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1.
Gadolinium (Gd), in the form of gadolinia (Gd2O3), has been used as integral burnable absorber to UO2 fuel by different companies. Recently, alternative burnable absorber materials are under investigation. In this paper, the results of the study on the use of boron mixed in UO2 as an integral burnable absorber are presented. Boron nitride was selected as the form of B to be added to UO2 fuel based on the stability of B during sintering. Fuel performance analysis code FRAPCON-UNI, which is based on FRAPCON code and has the modifications for boron and helium generation and gasses release models, was used for the calculation of fuel performance. Helium generation was calculated using a model and the result was verified against ORIGEN calculation results. Gas release calculation was based on Forsberg Massih model and different characteristics of the gasses were considered. Power histories of maximum burnup rods (B rod, no B rod, and Gd rod) were selected from reactor physics data. The results indicated significant increases in rod internal pressure by 500 ppm boron addition at the end of life with minimum influence of a grain boundary boron fraction due to high diffusivity of helium and nitrogen. 相似文献
2.
The incorporation of gadolinium directly into nuclear fuel is important regarding reactivity compensation, which enables longer fuel cycles. The incorporation of Gd2O3 powder directly into the UO2 powder by dry mechanical blending is the most attractive process, because of its simplicity. Nevertheless, processing by this method leads to difficulties while obtaining sintered pellets with the minimum required density. This is due to the bad sintering behavior of the UO2-Gd2O3 mixed fuel, which shows a blockage in the sintering process that hinder the densification process. Minimal information exists regarding the possible mechanisms for this blockage and this is restricted to the hypothesis based on the formation of a low diffusivity Gd rich (U,Gd)O2 phase. The objective of this investigation was to study the phase formation in this system, thus contributing to clarifying the causes of the blockage. Experimental evidence indicated the existence of phases in the (U,Gd)O2 system that revealed structures different from the fluorite-type UO2 structure. These phases appear to be isostructural to the phases observed in the rare earth-oxygen system. 相似文献
3.
Masaki Amaya Mutsumi Hirai Hiroshi SakuraiKenichi Ito Masana Sasaki Terumitsu Nomata Katsuichiro KamimuraRyo Iwasaki 《Journal of Nuclear Materials》2002,300(1):57-64
Thermal diffusivities of UO2 and (U, Gd)O2 pellets irradiated in a commercial reactor (maximum burnups: 60 GWd/t for UO2 and 50 GWd/t for (U, Gd)O2) were measured up to about 2000 K by using a laser flash method. The thermal diffusivities of irradiated UO2 and (U, Gd)O2 pellets showed hysteresis phenomena: the thermal diffusivities of irradiated pellets began to recover above 750 K and almost completely recovered after annealing above 1400 K. The thermal diffusivities after recovery were close to those of simulated soluble fission products (FPs)-doped UO2 and (U, Gd)O2 pellets, which corresponded with the recovery behaviors of irradiation defects for UO2 and (U, Gd)O2 pellets. The thermal conductivities for irradiated UO2 and (U, Gd)O2 pellets were evaluated from measured thermal diffusivities, specific heat capacities of unirradiated UO2 pellets and measured sample densities. The difference in relative thermal conductivities between irradiated UO2 and (U, Gd)O2 pellets tended to become insignificant with increasing burnups of samples. 相似文献
4.
An efficient and a practical genetic algorithm (GA) tool was developed and applied successfully to Burnable Poison (BP) placement optimization problem in the reference Three Mile Island-1 (TMI-1) core. Core BP optimization problem means developing a BP loading map for a given core loading pattern that minimizes the total Gadolinium (Gd) amount in the core without violating any design constraints. The number of UO2/Gd2O3 pins and Gd2O3 concentrations for each fresh fuel location in the core are the decision variables. The objective function was to minimize the total amount of Gd in the core together with the residual Gd reactivity binding at the End-of-Cycle (EOC). The constraints are to keep the maximum peak pin power during the core depletion and soluble boron (SOB) concentration at the Beginning of Cycle (BOC) both less than their limit values. The innovation of this study was to search all of the possible UO2/Gd2O3 fuel assembly designs with variable number of UO2/Gd2O3 fuel pins and concentration of Gd2O3 in the overall decision space. The use of different fitness functions guided the solution towards desired (good solutions) region in the solution space, which accelerated the GA solution. The main objective of this study was to develop a practical and efficient GA tool and to apply this tool to designing an optimum BP pattern for a given core loading. 相似文献
5.
