Increasing fuel burnup in VVER

The results of investigations of fuel burnup increase in VVER are presented. The influence of the costs of different technological stages, changes in the number of refuelings and run time, fuel enrichment and waste, and the consumption of natural uranium on increasing burnup is examined. An analysis taking account of the uncertainty of future prices is performed. The price for natural uranium up to 2020 is estimated using a model. The results presented in this article show that the cost reduction in the fuel component with an increase of VVER fuel burnup in an open fuel cycle can be 6%. __________ Translated from Atomnaya énergiya, Vol. 104, No. 3, pp. 137–141, March, 2008.     

Characterization of simulated burnup fuel by nanoindentation

A simulated burnup UO₂ based fuel (150 GWd/t) was prepared by solid-state reactions. The phase equilibria of the simulated fuel were evaluated by XRD and SEM/EDX analysis. Nanoindentation tests were performed for the simulated fuel at room temperature in air. The modulus and hardness of the matrix phase and oxide precipitates that exit in the simulated fuel were directly evaluated by the nanoindentation.     

VVER nuclear fuel burnup with different absorbers

A computational study is performed of the fuel burnup in VVER-1000 using different absorbers in open and closed fuel cycles. It is shown that mixtures of plutonium isotopes (energy and others) can give the same effect as gadolinium, which is currently used. Fuel burnup increases. When neptunium, americium, and curium isotopes are used as a consumable absorber in a closed fuel cycle, the accompanying effect is elimination of long-lived α-emitting radionuclides which have accumulated in long-term repositories.     

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.     

Improvement of the design of the series-produced fuel element of the VVÉR-440 reactor to increase burnup

Conclusion The fuel elements for the VVÉR-440, which were developed for a 4-yr run, operate satisfactorily to an average burnup of 59 MW-day/kg of uranium in the most-stressed fuel element with average burnup of the unloaded fuel of 40 MW-day/kg. Through the introduction of end beveling of the pellets, the mobility of the fuel column is increased. Furthermore, the presence of bevels makes possible a reduction of the number of chips and elimination of process crumbs, and the high mobility of the fuel column makes it possible, during outfitting of the fuel element, to eliminate the axial gaps between pellets, which are unacceptable for safety reasons. The increase in the initial helium gage pressure has made possible substantial improvement of the thermomechanical characteristics of the fuel elements and avoidance of high fuel temperatures and large gas release. When the conversion is made to a 4-yr fuel run, the number of fuel assemblies refueled each year decreases from 117 to 90 per power-generating unit, natural uranium consumption is reduced by 11–12% [2], zirconium consumption is lowered, and the effective capacity of burned-up fuel stores is increased.I. V. Kurchatov Institute of Atomic Energy. Mashinostroitel'nyi Zavod Production Association. All-Union Scientific Research Institute of Aviation Materials. Translated from Atomnya Énergiya, Vol. 72, No. 2, pp. 121–124, February, 1992.     

Double-strata high burnup fuel performance in light water reactors

This study is aimed at the development of a fuel cycle concept for host countries with a lack of nuclear infrastructure. Two interrelated criteria, proliferation resistance and high-burnup, form the general framework of the fuel management scenario with the highest priority given to light water reactor technology and plutonium-free fresh fuel. Logically it implies the use of uranium oxide with enrichment close to 20%, whose effective utilization forms the main subject of the present paper. A sequence of two irradiation cycles for the same fuel pins in two different light water reactors is the key feature of the advocated approach. It is found that the synergism of PWR and pressure tube graphite reactor offers fuel burnup up to 140 GWd/tHM. Being as large as 8% in the final isotopic vector, the fraction of ²³⁸Pu serves as an inherent protective measure against plutonium proliferation.     

Spent fuel burnup estimation by Cerenkov glow intensity measurement

The Cerenkov glow images from irradiated fuel assemblies of boiling-water reactors (BWR) and pressurized-water reactors (PWR) are generally used for inspections. For this purpose, a new UV-I.I. CVD (ultra-violet light image intensifier Cerenkov viewing device), has been developed. This new device can measure the intensity of the Cerenkov glow from a spent fuel assembly, thus making it possible to estimate the burnup of the fuel assembly by comparing the Cerenkov glow intensity to the reference intensity. The experiment was carried out on BWR spent fuel assemblies and the results show that burnups are estimated within 20% accuracy compared to the declared burnups for the tested spent fuel assemblies for cooling times ranging from 900-2.000 d     

反应率线性外推含钆燃料燃耗计算方法的改进

传统预估-校正方法(Predictor-Corrector Method,PC方法)在采用较大步长进行含钆燃料燃耗计算时会出现显著的误差,为此,日本学者提出了微观反应率线性外推方法(Projected Predictor-Corrector Method,PPC方法),获得明显的改进效果.本文从钆的微观反应率随核子密度...     

