Thorium-based fuels

A Nonaqueous Reprocessing Method for Thorium-Based Fuels... 

A conceptual pyrometallurgical method for the reprocessing of thorium-based fuels is presented in Fig. 1. It is responsive to the constraints described previously, being operable with either oxide or metal alloy fuel, and producing product streams consisting of enriched uranium/thorium and plutonium/thorium. 

The Idaho Chemical Processing Plant is a versatile, multipurpose facility used for recovering highly enriched uranium from a variety of fuels in naval propulsion, research, and test reactors. Materials processed [Al] include aluminum-alloyed, zirconium-alloyed, stainless steel-based, and graphite-based fuels. The West Valley plant, although designed primarily for low-enriched uranium fuel from power reactors, also processed plutonium-enriched and thorium-based fuels. It is the only U.S. plant to have reprocessed fuel from commercial nuclear power plants. 

The principal types of thorium-based fuel to which the Thorex process has been applied are... 

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. 

Fourth, for comparable reactor systems, the one using a thorium-base fuel will have a larger negative feedback on neutron multiplication with increased fuel temperature (Doppler coefficient) than will a U-fueled reactor. 

Most of the radioactivity in freshly discharged reactor fuel is due to the decays of the fission products (except for thorium-based fuels, where a significant fraction of the external dose is due to the decay of the daughters of During the reactor irradiation, short-lived... 

A Thorium-Uranium Exponential Experltnenti C. If. Skeen and W. W. Broum(AI). Because of uncertainties in the knowledge of t nuclear properties of thorium fuel and lattices containing this fuel, an experimental study was made of a thorium based fuel that is to be loaded into the Sodium Reactor Experiment (8RB) in the near future. An exponential experiment was performed with a square-celled lattice of 7-rod elements (l-in. diameter rods) spaced 9.5 in. apart in praphite. The fuel Is a Th-U-23S alloy containing 7.6% uranium by weight which is 93.13 atomic per cent U-235. The feel elements were 5 ft. long. The subcrltical lattice was placed On thd thermal column of a water boiler reactor which served as the source of neutrons for the assembly. 

One of the major issues of the Thorex process is the creation of a third phase between thorium and TBP if the thorium concentration in the solvent is too high. Furthermore, the partition of uranium and thorium is more difficult than the partition of uranium and plutonium. No change of the thorium oxidation state is required, but the separation of thorium from uranium in the IB contactor must be obtained entirely by a rather delicate adjustment of salting strength inside the contactor. It appears that the Thorex process has been variable in performance. Decontamination from ruthenium has varied and has been particularly poor when short-cooled thorium-based fuel was processed. 

In THORIMS-NES concept, the need of a rapid transfer to thorium-based fuel cycle is justified by the following arguments [XXX-4 to XXX-6, XXX-13, and XXX-15] ... 

XXX-21] INTERNATIONAL ATOMIC ENERGY AGENCY, Thorium Based Fuel Options for the Generation of Electricity Developments in the 1990s, IAEA-TECDOC-1155, Vienna (May 2000). 

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

Periphery (blanket) zone including fuel elements that contain thorium based fuel... 

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

XI-3] ANANTHARAMAN, K., RAMANUJAM, A, KAMATH, H.S., MAJUMDAR, S., VAIDYA, V.N., Thorium based fuel reprocessing refabrication technologies and strategies, INSAC-2000, Annual Conference of the Indian Nuclear Society (Proc. of Annual Conf, Mumbai, 2000). 

Currently, there is an interest in using thorium-based fuels in nuclear reactors. Thorium is widely distributed in nature and is approximately three times as abundant as uranium. However, Th02 does not have any hssile elements to hssion with thermal neutrons. Consequently, Th02 must be used in combination with a driver fuel (eg, UO2, UC, or PUO2), which has as its initial hssile elements. The presence of a driver fuel such as UO2 in a nuclear reactor core results in the production of enough neutrons, which in turn start the thorium cycle. In this cycle, Th is converted into Th, which decays to Pa. Eventually, U, which is a hssile element, is formed by the (3 decay of Pa (Cochran and Tsoulfanidis, 1999). 

The use of thorium-based fuels in nuclear reactors requires information on the thermophysical properties of these fuels. Jain et al. (2006) have conducted experiments on thorium and the solid solutions of Th02 and lanthanum oxide (LaOi 5). As a result of their experiments, Jain et al. (2006) have determined the density, thermal diffusivity, and specihc heat for several compositions of Th02 and LaOi 5 ranging from pure thorium tolO mol% LaOi 5. These properties were measured for temperatures between 100 and 1500°C (Jain et al., 2006). 

Long-term behaviour of a thorium-based fuel.. Nucl. Mater., 282, 180-185. 

---