《Journal of Nuclear Science and Technology》2013,50(8):449-453
Abstract An analytical method for determining Gd impurity in high purity Eu2O3 is proposed, which makes use of neutron activation and cation-exchange separation to examine its suitability as target material for the production of 152 m, 152, 154Eu. Long-term irradiation of an Eu sample resulted in 153Gd activity amounting to 1.8 times that of the same nuclide produced from an equal quantity of Gd by (n, γ) reaction. This experimental value is quite consistent with that obtained by calculation under the assumption that the 163Gd results from nuclear reaction on 151Eu induced by secondary neutrons. For the accurate determination of Gd, Gd impurity was separated from the Eu sample prior to neutron irradiation in order to reduce the self-shielding effect in the Eu sample. Separation by cation-exchange with α-hydroxyisobutyrate (0.33 M, pH 3.77) made it possible to reduce the content of Eu in the Gd fraction below 7×10?3%. This sufficed to assure that the 159Gd content in 152mEu was smaller than 1×10?3%. For the determination of Gd content below 104 ppm, however, should necessitate further purification of the irradiated Gd fraction. 相似文献
6.
《Journal of Nuclear Materials》2001,288(2-3):92-99
A mixture of UO2 and Gd2O3 powders was pressed into compacts and sintered under various atmospheres ranging from reducing to oxidizing gases. The sintered density of UO2–10 wt% Gd2O3 pellets decreases with increasing oxygen potential of the sintering atmosphere. Dilatometry and X-ray diffraction studies indicate that the delay of densification takes place between 1300°C and 1500°C, along with the formation of (U,Gd) O2. A very large solubility of Gd2O3 in UO2 relative to the reverse solubility might cause Gd ions to diffuse into UO2 so directionally that new pores are produced at the places of Gd2O3 particles. The new pores may be difficult to shrink and thus lead to the density decrease under an oxidizing atmosphere but not under a reducing atmosphere, because a driving force for the shrinkage of new pores may be smaller under an oxidizing atmosphere than under a reducing atmosphere. 相似文献
7.
Utilities operating LWRs require fuel assemblies and in-core fuel management service, which ensure safe, flexible and cost-effective production of electricity. Because the reliability of the fuel has always been the most important requirement, advanced measures to minimize fuel cycle costs are receiving increasing attention in the light of the pressure on costs within the deregulated power generation markets. The role of in-core fuel management in supporting the goal to minimize fuel cycle costs consists in the development of more demanding core loading strategies, i.e. in the first place, more advanced low leakage loading patterns. A prerequisite for this type of loading pattern is the use of an optimized burnable absorber design. Gadolinia (Gd) as integrated burnable absorber is a very effective means for limiting the critical boron concentration and power peaking factors. Current development efforts for optimizing Gd-fuel are focused on the reduction of the inherent penalties of today's Gd-FA designs, i.e. reduced average fuel assembly (FA) enrichment and heavy metal content, as well as the residual reactivity binding. The most effective way to overcome these drawbacks is the reduction of the Gd2O3 concentration to values of ≈2 w/o, for which, according to recent measurements of the heat conductivity of modern Gd-fuels, the reduction of the fissile content in the Gd-rods is no longer necessary. Various feasibility studies have been performed to evaluate the consequences of FA designs with low Gd-concentrations (low-Gd designs) for Siemens PWRs and non-Siemens PWRs, for which more restrictive boundary conditions with respect to critical boron concentration and peaking factors have to be fulfilled. These studies, as well as operation experience of reactor cycles using low Gd-FA reload designs, confirm that the in-core fuel management can handle the different Gd burnout characteristics without problems. The economical benefits of low-Gd designs compared to conventional Gd designs are comparable to those achievable by distinctly more costly and complex alternatives, like the use of enriched gadolinia. 相似文献
8.
