Fuel Cycle Options Research Articles

Non-proliferation criteria for nuclear fuel cycle options

We compared the implied meaning of proliferation resistance in proposals regarding the nuclear fuel cycle. We find discrepancies amongst the proposals regarding the technical definition of proliferation resistance, however there is a consistent focus on the importance of “physical form” as a key in determining a proliferation resistant fuel cycle. The reviewed proposals make little explicit mention the importance of the time to process the material to construct a nuclear weapon. While certain proposals discuss the importance of non-separation of plutonium from actinides, there are other proposals, which clearly do not view this aspect as vital in defining proliferation resistance. Recognizing that there are numerous political and infrastructure measures that may also be taken to guard against proliferation risks, we have focused here on the definition of proliferation resistance in terms of technical characteristics.

Desirability of small reactors, HTGR in particular

Small reactors of about 100–300 MWe, High Temperature Gas Cooled Reactors (HTGRs) in particular, are considered desirable in future, based on the following ways of thinking; Global scale enhancement of nuclear energy is considered necessary from reduction of environment impact point of view. Small reactors are desirable, due to (a) enhanced safety in terms of fuel inventory and inherent safety, then (b) easier plant siting, near populated or industrial area, (c) more flexible development, planning and construction than larger reactors by finer adjustment with demand, and (d) economic competitiveness attainable by means of adoption of more rationalized systems categorization, simpler and modularized design, mass production in factory, less work at construction site, and marketability including that of developing countries. In such ways, small reactors can be economically designed, constructed and operated, by conquering “scale de-merit”, in contrast with scale merit of larger reactors as seen in current LWRs. Small HTGRs, in particular, are mostly desirable and promising, from view points of wider applications, such as electricity use, wide range of heat uses and/or cogenaration, Pu burning with high efficiency, wider fuel cycle options, using U, Pu and/or Th, with or without reprocessing, and development stages, where not only test reactor programs for development & demonstration but also realization programs are already going on towards commercial operation start in 2005–2010. Development programs on small HTGR, related global activities and cost evaluations by developers and JAPC are shown, and steps towards their global scale commercializations are proposed.

Non-proliferating reprocessed nuclear fuels in pressurised water reactors: Fuel cycle options

Many alternatives have been studied in the attempt to burn Plutonium produced in the last decades. Among these, there are the reprocessing of the Plutonium and the insertion of Thorium in thermal reactors. Nevertheless, the proliferation risk is always associated with conventional reprocessing techniques, such as PUREX. Hence, alternative reprocessing methods with low-grade decontamination and uranium-plutonium co-extraction characteristics have been proposed. Besides that, the insertion of Thorium in fuels coming from PUREX has shown good results. Therefore, based in these data, fuels coming from alternative techniques of reprocessing such as Coprocessing and AIROX, have been analysed, with and without the insertion of Thorium. The goal is study fuel options with good neutronic and environmental performance.

Nuclear fuel cycle cost analysis using a probabilistic simulation technique

A simple approach was described to incorporate the Monte Carlo simulation technique into a fuel cycle cost estimate. As a case study, the once-through and recycle fuel cycle options were tested with some alternatives (ie. the change of distribution type for input parameters), and the simulation results were compared with the values calculated by a deterministic method. A three-estimate approach was used for converting cost inputs into the statistical parameters of assumed probabilistic distributions. It was indicated that the Monte Carlo simulation by a Latin Hypercube Sampling technique and subsequent sensitivity analyses were useful for examining uncertainty propagation of fuel cycle costs, and could more efficiently provide information to decisions makers than a deterministic method. It was shown from the change of distribution types of input parameters that the values calculated by the deterministic method were set around a 40 th∼50 th percentile of the output distribution function calculated by probabilistic simulation. Assuming lognormal distribution of inputs, however, the values calculated by the deterministic method were set around an 85 th percentile of the output distribution function calculated by probabilistic simulation. It was also indicated from the results of the sensitivity analysis that the front-end components were generally more sensitive than the back-end components, of which the uranium purchase cost was the most important factor of all. It showed, also, that the discount rate made many contributions to the fuel cycle cost, showing the rank of third or fifth of all components. The results of this study could be useful in applications to another options, such as the DUPIC (Direct Use of PWR spent fuel In CANDU reactors) cycle with high cost uncertainty.

Value of nuclear power in the global energy system

With a global energy model which finds the minimum cost energy system over the time range of 1995–2055, the value of nuclear power is analysed. The model incorporates detailed descriptions of energy conversion technologies. For nuclear technologies, light water reactors and fast breeder reactors are taken into account with fuel cycle options. Major findings are: 1) the maximum introduction of LWRs would have only a small effect in reducing the global CO2 emissions; 2) FBRs would be introduced at the almost maximum scale when the stabilisation of global CO2 emission is required; 3) the role of FBRs in reducing the global CO2 emission is very robust against the deterioration of their economics; and 4) integrated coal gasification combined cycle power generation (IGCC) with CO2 recovery would replace the role when FBRs are not introduced.

