Heavy elements water reactors

M10. Matzner, B., Experimental performance evaluation of proposed fuel elements for the steam generating heavy water reactor, NOR-1643, Columbia Univ. (1964). 

HELP HEU HFO HFR HLW HREE HRL HT HTGR HWR Hydrological evaluation of landfill performance Highly enriched uranium Hydrous ferrous oxide or ferric hydroxide Hot fractured-rock High-level nuclear waste Heavy rare earth elements (Gd-Lu) Hard rock laboratory High temperature High-temperature gas-cooled reactor Heavy water reactor... 

The total amount of plutonium formed in various reactors is givoi in Table 21.4. The old gas-graphite reactors and heavy water reactors are the best thermal plutonium producers. They have therefore been used in weapons fabrication. The fast breeder reactor is also an efficient Pu producer. Whereas thermal reactors (except at very low bumup) produce a mixture of odd and ev i A Pu isotopes, a fast breeder loaded with such a mixture, by a combination of fission and n-capture increases the relative concentration of Pu isotopes with odd A in the core and produces fairly pure Pu in the blanket. H ice the combined Pu product from core and blanket elements has a much higher concentration of fissile Pu isotopes than plutonium from a thermal reactor (the fast breeder not only produces more Pu than it consumes but also improves Pu quality, i.e. increases the conc tration of fissionable isotopes). The LWR and AGR are the poorest plutonium producers. 

As explained in Section II, in a depressurization accident to a gas-cooled reactor (and to some water reactors, e.g., the steam generating heavy water reactor—SGHWR) there is a possibility that can temperatures might rise to about 1000 C at which point some cans could fail through their internal gas pressure. Laboratory experiments in which pre-irradiated fuel elements... 

The French CEA has concentrated on the development of the gas-cooled heavy-water reactor as an advanced converter reactor powerplant 61,62). The design and expected performance characteristics of a 500-MWe plant of this type were reported at the 1964 Geneva Conference (61). The plant would have a gas oulet temperature of 510°C, a steam temperature of 490°C, a steam pressure of 87 atm (1280 psia), and a net plant efficiency of 35 %. Assuming the successful development of a beryllium cladding for the fuel elements, the fuel bumup with natural uranium is expected to be 8700 MW-d/tonne and, with 0.93 % enriched uranium,... 

The product, called uranium ore concentrate (and sometimes yellow cake), contains 65%-85% UjOg, is then shipped to the UCF where the uranium is dissolved and concentrated, and then pnrifled and converted either to the proper form needed for fnel elements (usnally nraninm oxide for graphite type or heavy water reactors) or to the feed material reqnired for isotope enrichment (usually uranium hexafluoride) (Figure 1.10). Following is either fabrication of fuel elements or enrichment to LEU for fneling light water reactors or to HEU for special reactors or nuclear weapons (special nnclear materials (SNM)). The product of the enrichment process, either LEU or HEU, mnst then be converted into the suitable form for the applicatiou— once again nsnally an oxide or metal. 

Heavy nuclides are unstable they can be disintegrated not only by a or P decay or, in some cases, by spontaneous fission, but also by neutron-induced fission. The fission cross sections, however, of the various nuclides show great differences. Among the naturally occurring fissile nuclides is the only one that can be used in thermal reactors in addition, the artificially produced nuclides Pu and Pu show fission cross sections and halflives which make them appropriate for use as nuclear fuels. In the currently operating light water reactors, which are exclusively based on uranium as the starting element, only the fissile nuclides 2 Pu and 2 Pu are of real interest. 

FLORDDO, P C., et al., CARA, new concept of advanced fuel element for HWR, Fuel Cycle Options for Light Water Reactors and Heavy Waters Reactors (Proc. Technical Committee meeting, Victoria, Canada, April 1998) IAEA-TECDOC-1122, Vienna (1999). 

The heavy water reactor was developed in Canada and is known as the CANDU reactor. The D2O is used as both coolant and moderator. The relative moderating efficiency of various materials is given in Table 7.11. Because of the superior moderating property of D2O, it is possible to use natural uranium as the fuel in the form of UO2 pellets in zircaloy tubes. This makes the CANDU one of the best designed reactors in the world. The coolant cycle and the moderator are separate flow circuits shown in Fig. 7.6. The fuel elements in the pressure tubes and the D2O flow is shown in Fig. 7.7 where the coolant is at about 293°C and 100 atm pressure. The moderator is at lower temperature. The efficiency is rated at 29%. ... 

