Nuclear fuel management via fuel quality factor averaging

The numerical procedure of prime number averaging is applied to the fuel quality factor distribution of once- and twice-burned fuel in order to evolve a fuel management scheme. The resulting fuel shuffling arrangement produces a near optimal flat power profile both under beginning-of-life and end-of-life conditions. The procedure is easily applied requiring only the solution of linear algebraic equations.     

Nuclear fuel in the shelter

The stages of multiyear investigations of the fuel-containing materials remaining in the Shelter after the accident at the Chernobyl nuclear power plant, including the determination of their total amount and the physicochemical properties, are described. Thus far ∼150 tons of fuel from the destroyed reactor have been found inside the Shelter. Another ∼ 30 tons could be located in sites which are still inaccessible to investigators. One section of this paper is devoted to the analysis of the possibility of the decomposition of the lava-like fuel-containing materials during a long storage period (ten years) after the Shelter is converted into an ecologically safe system. Questions concerning the development of a system for monitoring fuel-containing materials are discussed. __________ Translated from Atomnaya énergiya, Vol. 100, No. 4, pp. 258–267, April, 2006.     

Nuclear fuel considerations for the 21 century

There are many external influences that may control the path that nuclear power deployment follows. In the next 50 years several events may unfold. Fear of the consequences of the greenhouse effect may produce a carbon tax that would make nuclear power economically superior very quickly. This, in turn, would increase the rate at which uranium reserves diminish due to the increased rate of nuclear power deployment. However, breakthroughs in the extraction of uranium from the sea or deployment of fast breeder reactors would greatly extend the uranium reserves and, as well, utilize the thorium cycle.On the other hand, carbon sequestering technology breakthroughs could keep fossil fuels dominant for the remainder of the century. Nuclear power may only then continue, as today, in a lesser role or even diminish. Fusion power or new developments in solar power could completely displace nuclear power as we know it today.Even more difficult to predict is when the demand for mobile fuel for transportation will develop such that hydrogen and hydrogen rich fuel cells will be in common use. When this happens, nuclear power may be the energy source of choice to produce this fuel from water or methane. In a similar vein, the demand for potable and irrigation water may be another driver for the advent of increased deployment of nuclear power.With all these possibilities of events that could happen it appears impossible to predict with any certainty which path nuclear power deployment may take. However, it is necessary to define a strategy that is flexible enough to insure that when a technology is needed, it is ready to be deployed.For the next few decades there will be an evolutionary improvement in the performance of uranium oxide and mixed uranium oxide-plutonium oxide (MOX) LWR fuels. These improvements will be market driven to keep the cost of fuel and the resulting cost of nuclear power electricity as competitive as possible. The development of fuels for accelerator transmutation and for reactor transmutation with inert matrix fuels is in its infancy. A great deal of research has been initiated in a number of countries, which has been summarized in recent conferences. In Europe the work on these fuels is directed at the same problem as their utilization of MOX; namely to reduce the inventory of separated plutonium, minor actinides, and Long Lived Fission Products (LLFP). In the United States there is no reprocessing and thus no inventory of separated civilian plutonium. However, in the United States there is a resistance to a permanent spent fuel repository and thus accelerator transmutation presents a possible alternative. If nuclear power does have a long-term future, then the introduction of the fast reactor is inevitable. Included in the mission of the fast reactors would be the elimination of the inventory of separated plutonium while generating useful energy. The work that is ongoing now on the development of fuel concepts for assemblies that contain actinides and LLFP would be useful for fast reactor transmutation.There is still a great deal of work required to bring the fast breeder reactor option to maturity. Fortunately there is perhaps a fifty-year period to accomplish this work before fast breeders are necessary. With regard to fast reactor fuel development, future work should be considered in three stages. First, all the information obtained over the past forty years of fast reactor fuel development should be completely documented in a manner that future generations can readily retrieve and utilize the information. Fast reactor development came to such an abrupt halt world-wide that a great deal of information is in danger of being lost because most of the researchers and facilities are rapidly disappearing. Secondly, for all of the existing fast reactor fuels, and this includes, oxides, carbides, nitrides, and metallic fuels, the evolutionary work was far from being completed. Although mixed oxide fuels were probably the furthest advanced, there were many concepts for improved claddings and advanced fabrication methods that were never fully explored. Finally, with such an extended period before fast reactors are needed there is ample time for truly innovative fuels to be developed that are capable of performing over a wide range of conditions and coolants.     

