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The Nuclear fuel cycle: analysis and management by Robert G Cochran · The Nuclear fuel cycle: analysis and management. by Robert G Cochran; Nicholas. Issuu is a digital publishing platform that makes it simple to publish magazines, catalogs, newspapers, books, and more online. Easily share. PDF | Nuclear power has unresolved challenges in long-term management of radioactive wastes. A critical factor for the future of an expanded nuclear power industry is the choice of the fuel cycle—what type of fuel is used, what types of Design, analysis and development of the modular PB-AHTR.
This aspect makes it possible to transmute the TRUs and extract energy at the same time. In this cycle, a sodium-cooled fast reactor SFR with a conversion ratio of 0. The metal fueled SFR using alloys of actinides zirconium AcZr has a high potential for recycling actinides by being integrated with the pyroprocessing. The material flow values in Figure 1 were calculated using the equilibrium model based on an output of 1 TWh of electricity, a detailed description of which refers to the previous material flow study [ 9 ].
It is difficult to estimate the absolute value of each of the components specified in Figure 1 because many uncertainties exist. Therefore, a range of unit cost i. The nominal value refers to the best estimated unit cost. The lower bound means the low cost case, and the upper bound means the high cost case [ 5 , 11 ]. Taking no account of the reactor capital cost, therefore, largely reduces the uncertainty of the SFR, and therefore enhances and emphasizes the contribution of the fuel cycle to the total electricity cost.
The summarized data before converting to the values are listed in Table 1. Some specifications of the key components are described as follows. The difference mainly lies in the technical readiness and the considerations on proliferation resistance PR as stated in the AFCCB reports. In our study, we admit the big gaps among different countries concerning the status of MOX fuel fabrication technique.
In addition, the PR is definitely important for the future deployment of the fuel cycle, and therefore, the bigger unit cost from the US study was adopted. Table 1: Unit costs for nuclear fuel cycle steps. It is challenging to project the future uranium price due to the complexity of the price determinants, such as supply and demand.
It seems to be obvious that the newer reports suggest a wider range of uranium price. Figure 2: Uranium spot prices. It is reasonable to doubt the relatively lower prediction of the uranium price. However, the reason for the adoption of the peak value in this study is to enlarge the possible range of the uranium price to better reflect the high uncertainty of the future uranium price.
Conversion and Enrichment The nominal price of conversion and the enrichment processes are from the monthly price of December of Pyrotechnique Cost As no commercial experience exists, the unit costs concerning the pyrotechnique for fuel reprocessing are theoretical and estimated using engineering judgments with high uncertainty.
Because of the difference of the fuels treated and a big gap between the material flows evolved, there are two pyrotechnique-related components in the Pyro-SFR recycling scenario.
Storage Cost It is assumed that the interim storage cost consists of two parts: a fixed cost and a variable cost depending on the storage time, which was set for 5 years in this paper [ 1 , 5 ]. The decay storage of Cs and Sr which are main heat emitters separated by pyroprocessing, employs a shallow disposal as a low-interim level waste for around — years [ 18 ].
Fuel Cycle Cost Calculation 4.
Lead and Lag Time The costs depend on the amount of material or service consumed and the unit price of each component. The payments for the various components of the nuclear fuel cycle are usually made at different moments in time. Each step-cost should be calculated with consideration of its implementation time, starting from the fuel download costs and ending to the final disposal costs.
It is therefore reasonable to consider the discount rate to compare all the payments at the same time according to the refueling interval plus or minus a lead or lag time as listed in Table 3. Fuel Cycle Cost The amount of fuel passing through a certain step multiplied with the unit cost of the specific material offers the fuel cost of a single step and combined with the additional cost associated with the operation, the overall cost of an operation, namely, the component cost, can be obtained.
The method employed for the calculation of FCC is the constant money levelized life-time cost method. The levelized unit cost is based on the cash flow of all component costs discounted to the base year.
To get the total fuel cycle cost, the net present value NPV was used, which can be expressed as follows: 4. Uncertainty Analysis The unit costs for each of the components in the fuel cycle were applied using an uncertainty analysis by Monte Carlo simulation using Latin Hypercube extraction mode [ 19 ].
It was assumed that the costs of the components would be simulated by triangular distribution. The triangular distribution is a representative nonparametric distribution, which is effective in cases when there is not much data, and the distributions are unknown.
The triangular distribution may appear symmetric, right-skewed, or left-skewed according to the expert opinions. The triangular distribution has a very obvious appeal because it is easy to think about the three defining parameters in a fuel cycle economic analysis and to envisage the effect of any changes. Sensitivity Analysis This study conducted a sensitivity analysis of some unit costs in which the variability is considered large, such as the uranium price, Pyro-UO2 reprocessing, and Pyro-Metal-Fab.
Results and Discussion 5. The relative total costs of the fuel cycle options are presented by the bar chart in Figure 3. Figure 3 shows that the uranium price is the key cost component of the LFCC in all of these four nuclear fuel cycles.
With the current uranium price, the OT is the most economical option and the Pyro-SFR is the second due to the low uranium consumption. In the Pyro-SFR scenario, the uranium consumption decreases because of the utilization of the metal fuel made from the reprocessed TRU.
Generally, two decisions, that is, which kind of reactor to employ and whether or not to deploy a spent fuel treatment technology, mainly determine the direction of the nuclear fuel cycle. Due to the introduction of techniques to treat the PWR spent fuel, the mass flows of nuclear fuel cycles were changed accordingly.