The second class of innovative concepts is liqnid metal-cooled fast-spectrum reactors ( fast-spectrum refers to the energy of the neutrons in the reactor core). In a typical reactor, a moderator (usually water, which pulls double-duty as both neutron moderator and reactor coolant) is nsed to slow down neutrons because slower neutrons are more efficient at causing fission in U-235. In a fast-spectrum reactor, there is no moderator. Instead, it relies on higher energy neutrons, which are less effective at causing uranium to fission but are more effective at causing fission in plutonium and other heavy elements. For this reason, these reactors are not ideal for a uranium-based fuel cycle but they are quite suitable for use with a fuel cycle based on plutonium and the other heavy... 

There were advantages to the new design one was that it used only about one third of the amount of heavy water moderator as the steam-cooled heavy water reactor, and another was that the fuel elements could be clad in zirconium rather than stainless steel. Zirconium absorbs far fewer neutrons than stainless steel, which gave the reactor a much better neutron economy, meaning that the fuel would not need to be enriched as much — the higher the enrichment, the higher the fuel cost. 

The required fabrication capacity for the heavy water fuel element will be in the order of 5-10 x 10 kg/day in the year 2010 for the converter/ breeder cases involving this reactor type. These large plant throughputs will make a reduction of the fabrication costs for these elements very likely 10). The effect of such a reduction was studied by assuming that these costs will reduce from 50/kg to 30/kg. This will have an important effect on system fuel cycle expenditures in the earlier years but a less pronounced effect in the later years, when only a relatively small fraction of the total system capacity will be heavy water reactors. An even further reduction of these fabrication costs to the 20/kg level, that seems possible for very large plant throughputs, would result in savings in the fuel cycle expenditures around 2010 of 0.10 mils/kWh. 

The rapid fission of a mass of or another heavy nucleus is the principle of the atomic bomb, the energy liberated being the destructive power. For useful energy the reaction has to be moderated this is done in a reactor where moderators such as water, heavy water, graphite, beryllium, etc., reduce the number of neutrons and slow those present to the most useful energies. The heat produced in a reactor is removed by normal heat-exchange methods. The neutrons in a reactor may be used for the formation of new isotopes, e.g. the transuranic elements, further fissile materials ( °Pu from or of the... 

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. 

Up to 0.4 g/L of the iodine stays in solution and the rest precipitates as crystallized iodine, which is removed by flotation (qv). This operation does not require a flotation agent, owing to the hydrophobic character of the crystallized element. From the flotation cell a heavy pulp, which is water-washed and submitted to a second flotation step, is obtained. The washed pulp is introduced into a heat exchanger where it is heated under pressure up to 120°C to melt the iodine that flows into a first reactor for decantation. From there the melt flows into a second reactor for sulfuric acid drying. The refined iodine is either flaked or prilled, and packed in 50- and 25-kg plastic-lined fiber dmms. 

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. 

Colorless gas with a strong odor of rotten eggs detectable at 0.005 ppm. However, it can cause olfactory fatigue and the sense of smell is not reliable. Used industrially to produce elemental sulfur, sulfuric acid, and heavy water for nuclear reactors. 

It was detected by Urey, Brickwedde and Murphy in 1932. It occurs in all natural compounds of hydrogen including water, as well as in free hydrogen molecules at the ratio of about one part per 6,000 parts hydrogen. The principal application of deuterium is in tracer studies for measuring rates and kinetics of chemical reactions. It also is used in thermonuclear reactions and as a projectile in cyclotrons for bombardment of atomic nuclei to synthesize isotopes of several transuranium elements. Deuterium oxide, D2O, or heavy water is used as a neutron moderator in nuclear reactors. 

The fuel elements are held in position by grid plates in the reactor core. The fuel burnup to which a reactor may be operated is expressed as megawatt-days per kilogram (MWd/kg), where MWd is the thermal output and kg is the total uranium (sum of U-235 and U-238). In light-water power reactors the core may be operated to about 35 MWd/kg (about 3.5% burnup) before fuel elements have to be replaced. In liquid metal fast breeder reactors (LMFBRs) and high temperature helium gas-cooled reactors (HTGRs), the burnups may exceed 100 MWd/kg ( 10% burnup of the heavy metal atoms). 

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