Water moderator

Tritium is produced in heavy-water-moderated reactors and sometimes must be separated isotopicaHy from hydrogen and deuterium for disposal. Ultimately, the tritium could be used as fuel in thermonuclear reactors (see Fusionenergy). Nuclear fusion reactions that involve tritium occur at the lowest known temperatures for such reactions. One possible reaction using deuterium produces neutrons that can be used to react with a lithium blanket to breed more tritium. 

A variant of the HWR is the Eugen reactor developed by Japan. This reactor is heavy water-moderated but lightwater-cooled. It is fueled by mixed uranium—plutonium oxides. 

One was a water-moderated and water-cooled pressurized reactor the other was a Hquid-metal-cooled iatermediate neutron energy reactor. A land-based prototype submafine power plant called Mark I was built and tested at the National Reactor Testing Station. Argonne National Laboratory provided scientific data and Bettis Laboratory of Westinghouse Electric Corp. suppHed engineering expertise. 

The only large-scale use of deuterium in industry is as a moderator, in the form of D2O, for nuclear reactors. Because of its favorable slowing-down properties and its small capture cross section for neutrons, deuterium moderation permits the use of uranium containing the natural abundance of uranium-235, thus avoiding an isotope enrichment step in the preparation of reactor fuel. Heavy water-moderated thermal neutron reactors fueled with uranium-233 and surrounded with a natural thorium blanket offer the prospect of successful fuel breeding, ie, production of greater amounts of (by neutron capture in thorium) than are consumed by nuclear fission in the operation of the reactor. The advantages of heavy water-moderated reactors are difficult to assess. 

Production in Target Elements. Tritium is produced on a large scale by neutron irradiation of Li. The principal U.S. site of production is the Savaimah River plant near Aiken, South Carolina where tritium is produced in large heavy-water moderated, uranium-fueled reactors. The tritium may be produced either as a primary product by placing target elements of Li—A1 alloy in the reactor, or as a secondary product by using Li—A1 elements as an absorber for control of the neutron flux. 

Production in Heavy Water Moderator. A small quantity of tritium is produced through neutron capture by deuterium in the heavy water used as moderator in the reactors. The thermal neutron capture cross section for deuterium is extremely small (about 6 x 10 consequendy the... 

Elevated pressures are required to keep water in the Hquid state. Liquid water cataly2es oxidation so that reactions proceed at relatively lower temperatures than would be required if the same materials were oxidi2ed in open flame combustion. At the same time, water moderates oxidation rates by providing a medium for heat transfer and removing excess heat by evaporation. 

The alumina column was moderated by a constant concentration of water vapor in the carrier gas. As the temperature of the distribution system was increased, less of the water moderator was adsorbed on the surface. As a consequence, the alumina became... 

Chemical Reactivity - Reactivity with Water Moderate reaction with the evolution of heat Reactivity with Common Materials Rapidly absorbs moisture, forming hydrobromic acid. Highly corrosive to most metals, with the evolution of flammable and explosive hydrogen gas Stability During Transport Stable Neutralizing Agents for Acids and Caustics Flush with water and apply powdered limestone, slaked lime, soda ash, or sodium bicarbonate Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

The Canadian Deuterium Uranium reactor fissions with natural uranium, hence, no dependence on national or international fuel enrichment facilities that are needed to enrich uranium to about 3% U-235 to achieve criticality with light water moderation. 

Pressure-tubes allow the separate, low-pressure, heavy-water moderator to act as a backup hesit sink even if there is no water in the fuel channels. Should this fail, the calandria shell ilsdf can contain the debris, with the decay heat being transferred to the water-filled shield tank around the core. Should the severe core damage sequence progress further, the shield tank and the concrete reactor vault significantly delay the challenge to containment. Furthermore, should core melt lead to containment overpressure, the concrete containment wall will leak and reduce the possibility of catastrophic structural failure (Snell, 1990). 

The HFBR at Brookhaven National Laboratory is a heavy water moderated and cooled reactor designed to provide an intense beam of neutrons to the experimental area. In addition using thimbles i oiitaincd within the vessel, it provides isotopic production, neutron activation analysis, ami muiemi irradiations. It began operation in 1965 at a power of 40 MW to be upgraded to 60 MW m 19S2. 

The facilities at Savannah River(j)) consist of five heavy-water-moderated and cooled production reactors, two chemical separations areas as a heavy water extraction plant, several test reactors, reactor fuel and target processing facilities, the Savannah River Laboratory, and many other facilities necessary to support the operations. During the 1960 s, two of the... 