Therefore, it is informative to present the cost share of the spent fuel treatment technique in the LFCC as shown in Figure 4.
After usage in the power plant the spent fuel is delivered to a reprocessing plant if fuel is recycled 2 or to a final repository if no recycling is done 3 for geological disposition. The natural concentration 0. Accordingly UF6 produced from natural uranium sources must be enriched to a higher concentration of the fissionable isotope before being used as nuclear fuel in such reactors.
The level of enrichment for a particular nuclear fuel order is specified by the customer according to the application they will use it for: light-water reactor fuel normally is enriched to 3. Enrichment is accomplished using any of several methods of isotope separation. Gaseous diffusion and gas centrifuge are the commonly used uranium enrichment methods, but new enrichment technologies are currently being developed.
As of there are vast quantities of depleted uranium in storage. The United States Department of Energy alone has , tonnes. Main article: Nuclear fuel For use as nuclear fuel, enriched uranium hexafluoride is converted into uranium dioxide UO2 powder that is then processed into pellet form. The pellets are then fired in a high temperature sintering furnace to create hard, ceramic pellets of enriched uranium.
The cylindrical pellets then undergo a grinding process to achieve a uniform pellet size. The pellets are stacked, according to each nuclear reactor core 's design specifications, into tubes of corrosion-resistant metal alloy.
The tubes are sealed to contain the fuel pellets: these tubes are called fuel rods. The finished fuel rods are grouped in special fuel assemblies that are then used to build up the nuclear fuel core of a power reactor. The alloy used for the tubes depends on the design of the reactor. Stainless steel was used in the past, but most reactors now use a zirconium alloy.
For the most common types of reactors, boiling water reactors BWR and pressurized water reactors PWR , the tubes are assembled into bundles  with the tubes spaced precise distances apart. These bundles are then given a unique identification number, which enables them to be tracked from manufacture through use and into disposal.
Service period[ edit ] Transport of radioactive materials[ edit ] Transport is an integral part of the nuclear fuel cycle. There are nuclear power reactors in operation in several countries but uranium mining is viable in only a few areas. Also, in the course of over forty years of operation by the nuclear industry, a number of specialized facilities have been developed in various locations around the world to provide fuel cycle services and there is a need to transport nuclear materials to and from these facilities.
With some exceptions, nuclear fuel cycle materials are transported in solid form, the exception being uranium hexafluoride UF6 which is considered a gas. Most of the material used in nuclear fuel is transported several times during the cycle. Transports are frequently international, and are often over large distances.
Nuclear materials are generally transported by specialized transport companies. Since nuclear materials are radioactive , it is important to ensure that radiation exposure of those involved in the transport of such materials and of the general public along transport routes is limited. Packaging for nuclear materials includes, where appropriate, shielding to reduce potential radiation exposures.
In the case of some materials, such as fresh uranium fuel assemblies, the radiation levels are negligible and no shielding is required. Other materials, such as spent fuel and high-level waste, are highly radioactive and require special handling. To limit the risk in transporting highly radioactive materials, containers known as spent nuclear fuel shipping casks are used which are designed to maintain integrity under normal transportation conditions and during hypothetical accident conditions.
In-core fuel management[ edit ] A nuclear reactor core is composed of a few hundred "assemblies", arranged in a regular array of cells, each cell being formed by a fuel or control rod surrounded, in most designs, by a moderator and coolant , which is water in most reactors. Because of the fission process that consumes the fuels, the old fuel rods must be replaced periodically with fresh ones this is called a replacement cycle. During a given replacement cycle only some of the assemblies typically one-third are replaced since fuel depletion occurs at different rates at different places within the reactor core.
Furthermore, for efficiency reasons, it is not a good policy to put the new assemblies exactly at the location of the removed ones. Even bundles of the same age will have different burn-up levels due to their previous positions in the core. Thus the available bundles must be arranged in such a way that the yield is maximized, while safety limitations and operational constraints are satisfied. Consequently, reactor operators are faced with the so-called optimal fuel reloading problem, which consists of optimizing the rearrangement of all the assemblies, the old and fresh ones, while still maximizing the reactivity of the reactor core so as to maximise fuel burn-up and minimise fuel-cycle costs.
This is a discrete optimization problem, and computationally infeasible by current combinatorial methods, due to the huge number of permutations and the complexity of each computation.
Many numerical methods have been proposed for solving it and many commercial software packages have been written to support fuel management. This is an ongoing issue in reactor operations as no definitive solution to this problem has been found.
Operators use a combination of computational and empirical techniques to manage this problem. The study of used fuel[ edit ] Main article: Post irradiation examination Used nuclear fuel is studied in Post irradiation examination , where used fuel is examined to know more about the processes that occur in fuel during use, and how these might alter the outcome of an accident.
For example, during normal use, the fuel expands due to thermal expansion, which can cause cracking. Most nuclear fuel is uranium dioxide, which is a cubic solid with a structure similar to that of calcium fluoride. In used fuel the solid state structure of most of the solid remains the same as that of pure cubic uranium dioxide. The solid state structure of uranium dioxide, the oxygen atoms are in green and the uranium atoms in red Uranium dioxide is very insoluble in water, but after oxidation it can be converted to uranium trioxide or another uranium VI compound which is much more soluble.
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