Water-Cooled Reactors

The thermal efficiency (rj) of a nuclear power plant is defined by the ratio rate of electrical energy output 

The unit of energy in both cases is the megawatt. The abbreviations MWe and M Wt are used where it is necessary to distinguish between electrical and thermal power output. 

For the simplest type of coolant cycle, the reversible Carnot cycle, the thermodynamic efficiency is defined by the relation 

Since there is little flexibility in the choice of Tr, which is set by the characteristics of the external water supply for the condenser, the achievement of a high thermal efficiency makes it necessary to operate with steam at the highest practicable temperature. This in turn means that the primary coolant should also be at a high temperature. In order to prevent boiling at this temperature, the primary circuit must be run at a pressure well above the saturation pressure of water at the temperature of the coolant. The most basic limitation on the primary coolant temperature is set by the condition that the fuel pins must remain at a temperature below that at which damage might occur to the cladding or the fuel itself. In practice, in a water-cooled 

A typical heat exchanger, or steam generator, for a PWR is illustrated in Fig. 6.16. The generator is divided into a lower and an upper section, known as the evaporator and the steam drum. The former consists of a U-tube heat exchanger and the latter houses moisture-separating equipment. Each of the U tubes is welded to a tubesheet the space under the tubesheet is divided in two by a vertical divider plate which separates the inlet from the outlet flow. The high-temperature primary coolant enters by the primary inlet, flows through the U tubes, and leaves by the primary outlet. 

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Note that the only other plutonium production site in the U.S. was at Richland, Wa.shington where graphite-reflected light water cooled reactors were used. 

Using a homogeneous model proposed by Owens (1961) for low void fractions (a < 0.30) and high mass flux, as is usually encountered in a water-cooled reactor, the momentum change (or acceleration) pressure gradient term is obtained from... 

Vessel blowdown. The previously mentioned relationships for the critical flow rate of a steam-water mixture can be employed with the conservation of mass and energy for a vessel of fixed volume to determine its time-dependent blowdown properties. The range of problems associated with coolant decompression in water-cooled reactors is quite broad. The types of hypothetical (some are even incredible) reactor accidents may be... 

Coolant property (D20 and HzO) effects on CHF. Fluid property effects here refer to fluids of heavy water versus light water as used in water-cooled reactors. For other fluids, readers are referred to Section 5.3.4. These effects were taken... 

Borgartz, B. O., T. P O Brien, N. J. M. Rees, and A. V. Smith, 1969, Experimental Studies of Water Decompression through Simple Pipe Systems, CREST Specialist Meeting on Depressurization Effects in Water-Cooled Reactors, Bettelle Institute, Frankfurt, FRG. (3)... 

Mass Transport at Very Low Concentrations. Reactor Circuits. Early in the development of water-cooled reactors, it became apparent that at temperatures of 250-300 C with a non-isothermal circuit, corrosion of carbon steel could lead to significant mass transport of iron if the chemistry of the system were not properly controlled. The resulting buildup of large deposits of crud" on fuel surfaces caused fuel failure. However, the large cost differential between carbon steel and stainless steel provided an incentive to identify chemistry conditions for the successful use of carbon steel. 

After a few years of operation there was a significant increase in radiation fields from the primary circuit piping in the Douglas Point generating station. Other water-cooled reactors around the world experienced similar effects. The principal source of the radioactivity was traced to cobalt-60, formed by neutron absorption in the natural cobalt-59 which arose from hard-facing alloys and was also present as an impurity in boiler materials such as HMDnel, and in carbon steel and other structural materials. The mechanism of this radioactivity transport was found to be corrosion of the cobalt bearing materials, transport... 

Oka, Y. Physics of supercritical-pressure light water cooled reactors. Proc. 1998 Frederic Joliot Summer School in Reactor Physics, Caderache, France, and references cited herein, 1998 240-259 pp. 

NuStart made its start in September 2005 with the selection of two potential sites for new reactors Grand Gulf, located near Port Gibson, Mississippi and owned by a subsidiary of Entergy and Bellefont, located near Scottsboro, Alabama and owned by the TVA. Rather than using pebble-bed technology, NuStart is promoting the use of water-cooled reactors. Its next step is to seek COLs for the sites from the NRC. 

To monitor radioiodine species in gaseous effluent from water-cooled reactors, a four-component iodine sampler was used (Voilleque, 1979), designed to separate iodine species as follows ... 

Reaction is first order in gas reactant. 3. Gas and liquid stream are in plug flow. 4. Reactor is isothermal. 5. Gaseous reactant concentration in the gas phase is constant throughout the reactor. 6. A fraction of the catalyst external surface (tice) is covered by a flowing liquid film while the rest is exposed to a thin stagnant liquid film. Assumption 2 was verified by already reported kinetic studies. A water cooled reactor with low feed concentrations of a-methylstyrene operated between 15°C and 20°C satisfies assumptions 1 and 4 due to low volatility of the liquid reactant and due to small overall heat effects, respectively. 

Cline JA, Jonah CD, Bartels DM (2000) In The solvated electron in supercritical water spectra, yields, and reactions, Proceedings of the 1st International Symposium in Supercritical Water-cooled Reactors, Design, and Technology, Tokyo, Nov 6-9... 

Li-7 1. Water-cooled reactors use lithium-7 hydroxide as a water conditioner 2. Possible coolant in LMFBR... 

The United States derived about 20 percent of its electricity from nuclear energy in 2002 (EIA, Electric Power Monthly, 2003). The 103 power reactors operating today have a total capacity of nearly 100 gigawatts electric (GWe) and constitute about 13 percent of the installed U.S. electric generation capacity. The current U.S. plants use water as the coolant and neutron moderator (hence called light-water reactors, or LWRs) and rely on the steam Rankine cycle as the thermal-to-electrical power conversion cycle. Other countries use other technologies—notably C02-cooled reactors in the United Kingdom and heavy-water-cooled reactors (HWRs) in Canada and India. 

In compliance with the closed fuel cycle concept accepted in Russia, SNF imloaded from Nuclear Submarines (NSs) with water-cooled reactors (WER) as well as SNF of nuclear icebreakers are forwarded to PA Mayak for reprocessing, fuel of liquid-metal coolant reactors, zirconimn-cladding fuel and damaged Spent Fuel... 

The main advantage of UC is the high thermal conductivity. On the other hand, the low chemical resistance is a major disadvantage UC is decomposed by water below 100 °C, which is prohibitive for its use in water-cooled reactors. However, UC may be applied in gas-cooled reactors or in the form of UC/PuC mixtures in fast sodium-cooled breeder reactors. 

The intense primary y radiation due to nuclear fission, the secondary y radiation emitted by the fission and activation products and the radiation from the fission products give rise to radiation-induced chemical reactions. The most important reaction is the radiation decomposition of water in water-cooled reactors, leading to the formation of H2, H2O2 and O2. Many substances dissolved in the water influence the formation of H2 (Fig. 11.18). In most closed coolant systems equipment for... 

Figure 11.18. Influence of various components on the formation of hydrogen by radiolysis. (According to J. K. Dawson, R. G. Sowden Chemical Aspects of Nuclear Reactors. Vol. 2. Water-Cooled Reactors. Butterworths. London 1963.)...

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