Natural uranium equivalent fuel cycle

The quantity of natural uranium to be mined for the production of the heavy metal reprocessed. This type of reference has already been used in Chap. 8 because it is the most general one with no special assumption about the form of the natural uranium involved. Its disadvantage is the strong dependence on fuel-cycle type. With an equilibrium LMFBR fuel cycle, for instance, the quantity of uranium to be mined becomes close to zero and, consequently, the period of significance of the waste hazard becomes extremely long. To maintain its applicability, the uranium equivalent must always be calculated on the virtual basis that all power has been generated from freshly mined uranium. 

Transmutation of long-lived nuclides (actinides and fission products) in the fuel cycle of fast reactors should proceed, at least, until the biologically equivalent activity of the waste to be buried declines to that of the natural uranium consumed (this condition is referred to as equivalence in terms of radiation and biological hazards). Notably, such equivalence may be attained both by the time of burial and within a historically short and reliably predicted period of, e.g., 200-1,000 years. This approach allows reasonably minimizing the mass and hazard of long-lived waste, while the specific conditions of waste disposal should meet the national regulatory requirements. 

Fuel-Cycle Option Natural U Consumption MgU/GW(e)a Uranium Utilization MW(e)d/Mg UasU,0, Equivalent Natural U Bumup MW(th)-d/kg NU Spent Fuel Arisings MgHE/GW(e)a... 

The fuel cycle feedstock is natural or depleted uranium, and multi recycle through sequential cassette reload cycles achieves total fission consumption of the feedstock only fission product waste forms (and trace losses of transuranium nuclides) go to a geologic repository operated by the regional centre. These waste forms - lacking any transuranic component -decay to the equivalent radio toxicity levels of the original ore within 200-300 years... 

Before discussing the sustainability of Gen-IV systems, a reminder about natural uranium and the composition of spent nuclear fuel (SNF) is necessaryNatural uranium is composed of 0.005% U, 0.720% U%, and 99.275% U. The fuel used in a standard LWR relies on the fissile isotope U, which is typically enriched to U concentrations in the range of 4%. However, it should be noted that some 40% of the energy produced in the course of a nuclear fuel cycle in an LWR comes from Pu, which is thus an excellent fissile fuel material. Moreover, ceramic-mixed oxide fuel (MOX, which is UO2 + PUO2), consisting of about 7—10% Pu mixed with depleted uranium ( U), is equivalent to UO2 fuel enriched to approximately 4.5% U, assuming that the Pu contains approximately two-thirds fissile isotopes. 

The power density of the reactor core is typically lower in a natural circulation reactor than in a forced circulation reactor, but the lower power density allows a longer continuous operation. The short heated length of the fuel and the low power density provide good thermal-hydraulic characteristics. With the 8 x g type fuel assembly selected, the power density is 34.2 kW/L the number of fuel assemblies is 708, and the equivalent core diameter is 4.65 m. The uranium enrichment of the refuelling batch, at equilibrium, is 3.6%, and the average fuel burn-up is 39 GWd/t for operation cycles of 23 months. 

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