High power ramping in commercial PHWR fuel at extended burnup

Argentinean Atucha and Embalse NPP, both PHWR with on line refuelling with approximately 68,000 fuel elements, irradiated at standard burnup, during the refuelling the fuel changes the power close to a mathematical ideal step. Recently, Atucha core started to operate fully with slightly enriched uranium (SEU, 0.85% of enrichment) increasing the burnup more than 50%, thus producing the first irradiated data base of on line refuelling at extended burnup using commercial fuel elements.The BACO code was extensively used in Argentina to model the physical behaviour of both fuel elements, natural UO₂ and SEU. The hoop stress predicted by BACO at the inner surface of the cladding correlate very well with the fuel failure probability over a wide range of tests. Using the data base of present commercial extended burnup fuel, a simple criterion of fuel failure taking into account probabilistic and parametric analysis correlate very well with the present irradiation experience, in agreement with previous BACO experience which confirm the expected behaviour and the SEU fuel element design.     

Metallic fuel for Na-cooled reactors with an extended burnup cycle

In recent years, various reactors and fuel-cycle concepts have been proposed as alternatives to the (Pu-U)O₂ mixed-oxide fuel cycle. This interest has been stimulated by the need to utilize the U resources and also to contribute to the solution of the proliferation problem. To date, essentially all combinations of fuel-cycle mixes have been considered, except the denatured FBR operating on an extended burnup cycle. The basic feature of the proposed concept is a ²³³U²³⁸U LMFBR using metallic fuel, enriched at the beginning of life to about 6 at. % cooled with Na, and designed to operate in such a way that, once the reactor is built, it only needs natural or depleted U as feed for the rest of the life of the reactor. The denatured breeder simply enriches the U to the level necessary to maintain criticality. Calculations show that the reactivity swing over each refueling interval, the fuel-pin performance and some safety parameters are all within current technology constraints.     

Interaction of uranium-molybdenum fuel with an aluminum matrix with deep burnup

A thermodynamic analysis is used to calculate the phase and component composition of uraniummolybdenum fuel with burnup 200 GW·days/ton. The equilibrium composition of the gas phase, consisting mainly of gaseous cesium whose pressure reaches 30 kPa, is determined more accurately. The quantitative composition of the phase of solid solutions of tellurides, whose formation degrades the structure of a fuel granule, is presented. Thermal tests of the fuel composition (U–Mo)–Al were performed. The investigation was performed in the presence of simulators of the chemically active fission products of cesium and iodine at different temperature. The interaction zone of (U–Mo)–Al is investigated by means of metallography and scanning electron microscopy. The data obtained on the composition of the indicated zone made it possible to conjecture the character of interaction between the fuel material and the aluminum matrix.     

Effect of fuel burnup on the effectiveness of ultrasonic detection of leaky fuel elements in VVER-1000 fuel assemblies

The effect of fuel burnup in VVER-1000 fuel elements on the utilization effectiveness of ultrasonic detection of leaky fuel elements is examined. It is determined that the limitations of this method are due to the interaction of fuel-element cladding with the fuel pellets. Threshold for fuel burnup in VVER-1000 fuel elements with E-110 alloy cladding, determining the application limits of ultrasonic detection of leaky fuel elements in fuel assemblies, is determined.     

Numerical simulation of mixed oxide fuel burnup taking account of double heterogeneity

The results of a numerical simulation of the burnup of mixed oxide fuel in VVER-1000 taking account of double heterogeneity are presented. The fuel consists of two different materials: a depleted uranium matrix with small amounts of plutonium and agglomerates consisting of particles with an elevated plutonium concentration. An important problem is taking double heterogeneity into account correctly, making it possible to evaluate the ratio of the energy release over the fuel-element pellet. Numerical results are obtained for the burnup distribution, energy release, and the concentrations of helium, krypton, and xenon over the radial zones of a fuel element depending on the average fuel burnup over the pellet. The MCU-REA program with the ORIMCU module for calculating burnup was used to perform the calculations.