Thorium fuel cycle

FIPS [Fission Product Solidification] A process for immobilizing the radioactive waste products from the thorium fuel cycle in a borosilicate glass for long-term storage. Developed at Kemforschungsanlage Jiilich, Germany, from 1968, until abandoned in favor of PAMELA in 1977. 

Research and development activities for thorium fuel cycles have been conducted in Germany, the USA, India, Japan, Russia and the UK during the last 30 years at a much smaller scale than uranium and uranium-plutonium cycles. Nowadays, India, in particular, has made the utilisation of thorium a major goal in its nuclear power programme, as it has ambitious nuclear expansion plans and significant indigenous thorium resources. 

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... 

Stover BJ. 1981. Toxicology of thorium-228 in young adult beagles Potential relationship to the thorium fuel cycle. In Wrenn ME, ed. Actinides in Man and Animals Proc Snowbird Actinide Workshop. R D Press, University of Utah, Salt Lake City, UT, 483-500. 

Levine, H.S., "Conversion of Fuel Hulls to Zirconate Ion Exchanger for Stabilization of Wastes from the Thorium Fuel Cycle," Symposium on Waste Management and Fuel Cycles "78," Edited by R.G. Post and M.E. Wacks, Tucson, AZ, March (I978). 

Akiba, K. and Nakamura, S., Transport of metal species through supported Uquid membrane containing dihexyl-A,A-diethylcarbamoyl methylenephosphonate. in Chemical Aspects of Down Stream for Thorium Fuel Cycle, Suzuki, S., Mitsugashira, T., Hara, M., Satoh, I., and Shiokawa, Y., Eds., Atomic Energy Society of Japan. Tokyo (Japan), 1987, pp. 85-90. 

Another feature of the thorium fuel cycle which affects reprocessing is the buildup of 232U in the irradiated fuel. 

The Acid-Thorex process has been used in recent years to recover 233U from neutron irradiated thoria targets. (] M This process uses n-tributyl-phosphate (TBP) in normal paraffin hydrocarbon (NPH) as the extractant and the relative uranium and thorium solubilities in each phase are adjusted by control of the nitric acid concentration. The Acid-Thorex process is the primary candidate for use in proposed aqueous thorium fuel cycles. In this process, uranium is separated from thorium through exploitation of the difference in equilibrium distributions since no usable valence change is available to aid in this separation. 

Jr. Wible, A. E., Recovery of 33U from Irradiated Thoria in MThorium Fuel Cycle-Proceedings of Second International Thorium Fuel Cycle Symposium, Gatlinburg, Tennessee, May 3 6,... 

Another problem of the thorium fuel cycle results from the radioactivity of 72-year and its dau ters. is formed by (n, 2n) reaction with Th according to... 

Relatively little Pu, Pu, Pu, americium and curium are formed in the irradiation of thorium-uranium fuel with fissUe makeup. However, when plutonium is used as fissile makeup for a thorium fuel cycle, considerable quantities of americium and curium are formed. As discussed in Sec. 2.4, these are the radionuclides that are the greatest contributors to radioactivity and ingestion toxicity after about 600 years of waste isolation, when the fission products have decayed. 

The toxicity of the high-level wastes from a uranium-thorium HTGR fuel cycle is initially smaller, after the fission-product decay period of 600 years, because of the relatively small quantities of americium, curium, Pu, and Pu formed in this thorium fuel cycle. However, after about 100,000 years of isolation the theoretical ingestion toxicity of the wastes is governed by Ra, formed by... 

P3. Pigford, T. H., and C. S. Yang Thorium Fuel-Cycle Alternatives, Report EPA 68-01-1962, UCB-NE3227, 1978. 

R5. Rathvon, H. C., et al. Recovery of with Low Content, Proceedings of the 2nd International Thorium Fuel Cycle Symposium, Gatlinburg, Tenn., May 1966, USAEC CONF-660524, 1966, pp. 765-824. 

Interest now is centered on the thorium cycle (23) and laboratory studies have continued to investigate both an adaptation of the Thorex process to CANDU fuel and the application of the amine process to recovering uranium-233 from irradiated thorium. The program to develop and fully demonstrate the thorium fuel cycle has been outlined, and would require about 25 years to complete. However, the current research level will not be expanded until a decision can be taken by the Canadian Government when the information from the current International Nuclear Fuel Cycle Evaluation has been assessed. 

In the thorium fuel cycle the recycled uranium-233 inevitably is contaminated with uranium-232 and its decay products. The first of these, thorium-228, will be contained in any recycled thorium. Thallium-208 in this decay chain emits a very-high-energy gamma ray and for this reason fabrication of recycle fuels in the thorium fuel cycle will have to be done remotely in heavily shielded cells. Conventional fuel febri-cation processes may not be the most economical under these conditions. 

The sole reason for using thorium in nuclear reactors is the fact that thorium ( Th) is not fissile, but can be converted to uranium-233 (fissile) via neutron capture. Uranium-233 is an isotope of uranium that does not occur in nature. When a thermal neutron is absorbed by this isotope, the number of neutrons produced is sufficiently larger than two, which permits breeding in a thermal nuclear reactor. No other fuel can be used for thermal breeding applications. It has the superior nuclear properties of the thorium fuel cycle when applied in thermal reactors that motivated the development of thorium-based fuels. The development of the uranium fuel cycle preceded that of thorium because of the natural occurrence of a fissile isotope in natural uranium, uranium-235, which was capable of sustaining a nuclear chain reaction. Once the utilization of uranium dioxide nuclear fuels had been established, development of the compound thorium dioxide logically followed. 

A thorium fuel cycle is also possible for use in nuclear power reactors. This involves using thorium-232 to generate uranium-233, which is capable of undergoing fission processes to generate energy in the form of heat. 

In 1996, all scheduled studies on the uranium-thorium fuel cycle were completed on the CBR-22 critical assembly with the core containing metal enriched uranium and metallic thorium. The high enrichment of the core fuel ( 20%) caused quite rigid neutron spectrum (neutron fraction having energy lower than 10 KeV did not exceed 1%). 

Ottewitte, E.H., 1982. Gonfigurations of a Molten Chloride Fast Reactor on a Thorium Fuel Cycle. PhD Thesis, UCLA, Los Angeles, CA. 

The abimdance of thorium in the earth s crust is about three times that of uranium. Hence, the thoriiun fuel cycle ensures a long-term nuclear fuel supply. For countries with abundant thorium reserves, the thorium fuel cycle in HWRs would enhance the sustainability of nuclear power and the degree of energy independence using a single reactor type. 

Because thorium itself does not contain a fissile isotope, neutrons must be initially provided by adding a fissile material, either within or outside the Th02 itself. How the neutrons are initially provided defines a variety of thorium fuel-cycle options in HWRs that will be examined in this section. These include the following ... 

One of the advantages often cited for the thorium fuel cycle is a significant reduction in the production of long-lived transuranic actinides. It has lower "radiotoxicity" than uranium-based fuels, and so fhe source term in the waste management vault will be lower. 

Boczar, P.G., P.S.W. Ghan, G.R. Dyck, and D.B. Buss. 1999. Recent Advances in Thorium Fuel Cycles for CANDU Reactors, Proceedings of the IAEA Technical Committee Meeting on Utilization of Thorium Fuel, November 17-19, Vienna, Austria. 

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