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.     

High-enrichment fuel in VVER

The results of a search for the optimal water-uranium ratio for VVER with no changes to the fuel elements and assemblies are presented. It is shown that decreasing the volume of a fuel pellet while maintaining the same ²³⁵U load as a result of increasing the enrichment will decrease the specific consumption of uranium and increase the run time. The proposed modifications to the fuel can be implemented in operating reactors and advanced VVER designs.     

Study of VVER fuel with dopant additives

This is a report of a study of the effect of alloy additives on the properties of fuel under conditions typical of water cooled reactors. The behavior of uranium oxide fuel with added mixtures of the oxides of aluminum, silicon, niobium, and iron during reactor irradiation of experimental fuel elements is investigated in the MIR research reactor. The feasibility of using aluminum-silicate additives for improving the operating characteristics of fuel pellets under reactor irradiation conditions is demonstrated. Translated From Atomnaya énergiya, Vol. 105, No. 4, Pp. 205–210, October, 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.     

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.     

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.     

Magnetic gamma spectrometer determination of fuel element burnup

The article proposes the use of a magnetic Compton spectrometer to determine fuel element burnup nondestructively. Burnup is determined from the intensity of the fission product gamma lines. One of the gamma lines useful for this purpose is the Nd¹⁴⁴ line, E = 2.19 MeV, whose rate of intensity decay as determined by the half-life of Ce¹⁴⁴ is 284 days.The authors welcome this opportunity to express their heartfelt gratitude to P. I. Saukov and to Yu. F. Chernilin and the staff serving the IRT reactor for their kind and invaluable assistance in performance of this work.     

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.     

Current trends in fuel development and future needs in extended burnup

In this paper, the status of fuel development programs for light water commercial reactors is reviewed. New fuel designs for extended burnup fuel cycles are considered along with the current emphasis on increasing the reliability of commercial fuel. The needs for fuel performance modeling in support of extended burnup and higher reliability are summarized.     

Method for detecting unsealed fuel elements in VVER and RBMK fuel assemblies and test results

A method is described for detecting unsealed fuel elements in VVER and RBMK fuel assemblies in a cooling pond. The method is based on detecting water which has seeped under the cladding of an unsealed fuel element. The results of testing the method on unsealed VVER-440, -1000, and RBMK-1000 fuel assemblies are presented. Translated from Atomnaya énergiya, Vol. 106, No. 2, pp. 84–88, February, 2009.     

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     

Numerical modeling of the temperature distribution in a VVER fuel element

The temperature distribution in a VVER fuel element with deep burnup of nuclear fuel is studied. Numerical and analytical methods are used. It is shown that a stationary temperature distribution is established in no longer than 1 min. Analytical methods are used to obtain the temperature dependence of the radius of a fuel element in a stationary regime     

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...     

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.     

MIR reactor tests of VVER fuel elements in cyclic power variation regimes

Tests of prefabricated VVER fuel elements burnup 50–60 MW·days/kg in regimes with cyclic power variation have been performed in a circuit setup of the MIR research reactor. The testing procedures are described, and the designs of the irradiation setups are presented. Some fuel elements are equipped with sensors for performing in-reactor measurements, which yielded the experimental data on the variation of the fuel element parameters during the tests (gas pressure, fuel temperature, length). Some results of post-reactor materials-engineering investigations are presented. All fuel elements remained airtight. __________ Translated from Atomnaya énergiya, Vol. 104, No. 2, pp. 80–84, February, 2008.     

Recommended strategy and limitations of burnable absorbers used in VVER fuel assemblies

There is an obvious effort to increase the burn up of used fuel assemblies in order to improve fuel utilization.A more effective operation can be realized by extending the fuel cycles or by increasing the number of reloadings.This change is nevertheless connected with increasing the uranium enrichment even above 5% of 235 U. Burnable absorbers are widely used to compensate for the positive reactivity of fresh fuel. With proper optimization, burnable absorbers decrease the reactivity excess at the beginning of the cycle, and they can help with stabilization of power distribution. This paper describes properties of several materials that can be used as burnable absorbers. The change in concentration or position of the pin with a burnable absorber in a fuel assembly was analyzed by the HELIOS transport lattice code. The multiplication factor and power peaking factor dependence on fuel burn up were used to evaluate the neutronic properties of burnable absorbers. The following four different materials are discussed in this paper: Gd_2O_3, IFBA, Er_2O_3,and Dy_2O_3.Gadolinium had the greatest influence on fuel characteristics. The number of pins with a burnable absorber was limited in the VVER-440 fuel assembly to six. In the VVER-1000 fuel assembly, 36 pins with a burnable absorber can be used as the assembly is larger. The erbium depletion rate was comparable with uranium burn up.Dysprosium had the largest parasitic absorption after depletion.