Nuclear power in the global energy-environmental system

Reducing the CO2 emission to cope with the global warming is one of the most challenging issues for the global energy system. Among various technological options for reducing the CO2 emissions from energy production, nuclear power is expected to play a key role if accepted by the society. However, there have been fewer model analyses reported recently on the role of nuclear power in the global energy system when compared with the analyses of the other options such as energy efficiency improvements, renewable energies, and CO2 recovery and disposal. This paper presents, with a newly developed global energy model, a numerical analysis on the value of nuclear option in the global energy system, particularly in terms of CO2 mitigation. With the global energy model, which finds the cost minimum energy system over the time range of 1995–2055, the value of nuclear power is analyzed. The model incorporates detailed descriptions of energy conversion technologies which include, besides electricity generation, various liquefaction and gasification processes of hydrocarbon fuels with the options of CO2 recovery and disposal. For nuclear technologies, LWRs (light water reactors) and FBRs (fast breeder reactors) are taken into account with fuel cycle options. Major findings are: 1) LWRs would be introduced at the maximum level into the cost minimum energy system if their economics is slightly improved from the standard assumption; however, 2) the maximum introduction of LWRs would make only a small effect in reducing the global CO2 emissions; 3) FBRs would be introduced at an almost maximum scale when the stabilization of global CO2 emission is required; 4) the role of FBRs in reducing the global CO2 emission is very robust against the deterioration of their economics; and 5) IGCC (integrated coal gasification combined cycle power generation) with CO2 recovery would replace the role when FBRs are not introduced.

A Pressurized Water Reactor Design for Plutonium Incineration: Fuel Cycle Options

The possibility exists of utilizing pressurized water reactor (PWR) power plants of current technology for efficient and cost-competitive incineration of excess plutonium. Several plutonium-based fuel cycle options were considered, i.e., pure 239Pu or reactor-grade plutonium as a fissile component and natural uranium or thorium as a fertile component of the fuel.A typical PWR was chosen as the base for detailed analysis and comparison of all investigated fuel cycle options. A series of calculations was carried out for each of the fuel cycle options generating “equilibrium” cycles of equal length.Results of the design analysis and comparison of main performance parameters were used to compare different fuel options. Material mass balances were calculated to evaluate the plutonium incineration potential of the considered options. A potential of efficient reduction of excess plutonium was demonstrated for all considered fuel options. The thorium-based fuel cycles were found especially effective for destruction of fissile isotopes of plutonium (>1000 kg/yr). This was partially compensated by the buildup of 233U isotope. One of the important conclusions of this work is that significant amounts of fissile plutonium may be incinerated in thorium-based cycles and that 233U may be denatured by addition of modest amounts of natural uranium. Preliminary economic evaluations indicate that plutonium incineration may be carried out in existing PWRs without economic penalty and may, therefore, present a viable alternative to other plutonium disposition methods.

Some Computations in Planning Reconstitution of a 500-MW(electric) Fast Breeder Reactor (Metallic) Fuel by Electrorefining

To compare and evaluate various fuel cycle options for a 500-MW(electric) fast breeder reactor, the electrorefining process has been examined for reprocessing spent fuel. Making use of an improved thermochemical model, optimum process conditions for electrorefining have been worked out. These conditions are the following: capacity of the electrorefining cell, number of cells, batch size, feed adjustments, sequential operations for recovery of uranium and co-recovery of uranium and plutonium, number of cycles, and timeframe to meet the refueling schedule. The spent fuel is envisaged to undergo reprocessing in three campaigns: (a) the inner core campaign, (b) the outer core campaign, and (c) the blanket and the leftover campaign. Feed adjustments are done by mixing either the spent inner core or the outer core fuels with the blankets. Three product streams with required fuel composition for direct refabrication of the inner core, the outer core, and the blanket fuel subassemblies, respectively, are obtained by certain sequential electrorefining operations. These calculations made for a mixed-oxide fuel core can be easily extended to the metallic core.

A new hazard index for the determination of risk potentials of disposed radioactive wastes

On the basis of a discussion of advantages and limitations of hazard calculations of nuclear waste, a new hazard index is presented. The model deals with environmental processes that determine radiation exposure to man after failure of a geologic repository and release of radionuclides into the biosphere. Included in the model are isotopic composition of the waste, probability for transport of nuclides to man, cycling in the biosphere, radiotoxicity to man and changes of the risk potential which are due to radioactive build-up and decay processes after the waste nuclides enter the biosphere. Nuclide-specific data necessary for the use of the new index are compiled. Calculations for wastes from different nuclear power reactor types and fuel cycle options indicate that 237Np and 241Am are the waste constituents with the most demanding requirements in regard to the long-term isolation potential of a repository. Isolation times required for the wastes analyzed are of the order of 10 7 years. Hazard analyses of nuclear wastes with negligible heat generation from various sources show that secondary wastes from nuclear fuel reprocessing and mixed-oxide fuel fabrication have long-term risk potentials which are about two orders of magnitude higher than those from other wastes. They should be disposed of together with high-level wastes.