Nuclear fuel pellet inspection using artificial neural networks

Nuclear fuel must be of high quality before being placed into service in a reactor. Fuel vendors currently use manual inspection for quality control of fabricated nuclear fuel pellets. In order to reduce workers' exposure to radiation and increase the inspection accuracy and speed, the feasibility of automation of fuel pellet inspection using artificial neural networks (ANNs) is studied in this paper. Three kinds of neural network architectures are examined for evaluation of the ANN performance in proper classification of good versus bad pellets. Two supervised neural networks, backpropagation and fuzzy ARTMAP, and one unsupervised neural network called ART2-A are applied. The results indicate that a supervised ANN with adequate training can achieve a high success rate in classification of fuel pellets.     

Nuclear fuel cycle strategies including Partitioning and Transmutation

The widespread concern about radioactive waste management has promoted interest during the last decade for the potential role of Partitioning and Transmutation strategies, in order to alleviate the burden on future deep geological repositories. The physics of transmutation allows to point-out preferential approaches, e.g., based on the use of a fast neutron spectrum. The practical implementation of Partitioning and Transmutation implies the development of sophisticated technologies and can be more realistic if seen in a regional context. Some examples will be given to illustrate the “regional” approach, and some considerations will be made on the use of Accelerator Driven Systems (ADS), in the frame of a progressive strategy from present nuclear power fleets to future systems, as studied, e.g., in the frame of the GENERATION-IV initiative.     

Nuclear and materials aspects of the thorium fuel cycle

This paper is an attempt to assess and review the materials aspects of the thorium fuel cycle. It starts with an examination of the nuclear aspects of the thorium fuel cycle, meant as an introduction for materials scientists and engineers who may not normally be familiar with the concepts and terms involved. After defining and describing the thorium and uranium fuel cycles, the reasons for the resurgence of interest in the thorium fuel cycle and the technical and economic considerations that support its early adoption are examined. The reactor physics and fissile economics aspects of the thorium and uranium cycles are then compared. The specific reactor types suitable for the adoption of the thorium cycle are briefly examined and described. Subsequent sections of the paper are devoted to a detailed discussion of the materials aspects of the thorium fuel cycle. Available information on fabrication, refabrication and irradiation performance of thorium-based fuels for light water reactors, heavy water reactors, high temperature gas-cooled reactors, molten salt breeder reactors and fast breeder reactors is critically reviewed and analysed. Materials problems related to cladding and structural materials are also discussed whenever these are unique to the thorium cycle.     

Nuclear proliferation-resistance and safeguards for future nuclear fuel cycle

Corresponding to the world nuclear security concerns, future nuclear fuel cycle (NFC) should have high proliferation-resistance (PR) and physical protection (PP), while promotion of the peaceful use of the nuclear energy must not be inhibited. In order to accomplish nuclear non-proliferation from NFC, a few models of the well-PR systems should be developed so that international community can recognize them as worldwide norms. To find a good balance of ‘safeguard-ability (so-called extrinsic measure or institutional barrier)’ and ‘impede-ability (intrinsic feature or technical barrier)’ will come to be essential for NFC designers to optimize civilian nuclear technology with nuclear non-proliferation, although the advanced safeguards with high detectability can still play a dominant role for PR in the states complying with full institutional controls. Accomplishment of such goal in a good economic efficiency is a future key challenge.     

Nuclear fuel loading pattern optimisation using a neural network

An algorithm to optimise the fuel loading pattern (LP) in nuclear reactors was developed using an artificial neural network (ANN) to generate arrangements for the fuel in the core. The core parameters were calculated with the WIMS-D4 and CITATION-LDI2 codes, and the minimization of the maximum power peaking factor (FP_max) was used to choose the best arrangements. To verify the algorithm a PWR reactor with approximately 1/3 reprocessed fuel loaded was considered. The neutronic performance of the obtained arrangements and the efficiency of the implemented method were analysed. Several configurations were found for the core presenting better characteristics than the reference configuration adopted, so indicating the viability of the developed methodology. The algorithm was applied to a core considering part of the loading with reprocessed fuels, however this technique can be used for standard loadings.     

