Once-through cycle

The diagram in Figure 16.1 shows two possible paths for this cycle, that is, with and without fuel reprocessing. The majority of reactors in the world and all U.S. reactors operate with a once-through cycle without reprocessing. Some countries, particularly France, do fuel reprocessing with reuse of the plutonium from spent fuel. The portions of the cycle, that precede the introduction of the fissile material into the reactor are referred to as the front end of the cycle, while the back end includes those steps that occur after the removal of the fuel from the reactor. The details of this cycle and the chemistry involved are discussed below. 

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/...

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... 

Reactor U 5 feed fuel Recycle with makeup Once-through cycle (throwaway)... 

Once through cycle with direct disposal of spent fuel as HLW. 

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. 

The major resource advantage over other burner designs may seem surprising given that a conversion ratio of 0.8 does not appear that much superior to LWR and PBMR (both 0.5-0.6) or CANDUs (0.7). However, conversion ratios do not take into account the limited residency time of fuel in solid-fueled reactors. Perhaps, a new term of effective conversion ratio would be to compare fissile consumption versus needed annual fissile additions. By this metric, most other reactors on a once-through cycle have effective conversion ratio of near zero since they consume about 1000 kg/GWe-year but need to add 1000 kg of fissile 235 U per year. Even with Pu recycle, they do not improve significantly. Thus, the great... 

The 4S Toshiba Design (14) uses U-Zr alloy fuel in a once-through cycle to achieve early deployment the 4S-LMR CRIEPI Design (15) uses U/TRU/Zr alloy fuel based on reprocessed LWR spent fuel as a source. 

Waste management benefits accrue to the multiple transuranic recycle of a feedstock symbiotically recovered from once-through cycle concepts, facilitating that only fission products are consigned to the waste destined for geologic disposal ... 

Fuel cycle type Once-through cycle at the initial stage... 

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. 

The MARS fuel cycle is a standard, once-through cycle, typical of PWRs. Innovative fuels are compatible for use in the MARS NPP. 

The alternative fuel cycle option is a once-through cycle with cermet fuel (micro-particles of fuel in a metallic matrix). 

In the reference once-through cycle, the fuel would be supplied by fuel manufacturing organizations, likely to be organizations currently supplying water reactor fuel. Each fuel supplier would be required to qualify its product by irradiation and post irradiation testing of sufficient quantities of fuel representative of the production fuel, and by certification of compliance with fuel fabrication process and product specifications. 

To satisfy this demand in the medium and long term, is impossible if the world remains restricted to the once-through cycle. 

The plutonium cannot be completely burned in a once-through cycle because of fuel burnup limits and the statistical improbability of all plutonium being struck by a neutron. However, with the right fuel choice perhaps 70-95% can be burned. The remaining 5-30% could then be extracted via reprocessing and returned to a reactor. Thus, a fraction of the entire plutonium stockpile could be burned in one concept in a couple of... 

Stability is maintained by increasing orifice pressure drop in the design. The pumping power increases with the total pressure drop, but it is not a problem in the once-through cycle reactor. The pump is powerful and pumping power is not excessive because of the small reactor coolant flow rate. 

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