Mechanical behaviour modelling of fractured nuclear fuel pellets

The mechanical behaviour of fractured nuclear fuel pellets is far from simple. In order to take correctly into account this behaviour and model it in the frame of a computer code, a lot of phenomena must be examined. Most of them can hardly be assessed physically and so only empirical models are available.This paper deals with some mechanical and physical phenomena which participate in the total radial deformation of a fuel rod during its in-reactor lifetime and which are mainly relevant to pellet fracturing and pellet-cladding mechanical interaction (PCMI) in normal (steady state) and off-normal (transient) operating situations. Based on qualitative considerations and comparison with experimental results, empirical models for pellet fracturing and PCMI have been established, introduced into the code and calibrated against various experimental results, so that the evolution of fuel radial deformation can be correctly simulated.     

A three-dimensional study of nuclear fuel rod behavior during startup

A three-dimensional finite element study is made of the behavior of cylindrical uranium dioxide fuel pellets during startup. The finite element code uses an eight-noded box element of arbitrary shape to build up the stiffness and stress characteristics by Gaussian integration. Each box has 33 degrees of freedom: 24 corresponding to the three motions at each of the eight nodes; and nine internally eliminated to minimize strain energy. The nine internal degrees of freedom are highly effective in eliminating shear error, and thus permitting far fewer elements than are required when tetrahedron elements are used. The element uses an isoparametric approach, so that the box can have eight arbitrarily positioned nodes. So long as the thermal expansions of the fuel rod can be described by a linear variation in the element, the code takes highly accurate account of it. Plasticity is accounted for by the secant modulus approach. Friction between the pellet and the cladding can be introduced by springs between the relevant finite elements in each area. A feature of the analysis allows cracks to appear in the uranium dioxide fuel as it is heated and the growth of the cracks can be traced as a function of linear power generated in the rod. The code can predict such things as pellet deformations and the stress and strain distributions within the pellets and the cladding. The three-dimensionality of the analysis allows a detailed view of these stresses and strains, and the interaction between the axial and plane stress distributions.     

Self-consistent model of nuclear power and nuclear fuel cycle

Under discussion are such major aspects of the nuclear energy sector as cost effectiveness, nuclear and environmental safety of reactors and nuclear fuel cycle facilities, sustained fuel supply, and proven feasibility of a proliferation-resistant technology. These requirements can be met, for instance, by a two-circuit nuclear facility with an inherently safe fast reactor of the BREST type which is expected to produce electricity at a cost not higher than that at modern LWRs. Fuel supply to such facilities and to a relatively small number of thermal reactors with BR<1, could be provided by fast reactors using depleted uranium as makeup fuel and having a small breeding gain in the core (CBR≈1.05) and bottom blanket (full BR≈1.1). Use of a high-boiling metallic coolant (lead) affords deterministic nuclear, technical and environmental safety of the plants in design-basis and hypothetical accidents. Introduction of a transmutational NFC is viewed as one of the avenues to global environmental safety, when the equivalent activity of long-lived high-level waste is made lower or close to the activity of the source material going into energy production. With such a balance in place, nuclear power could be regarded, in a sense, as waste-free.     

Optimal fuel utilization during decommissioning of nuclear power plants with RBMK reactors

When RBMK reactors are decommissioned successively in the same nuclear power plant, part of the fuel of the stopped reactors can be transferred to other units and additionally burned in continuing operations. The problem of minimizing the consumption of fresh fuel by optimal distribution of the additionally burned fuel over the reactors is examined. The limitations on the refueling rates, the holding time of fuel assemblies prior to transfer, the service life of fuel assemblies, and certain characteristics of reactors are taken into account. It is shown that the reuse of fuel in other units permits saving from one to almost two thousand fresh fuel assemblies and that the effect of optimizing the additional burn regime can reach several hundreds of saved fuel assemblies. __________ Translated from Atomnaya énergiya, Vol. 102, No. 5, pp. 284–290, May, 2007.     