《Journal of Nuclear Science and Technology》2013,50(8):608-616
The compatibility of Eu3O3 and (Eu,Gd) 2O3 mixed oxides which contain 0, 1, 5, 10, 50 and 100 mol% of Gd2O3, with type 316 stainless steel was examined by out-of-pile heatings. The heating temperature ranged from 550 to 1,000°C and heating time from 500 h to up to 5,000 h. Metallographic examinations of the stainless steel indicated that chemical reaction between Eu2O3 and stainless steel occurred at 650°C and that grain boundary penetration extended up to 40 μ m after heating at 1,000°C for 500 h. The penetration depth Δ was expressed as a function of heating temperature T as Δ = 3.08 × 104 exp(?1.72 × 102RT) where R is the gas constant and the activation energy is given in cal/mol. Electron probe microanalysis and X-ray diffraction analysis indicated that main reaction product is europium silicate. When Gd, which is a decay product of Eu, is mixed with Eu2O3, the degree of reaction between (Eu,Gd) 2O3 and stainless steel decreases as increase in concentration of Gd2O3. It was found that actually no grain boundary attack was observed even after heating at 1,000°C for 500 h when concentration of Gd2O3;i in (Eu,Gd) 2O3 exceeded 10 Discussion was made of reaction mechanism of Eu2O3 and (Eu,Gd) 2O3 with stainless steel. 相似文献
9.
S. Prucnal A. Wójtowicz K. Pyszniak A. Drozdziel J. Zuk M. Turek L. Rebohle W. Skorupa 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(8-9):1311-1313
When amorphous SiO2 films are bombarded with energetic ions, various types of defects are created as a consequence of ion-solid interaction (peroxy radicals POR, oxygen deficient centres (ODC), non-bridging oxygen hole centres (NBOHC), E′ centres, etc.). The intensity of the electroluminescence (EL) from oxygen deficiency centres at 2.7 eV, non-bridging oxygen hole centres at 1.9 eV and defect centres with emission at 2.07 eV can be easily modified by the ion implantation of the different elements (H, N, O) into the completely processed MOSLED structure. Nitrogen implanted into the SiO2:Gd layer reduces the concentration of the ODC and NBOHC while the doping of the oxygen increases the EL intensity observed from POR defect and NBOHC. Moreover, after oxygen or hydrogen implantation into the SiO2:Ge structure fourfold or fifth fold increase of the germanium related EL intensity was observed. 相似文献
10.
L. Pagano Jr. G.P. Valena S.L. Silva A.E.L. Cludio F.F. Ivashita R. Barco S.N. de Medeiros A. Paesano Jr. 《Journal of Nuclear Materials》2008,378(1):25-29
Samples of UO2and up to 10 wt% of Gd2O3 were prepared by solid-state reaction under a reducing atmosphere, in a thermal path comprising ramps and dwell times in the temperature range of 900–1750 °C. The sintered material was analyzed by X-ray diffraction and 155Gd Mössbauer spectroscopy. The results showed that for samples annealed up to 900 °C, the gadolinium sesquioxide remained unreacted. However, when the temperature was increased to 1300 °C, a solid-state reaction took place forming mixed oxides. For the more severe sintering condition, at 1750 °C, gadolinia left urania partially unreacted producing a material consisting of two compositions, UO2 (with no dissolved gadolinium) and (U, Gd)O2. The proposed heating cycle provided pellets free from Gd2O3 phase and may be used by the nuclear fuel industry as a suitable sintering process. 相似文献
11.
