, such as the separation of the stable isotopes of uranium and those of other elements (see Nuclear reactors Uraniumand uranium compounds). Two of these processes, gaseous diffusion and gas centrifugation, are used by several nations on a multibillion doUar scale to separate partially the uranium isotopes and to produce a much more valuable fuel for nuclear power reactors. Because separation in these special processes depends upon the different rates of diffusion of the components, the processes are often referred to collectively as diffusion separation methods. There is also a thermal diffusion process used on a modest scale for the separation of heflum-group gases (qv) and on a laboratory scale for the separation of various other materials. Thermal diffusion is not discussed herein. 

Process Water Purification Boiler feed water is a major process apphcation of RO. Sealants and colloids are particularly well rejected by membranes, and TDS is reduced to a level that makes ion exchange or continuous deionization for the residual ions very economic. Even the extremely high quahty water required for nuclear power plants can be made from seawater. The iiltra-high quahty water required for production of electronic microcircuits is usually processed starting with two RO systems operating in series, followeci by many other steps. 

There are hundreds of types of greases available, and machineiy manufacturers usually provide a guidehne for the greases to be used on their equipment. There are also highly specialized greases, such as the ones that can be used in food processing machineiy, or the ones used in nuclear power stations. 

Hazards and Operability (HAZOP) analysis is an accident detection and prevention technique used primarily by the chemical process industry (CPI) (Lees, 1980). Even though the CPI operates in a different regulatory environment from the commercial nuclear power industry, the goals of risk reduction while maintaining productivity are similar. 

Humans control all chemical and nuclear processes, and to some extent all accidents result from human error, if not directly in the accident then in the process design and in the process inadequate design to prevent human error. Some automatic systems such used in nuclear power reactors because the response time required is too short for human decisions. Even in these, human error can contribute to failure by inhibiting the systems. 

This chapter overviews the techniques for incorporating external events into a PSA. The discussion was primarily aimed at nuclear power plants but is equally applicable to chemical process plants. The types of external events discussed were earthquakes, fires and floods. Notably absent were severe winds and tornados. Tornados are analyzed as missiles impacting the structures and causing common-cause failures of systems (EPRINP-768). Missile propagation and the resulting damage is a specialized subject usually solved with computer codes. 

Given the damage states, the analysis flows much as shown in Figure 6.3-1, depending on the process. For a nuclear power plant, thermal-hydraulic analyses determine the spatial temperature of the damaged core, and consequently the ability of the core to retain radioactive materials. Analysis of the physical processes reveals the amounts of hazardous materials that may be released. 

Nuclear power reactors cause the transmutation of chemicals (uranium and plutonium) to fission products using neutrons as the catalyst to produce heat. Fossil furnaces use the chemical reaction of carbon and oxygen to produce CO2 and other wastes to produce heat. There is only one reaction and one purpose for nuclear power reactors there is one reaction but many puiposes for fossil-burning furnaces there are myriad chemical processes and purposes. 

This chapter shows that chemical process systems may fail and have serious consequences to the workers, public and the environment. Comparing with Chapter 6, chemical processes are similar to the processes in a nuclear power plant, hence, they may be analyzed similarly because both consist of tanks, pipes heat exchangers, and sources of heat. As an example of analysis, we analyze a storage tank rupture. 

If the containment holds, nuclear power plants present no risk to the public. Overpressurization of the containment is the failure mode that could allow direct release of radioactivity to the public. Design a risk reduction investigation of the benefits of releasing the gas pressure through an offgas processing system that removes the particulates. 

A leader in applying PSA to other parts of the chemical process industry has been the AlChf. s Center for Chemical Process Safety. A major difference between PSA for nuclear power and PSA for chemical processing has been the lack of government regulations that require risk analysis for chemical processes. A primary impetuous has been the Occupational Safety and Health Administration s (OSHA) PSM rule that defines the application of PSA to the chemical industry for ihc proteciion of the public and workers. In addition, the Environmental Protection Agcrii, . (EPA) regulates waste disposal. 

I am a physicist who switched to nuclear engineering for my Ph D. My introduction to PSA was as an original participant in the Reactor Safety Study in 1972. Material for this book was first gathered in 1974 for a workshop on what to expect in WASH-1400 (the results of the Reactor Safety Study). Materials were gathered over the years for EPRI, Savannah River Laboratory, and other workshops. A culmination was in 1988 with "Probabilistic Risk Assessment in the Nuclear Power Industry" with Robert Hall as coauthor. This book updates these materials and adds material on PSA in the chemical process industry. I prepared the material for printing using a word processor... 

This incident occun ed in a nuclear power station but could just as easily occur in the process industries. 

According to a recent report [11], the nuclear power plant was the focus of the designers attention the standards used for the nuclear power plant were more stringent than those for the rest of the submarine. In the process industries utilities, storage areas and offplots often get less attention than the main units and are involved in disproportionately more incidents. 

The cognitive approach has had a major influence in recent years on how human error is treated in systems such as chemical process plants and nuclear power generation. In the next section we shall describe some of the key concepts that have emerged from this work, and how they apply to the analysis of error in the CPI. Discussion of the cognitive view of human performance are contained in Reason (1990), Hollnagel (1993), Kantowitz and Fujita (1990), Hollnagel and Woods (1983), and Woods and Roth (1990). 

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