Uranium once through cycle

Fig. 7.1. Schematic presentations of (a) the once-through cycle (b) the thermal reactor cycle and (c) the fast reactor cycle. UjO, = yellowcake, UF = uranium hexafluoride, MOX = mixed oxide fuel (uranium/...

Fission energy can be obtained from uranium, using the uranium once-through option and the uranium-plutonium fuel cycle, and from thorium, by the thorium-uranium fuel cycle. Each fuel cycle offers a number of alternative routes with respect to reactor type, reprocessing, and waste handling. Although the uranium based cycles are described with special reference to light water reactors, the cycles also apply to the old uranium fueled gas cooled reactors. 

The only major alternative for India is nuclear energy. However, the potential of natural uranium resources, estimated to be around 50,000 tonnes is negligible [about 1 bt of coal equivalent (btce)] if utilised in an once-through cycle and the capacity also will be limited to about 10 GW(e). If the same U along with the Pu generation in PHWR is invested in FBR the... 

In Table IX, the consumption per megawatt(e)-day of energy is indicated for a once-through cycle. The total uranium mined to cover the burnup requirements per megawatt(e)-year, assuming recycle of the bred fuel, is... 

Without any on-site fuel processing, MSRs can run as simple burners with excellent uranium utilization, even on a once-through cycle requiring only a fraction of the input uranium of conventional LWRs. Since even large increases in the price of uranium are acceptable in terms of fuel cycle costs for an MSR burner, the availability of world uranium resources would not become an issue for many centuries at least. 

Thorium-to- U breeders with actinide recycle would produce several orders of magnitude less transuranic waste than a conventional LWR once-through cycle and significantly less than even a U-Pu fast breeder (based on 0.1% losses during fuel processing). This leads to the radiotoxicity of waste being less than the equivalent uranium ore used in LWRs within a few hundred years. 

After launching such factory, the cost of the core will only be determined by the operating costs of spent fuel reprocessing and the costs of fuel assembly fabrication. If the pyro-electrochemical fuel reprocessing methods developed by the State Scientific Centre of the Russian Federation Research Institute of Atomic Reactors (SSC RIAR) are used, the contribution of fuel costs to the cost of SVBR-75/100 will be even less than in the basic variant using a once-through cycle with the uranium dioxide fuel. This will make it possible to improve considerably the NPP competitiveness. The abovementioned approach to the construction of capacities for reprocessing and fuel assembly fabrication presumes that the owner of the NPPs would also be the owner of the fuel cycle factories. 

Meanx hile, success in the development of the natural uranium fuelled CANDU concept had led to very low cost fuelling and effective utilization of uranium even without recovery through reprocessing. AECL therefore decided to set aside work on reprocessing and concentrate instead on the once-through fuel cycle with storage of the irradiated fuel. The evidence indicated that the zirconium clad UO fuel could be stored under water for many decades until a decision was needed regarding recycle or disposal. 

Fuel Recycle. Although the commercial CANDU reactors use the once-through natural uranium fuel cycle, it has been recognized for many years (22) that exceptional uranium utilization could be... 

The heavy arrows in Fig. 21.1 indicate the steps in the nuclear fuel cycle pres dy used on a large commercial scale. The cycle stops at the spent fuel interim storage facility from here two alternative routes are available, one leading to the uranium-plutonium fuel cycle (reprocessing of the spent fuel elements, as described in the next section) and another leading to final storage of the unreprocessed spent fuel elements. The latter is referred to as the once-through fuel cycle (UOT) option. 

The supercritical-water-cooled reactor (SCWR) ( Fig. 58.21) system features two fuel cycle options the first is an open cycle with a thermal neutron spectrum reactor the second is a closed cycle with a fast-neutron spectmm reactor and full actinide recycle. Both options use a high-temperature, high-pressure, water-cooled reactor that operates above the thermodynamic critical point of water (22.1 MPa, 374°C) to achieve a thermal efficiency approaching 44%. The fuel cycle for the thermal option is a once-through uranium cycle. The fast-spectrum option uses central fuel cycle facilities based on advanced aqueous processing for actinide recycle. The fast-spectrum option depends upon the materials R D success to support a fast-spectrum reactor. 

A commercialization option of the GT-MHR started development at GA in 1993 to produce electricity at competitive generation costs and is a promising candidate for near-term commercial deployment in the United States. Two different types of fuel TRISO particles are used for power profiling purposes 19.9% low-enriched (LEU) particles and natural uranium (NU) particles. The design used a once-through fuel cycle, refueling half of the core at every reload interval (Shenoy 1996). 

This fuel cycle is based upon FSV-type fuel, which operated from 1976 through 1989. Fuel composition consists again of two separate TRISO particles, 93% highly enriched uranium (HEU) particles and fertile Th-232 particles to achieve maximum U-233 conversion ratios and therefore limit the amount of plutonium produced. Although HEU-fueled reactors would not be considered for commercial use in the United States, the interest here is historical in nature. This design also uses a once-through fuel cycle, refueling half of the core at every reload interval. 

The fuel cycles used for LWRs utilize uranium enriched to between 3% and 5%. In the United States, there is no fuel reprocessing, so by defaulf this implies a once-through fuel cycle. The used fuel is currently stored either in fuel storage pools or dry cask storage at the reactor sites. The recycle of used fuel has been studied since the early days of... 

---