Self-consistent model of nuclear power development and fuel cycle

The use of a high-boiling heat-transfer metal (lead) deterministically ensures sufficient nuclear, engineering, and ecological safety in design and hypothetical accidents. The transmutation nuclear fuel cycle makes global environmental safety closer, when the equivalent activity of the long-lived components of hot waste is lower than, or close to, that of the raw material used. When such equality is reached, nuclear power can be considered to be waste-free, in a sense. A conceptual model envisaging a large-scale, long-term nuclear energy industry is proposed as a solution to the aforementioned problems. Ministry of Atomic Energy of the Russian Federation. NIKIéT (Scientific Research and Design Institute for Power Engineering). Translated from Atomnaya énergiya, Vol. 86, No. 5, pp. 361–370, May, 1999.     

Behavior of uranium-erbium oxide fuel pellets during cyclic heat treatment

The results of studies of the behavior of uranium-erbium fuel pellets during identical repeated heat tests with analysis of the changes of the microstructure, density, geometric dimensions, and resinterability are presented. It is shown that depending on quality some pellets break down in the course of these tests while others remain whole and swell or densify and decrease in size. It was determined that the pellets break down because the erbium oxide distribution in the molding powder and the pellets is nonuniform. Adjustment of the process regime eliminated pellet breakdown during cyclic heat treatment.     

Dry bag isostatic pressing for improved green strength of surrogate nuclear fuel pellets

Dry bag isostatic pressing is proposed for mass production of nuclear fuel pellets. Dry bag isostatically pressed rods of a fuel surrogate (95% CeO₂-5% HfO₂) 200 mm long by 8 mm diameter were cut into pellets using a wire saw. Four different binders and CeO₂ powder obtained from two different sources were investigated. The strength of the isostatically pressed pellets for all binder systems measured by diametral compression was about 50% higher than pellets produced by uniaxial dry pressing at the same pressure. It was proposed that the less uniform density of uniaxially pressed pellets accounted for the lower strength. The strength of pellets containing CeO₂ powder with significantly higher moisture content was five times higher than pellets containing CeO₂ powder with a low moisture content even though they were 25% less dense. Capillary pressure of the moisture was thought to supply the added binding strength.     

Micro-structured nuclear fuel and novel nuclear reactor concepts for advanced power production

Many applications (e.g. terrestrial and space electric power production, naval, underwater and railroad propulsion and auxiliary power for isolated regions) require a compact-high-power electricity source. The development of such a reactor structure necessitates a deeper understanding of fission energy transport and materials behavior in radiation dominated structures. One solution to reduce the greenhouse-gas emissions and delay the catastrophic events' occurrences may be the development of massive nuclear power. The actual basic conceptions in nuclear reactors are at the base of the bottleneck in enhancements. The current nuclear reactors look like high security prisons applied to fission products. The micro-bead heterogeneous fuel mesh gives the fission products the possibility to acquire stable conditions outside the hot zones without spilling, in exchange for advantages – possibility of enhancing the nuclear technology for power production. There is a possibility to accommodate the materials and structures with the phenomenon of interest, the high temperature fission products free fuel with near perfect burning. This feature is important to the future of nuclear power development in order to avoid the nuclear fuel peak, and high price increase due to the immobilization of the fuel in the waste fuel nuclear reactor pools.     