Nuclear burning wave in fast reactor with mixed Th-U fuel

The possibility of creating a self-sustained regime of a running nuclear burning wave in the critical fast reactor with the mixed Th-U fuel is demonstrated. The calculations were performed in the deterministic approach based on solving the non-stationary multi-group diffusion equation of neutron transport together with the set of equations of the fuel component burn-up and the nuclear kinetics of precursor nuclei of delayed neutrons. The presence of the constructional material Fe and the coolant (the Pb-Bi eutectic) in the reactor composition is taken into account. The calculation results of the space-time evolution of neutron flux and fuel component concentrations are presented for different values of the Th-U ratio in the fuel. The calculations show the remarkable stability of the nuclear burning wave regime against neutron flux distortions in the reactor, which is a result of the negative feedback on reactivity inherent to this regime. This is one of the most important features of the reactor of this type, which ensures its intrinsic safety.     

Nuclear power plant operational diagnostics and control

Before the end of the present century, a significant proportion of the world's needs for electrical energy will be supplied by nuclear power plant. The capital invested in these stations, as opposed to their operating costs, will be considerable. For this reason and to ensure their optimal and safe operation, both as individual units and in a generating network, computer based on-line monitoring, identification and control techniques will be associated with each nuclear plant.     

A metallic fuel cycle for Self-Consistent Nuclear Energy System (SCNES)

A fast reactor core and fuel cycle concept has been discussed for Self-Consistent Nuclear Energy System (SCNES) concept. This paper discussed loading material candidates for long-lived fission products (LLFPs) and removal of stable nuclides from radioactive nuclides with isotope separation using tunable laser. Some of LLFPs were possible to be loaded in metal of the generated form. The potential for LLFP-confinement in the reactor system is discussed along with a metallic fuel cycle concept. The proposed fuel cycle scheme is a successful candidate for SCNES concept.     

The fuel assembly of the 5 MWt Nuclear Heating Reactor

The design principle and main structure of the 5 MW_t Nuclear Heating Reactor are introduced in this article. Also, the design characteristics of the fuel assemblies in mechanical, nuclear and thermal-hydraulic aspects are elucidated.     

A metal fuel fast reactor core for the Self-Consistent Nuclear Energy System

Feasibility of transmutation of the major long-lived FPs (I, Pd, Tc, Sn, Se, Zr, Cs) while maintaining fuel breeding capability for the Self-Consistent Nuclear Energy System is evaluated based on the actinide recycle metal fuel core of a fast reactor. It is shown that I, Pd, Tc, Sn, Se, and Zr can be transmuted simultaneously by an aid of the isotope separation of Pd-107, Zr-93, Sn-126 and Se-79. Cs, which is difficult to transmute with the other FPs, is planned to be utilized as an in-reactor shielding material to confine in the system The overall assessment based on those results indicates that the developed system has the great potential toward the Self-Consistent Nuclear Energy System.     

Dependence of control rod worth on fuel burnup

One important parameter in the design and the analysis of a nuclear reactor core is the reactivity worth of the control rods, i.e. their efficiency to absorb excess reactivity. The control rod worth is affected by parameters such as the fuel burnup in the rod vicinity, the Xe concentration in the core, the operational time of the rod and its position in the core. In the present work, two different computational approaches, a deterministic and a stochastic one, were used for the determination of the rods worth dependence on the fuel burnup level and the Xe concentration level in a conceptual, symmetric reactor core, based on the MTR fuel assemblies used in the Greek Research Reactor (GRR-1). For the deterministic approach the neutronics code system composed by the SCALE modules NITAWL and XSDRN and the diffusion code CITATION was used, while for the stochastic one the Monte Carlo code TRIPOLI was applied. The study showed that when Xe is present in the core, the rods worth is significantly reduced, while the rod worth variation with increasing burnup depends on the rods position in the core grid. The rod worth obtained with the use of the Monte Carlo code is higher than the one obtained from the deterministic code.     

