Uses of Thorium

Thorium is important in nuclear technology as the naturally occurring fertile nuclide from which neutron capture produces fissile by the succession of reactions 

In thermal-neutron reactors has an important advantage over or Pu in that the number of neutrons produced per thermal neutron absorbed, tj, is higher for than for the other fissile nuclides. Table 6.1 compares the 2200 m/s cross sections and neutron yields in fission of these three nuclides. Thorium has not heretofore been extensively used in nuclear reactors because of the ready avaUabihty of the U in natural or slightly enriched uranium. As natural uranium becomes scarcer and the conservation of neutrons and fissile material becomes more important, it is anticipated that production of U from thorium will become of greater significance. 

Compared with Pu, the other synthetic fissile nuclide, has the advantage that it can be denatured, made less available for use as a nuclear explosive, by isotopic dilution with in a mixture containing less than 12 percent Production of a nuclear explosive from such a mixture would require costly and difficult isotope separation (Chap. 14). No similar means exists for denaturing Pu, which can be more readily separated from by chemical reprocessing (Chap. 10). 

In addition to its potential use in nuclear power systems, thorium has had minor industrial use in Welsbach mantles for incandescent gas lamps, in magnesium alloys to increase strength and creep resistance at high temperatures, and in refractories. 

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Thorium is used to make ceramics, lantern mantles, and metals used in the aerospace industry and in nuclear reactions. Thorium can also be used as a fuel for generating nuclear energy. More than 30 years ago thorium oxides were used in hospitals to make certain kinds of diagnostic x-ray photographs. Further information on the properties and uses of thorium can be found in Chapters 3 and 4 of this profile. 

In order to make use of thorium as a nuclear resource for power generation, development of efficient separation processes are necessary to recover 233U from irradiated thorium and fission products. The THORium uranium Extraction (THOREX) process has not been commercially used as much as the PUREX process due to lack of exploitation of thorium as an energy resource (157,180). Extensive work carried out at ORNL during the fifties and sixties led to the development of various versions of the THOREX process given in Table 2.6. The stable nature of thorium dioxide poses difficulties in its dissolution in nitric acid. A small amount of fluoride addition to nitric acid is required for the dissolution of more inert thorium (181). 

Recently much attention has been given to the accelerator driven systems, burning in inert matrices, and the use of thorium to burn plutonium. The concept of a closed nuclear fuel cycle was traditionally considered as transmutation (burning) of only plutonium and recycled uranium, with minor actinides (neptunium, americium, curium) destined for final geological disposal. But as time goes on, a new understanding is emerging reduction of the quantity of actinides would ease requirements for final repositories and make them relatively less expensive. 

Use of thorium has decreased substantially in recent years. This is due to its radioactivity and the costs associated with monitoring its use and disposing of it safely. 

Beeause of the radiation effects of thorium, the use of thorium dioxide is limited only to the procedures approved by the U.S. Food and Drug Administration, such as hepatolienogra-phy in patients with metastatie eaneer (39). 

Numerous patents6 have been issued for the use of thorium chromate, thorium tungstate, and other salts in the preparation of magnesium flashlight powders. It is claimed that such powders evolve les,s smoke than those which consist of magnesium alone. 

The only important commercial use of thorium, however, is in the manufacture of incandescent gas mantles. This industry had a very modest beginning in 1884 when Welsbach patented the use of a fibrous network of rare earth oxides which were to be heated by an ordinary gas flame of the Bunsen type. The first mantles were composed of a mixture of zirconia, lanthana,... 

In 1996, static and dynamic calculations are being performed on the 20MWth PAP-GT of KFA Julich and compared to their calculations with different codes. For this reactor type, fuel temperatures are maximal in the scenario of depressurization with recriticality. Even for this scenario, fuel temperatures do not exceed 1300 C, so there should be room for upscaling for economic reasons. On the other hand, it would be convenient to fuel the reactor batchwise instead of continuously, and the use of thorium could be required. These two features may lead to a larger temperature margin. The optimal design must unite these features in the best acceptable way. 

M. Ishltoashl, T. PuJ lnaga and Y. Kusaka, "Chemical Studies on Radioactive Indicators XVIII. Controlled Potential Electroseparation of Copper, Bismuth and Lead and Its Radioactive Indication toy Use of Thorium B and Thorium C Tracers", J. Chem. Soc. Japan 75, 13 (1954). 

The nuclear fuel cycle starts with the ore being extracted from the earth and follows it through processing and use until a final waste form is placed back for permanent disposal. Both uranium and thorium exist in nature as minerals that can be mined however, uranium will be used in this discussion because the use of thorium has not been extensively... 

OTT cycles, where the rationale for the use of thorium does not rely on recycling the (but where recycling remains a future option)... 

Thorium was first discovered by Berzelius in 1828. Thorium, like uranium, is a nuclear fuel, but the use of thorium fuel, unlike the use of uranium, has been nearly forgotten. While uranium technology in pressurized water reactors (PWRs) has been shown to be dependable... 

Table 4.121. Industrial applications and uses of thorium Applications Description...

Thorium is found in nature as the mineral thorite, Th02, and in mona-zite sand, which consists of thorium phosphate mixed with the phosphates of the lanthanons (Section 18-7). The principal use of thorium is in the manufacture of gas mantles, which are made by saturating cloth fabric with thorium nitrate, Th(NOa)4, and cerium nitrate, Ce(N03)4. When the treated cloth is burned, there remains a residue of thorium dioxide and cerium dioxide, Th02 and Ce02, which has the property of exhibiting a brilliant white luminescence when it is heated to a high temperature. Thorium dioxide is also used in the manufacture of laboratory crucibles, for use at temperatures as high as 2300°C. 

Enhanced proliferation resistance Use of thorium based TRISO type fuel. 

The use of thorium fuel leads to suppression of the generation of minor actinides in the nonplutonium bearing CHTR. Graphite based fuel tubes with low activation and ease in compacting the waste further reduce the amount of wastes generated. An isotope of a certain concern in the thorium cycle is It is formed via (n, 2n) reactions, from Th, Pa and and has a half-life of about 69 years. The daughter products of are hard gamma emitters like T1 (2.6 MeV) with very short half-lives. As a result, the radioactivity increases... 

Use of thorium-based fuels with low fissile inventory and maintaining the negative fuel temperature coefficient of reactivity throughout the reactor operation ... 

Mining, milling and processing of thorium ores, and the use of thorium and its compounds (which can lead to internal exposure due both to radioactive dusts and to thoron ( Rn) and its progery) ... 

The use of thorium fuel based on the RTR concept can ensure that neither fuel loaded in the reactor nor fuel discharged from the reactor could be used for nuclear weapons production the plutonium recovery could be decreased by 4 to 5 times. 

The use of thorium as fuel practically leads to elimination of the generation of minor actinides from a non-plutonium bearing fuel of AHWR. The major design provisions of AHWR that have a potential to reduce dose levels in the reactor are on-line refuelling, the use of light water instead of heavy water and hence the reduction in tritium activity, easily replaceable coolant channels, and the accessible design of layout and equipment to simplify in-service inspections. 

Use of thorium based fuel Nuclear data for nuclides important for the thorium cycle A critical facility is under constmction... 

The flexibility of possible fuel cycles for the GT-MHR supports future options with increased fuel utilization, including efficient use of thorium, if enabled by an infrastmcture supporting fuel reprocessing [XV-5]. 

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