A. Meftah W. AssmannN. Khalfaoui J.P. StoquertF. Studer M. ToulemondeC. Trautmann K.-O. Voss 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(9):955-958
The results of present paper have shown that sputtering of yttrium iron garnet (Y3Fe5O12) under swift heavy ions in the electronic energy loss regime is non-stoichiometric. Here we are presenting additional experimental results for gadolinium gallium garnet (Gd3Ga5O12) as target. The irradiations were performed with different ions (50Cr (589 MeV), 86Kr (195 MeV) and 181Ta (400 MeV)) impinging perpendicularly to the surface. As earlier, the sputtering yield was determined by collecting the emitted gadolinium and gallium atoms on a thin aluminium foil, placed upstream above the target and analyzing the Al catcher by Rutherford backscattering. Also for Gd3Ga5O12, the emission of Gd and Ga is non-stoichiometric. Sputtering appears above a critical electronic stopping power of Sth = 11.6 ± 1.5 keV/nm, which is larger than the threshold for track formation, in agreement with other amorphisable materials. In addition, the angular distribution of the sputtered species was measured for Y3Fe5O12 and Gd3Ga5O12 using 200 MeV Au ions impinging the surface at 20° relatively to the surface. For the two garnets the ratio of Y/Fe (and Gd/Ga) varies with the angle of emitted species and the stoichiometry seems to be preserved only for an emission perpendicular to the surface. 相似文献
12.
《Journal of Nuclear Science and Technology》2013,50(10):1119-1129
Destructive analyses for five spent fuel samples taken from a Gd bearing fuel assembly were done. The measured amounts of actinides of 234-238U, 237Np, 238-242pu 241,242m,243Am 242,244Cm, and fission products of 134Cs and 154Eu were used for evaluating the accuracy of calculation made by CASMO-MICBURN and ORIGEN-2 codes. The effect of Gd on the neutron spectrum was taken into account in the CASMO-MICBURN calculation. The amounts of 235U, 239Pu and 241Pu calculated by CASMO-MICBURN agreed well with the observed values within about 3%. On the other hand, the amounts obtained from ORIGEN-2 calculation showed lower values than those observed, especially by —12% in average in 235U for Gd203U02 fuel. The main cause of this large difference may be attributed to the effect of Gd on the neutron spectrum. The amounts of the other actinides by both calculation codes revealed no significant difference in nearly 10% except for 242mAm, in which a large fluctuation among the samples was observed. About 10% difference between the measured values and the calculated values was also observed for 134Cs, but the calculated values for 154Eu showed a significant difference from measured values. 相似文献
13.
The previous work by our group showed experimental evidence that supports the idea that a diffusion barrier is formed around Gd2O3 agglomerates due to the formation of gadolinium-rich (U,Gd)O2 phases with low diffusivity. This would be the reason for the bad sintering behavior of the UO2-Gd2O3 fuel. The objective of this investigation was to confirm that hypothesis by direct experimental evidence. Analysis of the results showed that the diffusion barrier hypothesis is not applicable. 相似文献
14.
J.L. Gräfe F.E. McNeill S.H. Byun D.R. Chettle M.D. Noseworthy 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2010,268(15):2451-2457
Gadolinium (Gd)-based contrast agents are a valuable diagnostic aid for magnetic resonance imaging (MRI). The amount of free Gd deposited in tissues following contrast enhanced MRI is of toxicological concern. The McMaster University in vivo prompt gamma neutron activation analysis facility has been adapted for the detection of Gd in the kidney, liver, and the leg muscle. A simple model of the HPGe detector used for detection of the prompt γ-rays following Gd neutron capture has been created using Monte Carlo simulation. A separate simulation describing the neutron collimation and shielding apparatus has been modified to determine the neutron capture rate in the Gd phantoms. The MCNP simulation results have been confirmed by experimental measurement. The deviations between MCNP and the experiment were between 1% and 18%, with an average deviation of 3.8 ± 6.7%. The validated MCNP model is to be used to improve the Gd in vivo measurement sensitivity by determining the best neutron moderator/reflector arrangement. 相似文献
15.
