Nuclear Reactor Boilers

Nuclear reactor development began during the 1940s, following the demonstration of nuclear fission by Fermi in 1942. Since the 1950s, nuclear boilers have been used increasingly for the generation of electrical power. 

Many dozens of industrialized countries now employ nuclear reactors for power generation, and some countries produce more electrical power by nuclear reaction than by fossil fuel combustion (France is an example). The United States, however, has the largest installed capacity of nuclear-powered boiler plants (in the year 2000 there are more than 120 nuclear reactor power plants in the United States). Nuclear power is also widely used for marine duty in both commercial and naval vessels. 

The heart of the nuclear reactor boiler plant system is the reactor core, in which the nuclear fission process takes place. Nuclear fission is the splitting of a nucleus into two or more separate nuclei. Fission is usually by neutron particle bombardment and is accompanied by the release of a very large amount of energy, plus additional neutrons, other particles, and radioactive material. The generation of new neutrons during fission makes possible a chain reaction process and the subsequent 

The three types of radiation commonly resulting from the decay of specific nuclides are  

There are various types of nuclear power reactors, including boiling water reactors (BWR) and pressurized water reactors (PLWR or LWR), which are both light-water reactor (LWR) designs and are cooled and moderated by water. There also are pressurized heavy-water reactor (PHWR or HWR) designs. 

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There are four fundamental types of boiler available today—electric boilers, fire tube (shell or FT) boilers, water tube (WT) boilers, and nuclear reactor boilers. Electric boilers apart, all other types are essentially developments from shell and tube heat-exchanger designs. 

The first three boiler types may be variously used for commercial, institutional, or industrial applications. Fire tube boilers also may be used for steam turbine generator duty at lower electrical outputs, whereas only WT and nuclear reactor boilers are employed for utility power generation. 

Nuclear reactor boiler plants consist essentially of a central reactor core providing controlled energy that is transferred via a pressurized cooling system to one or more steam generators. These in turn provide superheated steam for delivery to a turbine. 

Principles of Nuclear Reactor Boiler Plant Operation... 

Where condenser in-leakage develops in nuclear reactor boilers, calcium hideout may occur in the reactor water, implying that some leakage of Ca and Mg may have occurred from the condensate polishers. There also may be some sodium or chloride leakage from the polishers (under good conditions, the polisher effluent usually contains below 0.1 ppb Na). 

Metal Cleaning. Citric acid, partially neutralized to - pH 3.5 with ammonia or triethanolamine, is used to clean metal oxides from the water side of steam boilers and nuclear reactors with a two-step single fill operation (104—122). The resulting surface is clean and passivated. This process has a low corrosion rate and is used for both pre-operational mill scale removal and operational cleaning to restore heat-transfer efficiency. 

Steam engines and steam turbines require steam boilers, which, until the advent of the nuclear reactor, were fired by vegetable or fossil fuels. During most of the nineteenth century, coal was the principal fuel, although some oil was used for steam generation late in the century. 

The basic steam cycle for a steam turbine installation is called a Rankine cycle (named after Scottish engineer and physicist William John Macquorn Rankine). This cycle consists of a compression of liquid water, heating and evaporation in the heat source (a steam boiler or nuclear reactor), expansion of the... 

Reactor vessel Reactors produce intense heat, and those employed in large nuclear power boiler installations (typically 800-1,000 MWh) may have 50,000 to 60,000 sq ft of heat transfer surface area with a heat flux of from 150,000 to 500,000 Btu/ft2/hr. 

Figure 2.8 Nuclear reactor, straight tube, steam generating boiler.

To complete the broad picture of what is meant by burn-out, it is useful to consider further the particular burn-out condition which produces tolerable wall temperatures. Such a condition must occur, for example, in any practical, once-through boiler system, where a change from, for example, liquid water at inlet to superheated steam at outlet takes place in a single heated channel. Normal operation of nuclear reactors beyond burn-out has also been contemplated, and Collier et al. (C5) have described successful experiments with irradiated Zircaloy-clad rods operating continuously beyond burn-out... 

The essential ingredients for producing heat in a thermal fission nuclear reactor are the fuel and a moderator. A heat transport system with its coolant is necessary to convey the heat from the reactor to boilers where steam is produced to drive the turbogenerator. The natural materials available for fuel and moderator are uranium ore and water natural uranium extracted from the ore comprises the fissionable isotope uranium-235 and water contains hydrogen which is a good moderator. (Table I)... 

The 1946 prediction of Robert Oppenheimer, one of the pioneers in this field, that great nuclear reactors would be supplying enough energy to heat a large dty within ten years, had practically come true. Altogether there were some twenty-nine reactors operating in the United States, plus three national" reactor laboratories in full production in 1955. In January of that year the first atom-powered transport became a reality when the United States submarine Nautilus put to sea successfully. This boat and its sister ship, the submarine Sea Wolf, built soon after, became the forerunners of atom-powered merchant ships, locomotives, airplanes, and such portable nuclear plants as small house boilers and atomic reactors for medical research. 

The United States, ASME code, is divided into sections which cover unfired vessels, boilers, nuclear reactor vessels, and vessels constructed of fibre-glass-reinforced plastics. A comprehensive review of the ASME code is given by Chuse (1977) and Yokell (1986) see also. Perry et al. (1997). 

It should also be remembered that most evolving technologies, whether boilers during the 19th century, airplanes in this century, or nuclear plants, entail some accidents from which lessons are learned. Both the Three Mile Island accident, from which only limited radioactivity escaped to the environment, and the Chernobyl disaster, have led to the introduction of new safety features in nuclear reactors, in plant operating procedures, and in regulations. 

The boiler serves to transfer heat from a burning fuel (or from a nuclear reactor) to tlie cycle, and tlie condenser transfers heat from the cycle to the surroundings. Neglectingkinetic-and potential-energy changes reduces tlie energy relations, Eqs. (2.31) and (2.32), in either case to ... 

A common thread in many of the reactor technologies that currently exist or that are under development is the use of water as the heat transport medium (the coolant ). In many respects, water is an ideal coolant, because it has a high heat capacity, can be obtained in a high purity, is inexpensive, has a wide liquid range (0-374.15 °C), is easily handled, and had been used since the dawn of steam power. Thus, in their most fundamental form, water-cooled nuclear reactors (WC-NRs) comprise a nuclear boiler, a heat transport system (piping, channels, steam generators, etc.), a set of turbines (high pressure, intermediate pressure, and low... 

A representation of the "energy zones" of a nuclear reactor. Heat produced by the reactor core is carried by water in a second zone to a boiler. Water in the boiler (third zone) is converted to steam, which drives a turbine to convert heat energy to electrical energy. The isolation of these zones from each other allows heat energy transfer without actual physical mixing. This minimizes the transport of radioactive material into the environment. 

Power Production. Steam cycles for generation of electric power use various types of boilers, steam generators, and nuclear reactors operate at subcritical or supercritical pressures and use makeup and often also condensate water purification systems as well as chemical additives for feedwater and boiler-water treatment. These cycles are designed to maximize cycle efficiency and reliability. The fuel distribution of sources installed in the United States from 1990—1995 are as follow coal, 45% combined cycle, 27% miscellaneous, 14% nuclear, 11% solar, oil, and geothermal, 1% each and natural gas, 0.3%. The 1995 summer peak generation in the United States was 620 GW (26). The combined cycle plants are predominantly fired by natural gas. The miscellaneous sources include bagasse, black liquor from paper mills, landfill gas, and refuse (see Fuels frombiomass Fuels fromwaste). 

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