The phrase "nuclear power" covers a number of technologies for producing electric power other than by burning a fossil fuel. Nuclear fission in pressurized water-moderated reactors—light water reactors— represents the enrrent teehnology for nuclear power. Down the line are fast breeder reactors. On the distant horizon is nnclear fusion. 

In addition to water, virtually any organic polar modifier may be used to control solute retention in liquid-solid chromatography. Alcohols, alkyl2aiines, acetonitrile, tetrahydrofuran and ethyl acetate in volumes of less than one percent can be incorporated into nonpolar mobile phases to control adsorbent activity. In general, column efficiency declines for alcohol-moderated eluents cogqpared to water-moderated eluent systems. Many of the problems discussed above for water-moderated eluents are true for organic-moderated eluents as well. 

Redfield, J. A., 1965, CHIC-KIN, A Fortran Program for Intermediate and Fast Transients in a Water Moderated Reactor, USAEC Rep. WAPD TM-479, Westinghouse Electric Corp., Pittsburgh, PA. (5)... 

Area fraction sea water moderate system 5.00 x io-1 - Default... 

Zirconium is used for structural parts in the core of water moderated nuclear reactors to this end Zr has several good properties and especially it has low thermal neutron cross-section. Hf, on the contrary, has a high thermal neutron absorption coefficient, so it is necessary to be able to prepare Hf-free zirconium. On the other hand, in some cases the Hf properties too may be useful in nuclear technology, in the control rods of submarine reactors. 

Hatcher, S.R., Banerjee, S, Lane, A.D, Tamm, H., Veeder,J.I. "Thorium Cycle in Heavy Water Moderated Pressure Tube (CANDU) Reactors" American Nuclear Society Meeting, San Francisco AECL-5398, 1975... 

Critoph, E. "The Thorium Fuel Cycle in Water-Moderated Reactor Systems" Paper IAEA-CN-36/177 at the IAEA International Conference on Nuclear Power and its Fuel Cycle, Salzburg. AECL-2705, 1977... 

White or yellowish orthorhombic crystal hygroscopic density 1.90 g/cm melts at 399°C vaporizes at 482°C sublimes in vacuum (at 2 torr) at 300°C highly soluble in water moderately soluble in alcohol, ether and pyridine insoluble in benzene, choroform, acetone and ammonia. 

White or yellowish crystalline solid deliquescent melts at 60°C decomposes on further heating very soluble in water, moderately soluble in alcohol. 

White crystal, powder or flake highly hygroscopic the compound and its solutions absorb moisture from the air at various rates depending on calcium chloride concentrations, relative humidity and vapor pressure of water in the air, temperature, surface area of exposed material, and the rate of air circulation at 40% and 95% relative humidity and 25°C, one gram anhydrous calcium chloride may absorb about 1.4 g and 17 g water, respectively. (Shearer, W. L. 1978. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., vol. 4, pp. 432-6. New York Wiley Interscience) density 2.15, 2.24, 1.85, 1.83 and 1.71 g/cm for the anhydrous salt and its mono-, di-, tetra- and hexahy-drates, respectively anhydrous salts melts at 772°C, while the mono-, di-, tetra- and hexahydrates decompose at 260°, 175°, 45.5° and 30°C, respectively the anhydrous salt vaporizes at 1,935°C highly soluble in water, moderate to high solubility in alcohol. 

The pentahydrate is large blue trichnic crystal or light-blue amorphous powder refractive index 1.514 density 2.28 g/cm loses water on heating—two molecules at 30°C, becomes a monohydrate at 110°C and anhydrous at 250°C very soluble in water moderately soluble in methanol slightly soluble in ethanol. 

Anhydrous magnesium sulfate is a white crystalline sohd occurring in alpha form as orthorhomic crystals or as a heta form having triclinic structure density 1.507 and 1.502 g/cm for alpha- and heta-forms, respectively decomposes at 323°C very soluble in water moderately soluble in methanol (5.25g/100 mL at 15°C). 

Colorless cubic crystals or white granular powder deliquescent density 1.52 g/cm3 melts at 634.5°C readily dissolves in water, 50 g/lOOmL at 20°C, 100 g/lOOmL in boiling water moderately soluble in methanol 4.9 g/lOOmL at 20°C soluble in glycerol. 

Anhydrous salt is a colorless crystalline solid density 1.528 g/cm melts at 324°C very soluble in water moderately soluble in ethanol. 

It dissolves with difficulty in water, moderately well in chloroform and benzene, and readily in hot alcohol. Its ignition temperature is 160°C. 

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