《Journal of Nuclear Science and Technology》2013,50(11):1086-1092
Displacement chromatographies of Gd adsorption band in cation exchange resin were performed to observe the isotope effects in the Gd ion exchange processes involving complex forming reagents. The heavy isotope of 160Gd was found to be enriched at the front boundary of Gd adsorption band and the lighter isotopes of 1MGd, 156Gd and 157Gd were enriched at the rear boundary in both cases of 20.1m elution with EDTA and 14 m elution with malic acid, as predicted in the theoretical relations. Observed separation coefficients are 4.9×10?5, 4.0×10?5 and 2.5×10?5for isotopie pairs of 156 160Gd, 158Gd and 160Gd, respectively, in the case of EDTA elution. In the case of malic acid elution, smaller separation coefficients were observed as 1.8×10?5, 1.6 5O?5 and 0.92×10?5 for isotopie pairs of 156 160Gd, 157Gd and158 160 respectively. 相似文献
16.
This work presents the electrochemical study of GdCl3 in the molten LiCl-KCl eutectic in the temperature range 723-823 K. Transient electrochemical techniques such as cyclic voltammetry and chronopotentiometry, on an inert metallic tungsten working electrode, have been used in order to investigate the reduction mechanism and transport parameters. This study shows that Gd3+ ions are reduced to Gd metal by a single step mechanism with exchange of three electrons. Diffusion coefficient of GdCl3 ions was determined at various temperatures, at 723 K the value is D = 0.88 10−5 cm2 s−1. Apparent standard reduction potential of the redox couple Gd3+/Gd has been determined by the open-circuit chronopotentiometry technique at several temperatures. Also the Gibbs free energy of GdCl3 formation was determined and compared with thermodynamic data for pure compounds in the supercooled state in order to estimate the activity coefficient of Gd3+ in the molten LiCl-KCl eutectic. 相似文献
17.
A 155Eu/154SmPd3 (about 231 MBq) source for use with 155Gd Mössbauer spectroscopy was developed by a novel method. In the novel method, the isotopically enriched 154SmPd3 compound was prepared by the conventional solid state reaction of 154Sm(HCOO)3 and PdHx in a hydrogen atmosphere at 1273 K for 18 h, which is simpler than the previously reported method. In order to increase the reaction areas, palladium fine particles used to synthesize the PdHx hydride were prepared by a chemical solution process. Performance of the newly developed source was evaluated by observing the 155Gd Mössbauer spectra of known compounds, GdPd3 and cubic Gd2O3 at 12 K. The obtained results indicated that the developed source is fine enough to investigate the structural characteristic of various materials containing gadolinium. 相似文献
18.
M.V KrishnaiahG Seenivasan P Srirama MurtiC.K Mathews 《Journal of Nuclear Materials》2002,306(1):10-14
The knowledge of thermophysical properties of the rare earth uranium ternary oxides of the type RE6UO12 (RE=La, Gd and Dy) is essential to understand the fuel performance during reactor operation and for modeling fuel behavior. Literature on the high temperature properties of this compound is not available and there is no report at all on the thermal conductivity of these compounds. Hence a study of thermal conductivity of this compound has been taken up. The compounds were synthesized by a solution combustion method using metal nitrates and urea. Thermal diffusivity of these compounds was measured by the laser flash method in the temperature range 673-1373 K. The specific heat data was computed using Neumann-Kopp’s law. Thermal conductivity was calculated using the measured thermal diffusivity value, density and specific heat data for different temperatures. The temperature dependence of thermal conductivity and the implication of structural aspects of these compounds on the data are discussed here. 相似文献
19.
20.
Glass-ceramic waste forms such as zirconolite (nominally CaZrTi2O7) based ones can be envisaged as good candidates for minor actinides or Pu immobilization. Such materials, in which the actinides (or lanthanides used as actinide surrogates) would be preferentially incorporated into zirconolite crystals homogeneously dispersed in a durable glassy matrix, can be prepared by controlled crystallization (nucleation + crystal growth) of parent glasses belonging to the SiO2-Al2O3-CaO-ZrO2-TiO2 system. In this work we present the effects of the nature of the minor actinide surrogate (Ce, Nd, Eu, Gd, Yb, Th) on the structure, the microstructure and the composition of the zirconolite crystals formed in the bulk of the glass-ceramics. The amount of lanthanides and thorium incorporated into zirconolite crystals is discussed in relation with the capacity of the glass to accommodate these elements and of the crystals to incorporate them in the calcium and zirconium sites of their structure. 相似文献