Nuclear plant mix with minimum natural fuel requirement: An optimum theory approach

The optimization of nuclear plant mix is posed as an optimal control problem albeit with some non-standard features. The minimum principle is extended and applied to determien the optimal combination of different reactor types in meeting a given nuclear capacity demand such that the natural fuel requirement is minimum. The optimal policy combines an initial boundary arc along which the reactor type with the highest net breedign gain is installed and a terminal interior arc along which there is no external fuel purchase. The terminal arc is not unique and this enables us to introduce other criteria such as capital cost differential or least breeder installation. Numerical results as well as analytic formulae for the optimal switching times are given for different mix systems. The optimal trade-offs between system parameters and the potential saving in fuel requirement are readily found in a straightforward manner.     

Nuclear reactor control by an asymmetric regulating system

Conclusions An asymmetric regulating system with scattered data units and regulating rods stabilizes an energy distribution which with no external feedback would be essentially unstable. However, with a system of reactor control constructed solely on the basis of an asymmetric regulator, the quality of the transient processes is unsatisfactory with regard to the regulating time, the character of the process, and the maintenance of the mean reactor output.The quality of the transient processes is improved by the use of a combined regulating system which includes a mean output regulator and an asymmetric regulator with an appropriate choice of parameters. But the efficiency of such a system is noticeably inferior to that of a control system constructed on the principle of local regulation. For example, if the same perturbation applied to a combined system is applied to a system of local regulators, it is found that the perturbation is localized, the transient time of the process is one and a half times shorter, and the amplitude of the maximum deviation of the neutron flux is reduced by approximately an order of magnitude compared to that for the combined system. Another defect of the system is that when a breakdown of the mean output regulator occurs, the asymmetric regulator remaining in operation causes positive feedback, and under these conditions may induce an uncontrolled power excursion.A subsequent search for optimal regulating systems evidently may be based on local regulators made partly asymmetric by choosing an appropriate distribution of data and regulating units.Translated from Atomnaya Énergiya, Vol. 46, No. 2, pp. 82–87, February, 1979.     

Nuclear fuel and the characteristics of aerosol formation in the object “Cover”

High-temperature atomization of materials, transfer of elements into the gas phase and the condensation of the elements, occurred during the active stage of the accident at least at a local point of the reactor. As a result of these processes, in some cases the ratio Pu/U in large spherical particles of the dispersed phase differ substantially from the ratio characteristic for the average nuclear fuel in the fourth power generating unit of the Chernobyl nuclear power plant. Therefore, the term “average nuclear fuel” with respect to materials containing nuclear fuel in the object “Cover” is inadequate. Moscow Technological Center “Cover,” Ukrainian Academy of Sciences. Yu. N. Lobach Science Center “Institute of Nuclear Research,” Ukrainian Academy of Sciences. Translated from Atomnaya énergiya, Vol. 82, No 1, pp. 39–44, January, 1997     

采用哑棒修复燃料组件的核特性分析方法及其工程应用

在核电厂正常运行过程中,由于一回路杂物的存在或燃料操作失误,出现了少量燃料棒损伤的情况,通过采用哑棒替换损伤燃料棒可修复损伤燃料组件并回堆使用,可避免降低核电厂运行经济性。本文通过模拟采用不锈钢和锆合金哑棒替换破损燃料棒对燃料组件进行修复,分析修复后燃料组件中子学特性及修复燃料组件对堆芯运行核特性参数的影响机理,评估采用哑棒修复燃料组件并回堆使用对堆芯运行安全的影响,对采用哑棒修复燃料组件建立了完整的核设计分析方法和流程。该方法对采用哑棒修复燃料组件的核设计分析具有广泛的适用性,对采用修复燃料组件的堆芯换料设计具有实际的指导意义。该分析方法和流程的建立在国内反应堆物理分析领域尚属首次,目前该技术已应用于恰希玛一期核电厂堆芯换料设计的工程实践。