核燃料循环成本与核电的竞争力

国际市场核燃料价格变幻莫测,对我国核电的成本和发展产生影响,本文提出了控制整个核燃料循环成本的设想,以提升中国核电的竞争力,促进核燃料产业和核电产业的共同发展。     

State of and problems in the nuclear power fuel cycle

Conclusions The aim of the INFCE program was not negotiation, but a broad, multisided examination of various aspects of nuclear power development. The studies carried out within the framework of the INFCE did not lead to any unexpected conclusions; however, a thorough analysis of the possibilities and problems of nuclear power at the present time taking account of actual economic, scientific-technical, ecological and other factors, as well as a strengthening of nonproliferation has strengthened the position of nuclear power. Estimates of nuclear demand over the long term and methods of satisfying that demand has shown that these goals can not be confidently attained by any reactor systems or fuel cycles. In particular, for a number of nations having high industrial potential, the combination of fast breeder reactors with light-water reactors is the optimum solution to the problem of long-term satisfaction of energy needs.The work condcuted by the INFCE confirmed the lack of fuel cycles that are proof against proliferation of nuclear weapons, but the work did show that when certain measures are satisfied and effective safeguards implemented, all fuel cycles presently used are sufficiently secure in this respect.Work has been completed on an international evaluation of the nuclear fuel cycle. The editorial board would like to call the reader's attention to an article devoted to general notes and the work of the fifth working group.Translated from Atomnaya Énergiya, Vol. 49, No. 6, pp. 343–349, December, 1980.     

Prevention of fuel rod ballooning in nuclear power plants

Possible means of eliminating ballooning as a mode of failure of fuel rods due to overheating are described. Ballooning tends to block cooling passages and hence render energency cooling inoperative. Means proposed involve altering the shape of the yield locus so that the plastic strain increment vector lies in the axial rather than the circumferential direction of the fuel rod. Proposed changes in yield locus are accomplished by texturing of the zirconium cladding or by grooving or by wrapping the fuel rod.     

核电厂运行人员防人因失误管理

要确保核电厂安全稳定运行,做好设备和人员管理是两项重要工作,本文结合秦山第三核电有限公司在防止人因失误方面的一些尝试,探讨了核电厂运行过程中如何有效控制和防止人因失误方面的思路和构想。     

Analysis of optical density data generated from neutron radiographs of uranium-plutonium mixed oxide fuel pellets inside sealed nuclear fuel pins

A quantitative analysis of neutron radiographs of welded nuclear fuel pins containing uranium-plutonium mixed oxide fuel pellets has been carried out to obtain a simple model for the transmission of neutrons through fuel pins during neutron radiography. The optical density data obtained by detailed microdensitometer scanning across the image of pellets of varying plutonium enrichment has been correlated to the product of the macroscopic neutron cross section and the distance traversed by the neutrons. Based on the experimental data, a simple model which can be applied to fuel pins of different dimensions and plutonium enrichment has been derived.     

展望可再生核电能源取代火电的前景

降低温室效应的有效途径之一为开发核电.为了核电的可持续发展,应开发可再生核能.本文对铀-钚可再生核燃料与钍-铀可再生核燃料的特性进行了阐述与比较,特别强调在我国钍-铀可再生核燃料的应用前景.     

Stability of a nuclear power generation plant with circulating fuel

A nuclear power plant with circulating incompressible fuel is discussed. The active zone of the reactor is idealized by a system with lumped parameters and the heat exchanger by a unit with distributed parameters. The stability of such a plant over a small region of the steady state cycle of operation is demonstrated. For the special case when the importance of delayed neutrons is negligibly small, the stability is demonstrated relative to arbitrary deviations from the equilibrium state.Translated from Atomnaya Énergiya, Vol. 21, No. 1, pp. 3–6, July, 1966.     

Adjoint sensitivity analysis in nuclear reactor fuel behavior modeling

A computer program, SCODE, has been developed for calculating sensitivities for EPRI's SPEAR-ALPHA nuclear fuel performance code FCODE-ALPHA. Eleven critical parameters are assessed for the effects of their independent variations on 33 basic variables in the FCODE-ALPHA model. The enormous wealth of sensitivities that result, consisting of 363 quantities per axial node per time step, are calculated following FCODE-ALPHA computations on each time step. SCODE is based on adjoint sensitivity analysis, which is an analytic technique, obviating the need for numerical differentiation via repeated code runs at varied parameter values. Evaluation of sensitivities is reduced to a problem in linear algebra and is handled by standard matrix manipulations. Compared with the customary numerical differentiation approach, SCODE offers advantages of significant runtime reduction, exactitude of results, and on-line computation of sensitivities.