Heavy-water-moderated

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. 

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... 

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... 

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... 

Plutonium-239 and tritium for use as military explosives are the two major transmutation products. The nuclear process for Pu-239 production is the same as for energy generation, but there are some differences (a) metallic natural uranium clad with aluminum facilitates later dissolution for plutonium recovery, and the reactor operates at a relatively low temperature because of the aluminum clad and better heat transfer (due to the metallic natural uranium) (b) the irradiation cycle is limited to a few months to minimize the Pu-239 conversion to Pu-240 and Pu-241 and (c) a carbon or a heavy water moderator is used to increase the neutron efficiency. 

The Swedish nuelear program was initiated aheady at the end of the 1940 s and had - at that time - both a defenee and a eivilian side. The original Swedish Line for nuclear reactors was to use Swedish natural uranimn, existing in low-grade minerals in the middle of Sweden, in heavy water moderated reactors. 

The first research reactor, located in a rock cavern in Stockholm at the Royal Technical University, was commissioned in 1954. It operated until 1970 and was eventually dismantled in the 1980-s. The site has been decommissioned to green field and the rock cavern is now used for other activities without any radiological restrictions. Several research reactors were also operated in the nuclear national research laboratories in Studsvik. From 1964 to 1974 a heavy water moderated PWR reactor was operated for district heating purposes in a suburb to Stockholm but also generating electricity. It was intended as a demonstration facility. It is now waiting dismantling. 

AECL is developing a supercritical heavy water moderated nuclear reactor (SCWR) [2] based on its successful CANDU reactor system currently deployed around the world. Since the Mark 2 [2] version of the heavy water moderated SCWR can satisfy the temperature requirements of the hybrid Cu-Cl cycle, AECL is collaborating with ANL in the development of this cycle. Also, AECL is particularly interested in this process since some of its hydrogen-economy related technologies are a good match for the developmental needs of this process, in particular for the development of the electrochemical step involved. 

An Evaluation of Heavy-Water-Moderated Organic-Cooled Reactors, Report WASH-1083, Mar. 1968. 

In the CANDU heavy-water reactor the dominant source of tritium is the deuterium activation reaction of Eq. (8.53). The data given in Prob. 3.3 for the Douglas Point Nuclear Power Station provide a basis for estimating the rate of production of tritium in the heavy-water moderator and coolant ... 

The organic-cooled CANDU concept was proposed by McNelly of CGE in 1958 (71), This began an extensive investigation of coolant properties, decomposition, control of deposition, and many other aspects of coolant chemistry. An organic-cooled, heavy-water-moderated research reactor, WR-1, began operation at WNRE in 1965. It has demonstrated reliable operation with coolant outlet temperatures of up to 675 K. Low corrosion and a low potential for activity transport result in very low radiation fields around the piping. 

Power Heavy-Water-Moderated Nuclear Reactors, Atomic Energy of Canada Limited Report, AECL-797, 1959. 

The pile at Haigerloch had served for the KWI s final round of neutron-multiplication studies. One and a half tons of carefully husbanded Norsk-Hydro heavy water moderated it its fuel consisted of 664 cubes of metallic uranium attached to 78 chains that hung down into the water from the metal shield Pash describes. With this elegant arrangement and a central neutron source the KWI team in March had achieved nearly sevenfold neutron multiplicatioi Heisenberg had calculated at the time that a 50 percent increase in the size of the reactor would produce a sustained chain reaction. 

One of the most important reasons for using a small-volume light water— moderated core instead of the large-volume heavy water—moderated core described in MonP-108 and in pendix 1 is that the virgin neutron flux (fission neutrons which have suffered no collisions) and the y-ray flux are much higher. The virgin flux, is related to the number of fission neutrons... 

The old proposed heavy water—moderated reactor had a core volume almost ten times greater than the present one, while the total power output, 3 10 kw, and virgin—neutron mean free path was the same. Its average virgin flux was thus smaller by a factor of 10. A comparison of the slow, resonance, and fast flux in these light water and heavy water reactors is given in Table 4. 2.A. 

Reactor. Heavy water moderated research reactor. 

Reactor. Experimental heavy water moderated, carbon dioxide cooled pressure tube reactor. 

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