Showing papers by "Gary S. Was published in 1985"

The influence of grain boundary precipitation on the measurement of chromium redistribution and phosphorus segregation in Ni-16Cr-9Fe

Abstract: The redistribution of chromium at the grain boundary and the segregation of phosphorus to the grain boundary in Ni-16Cr-9Fe is measured following thermal treatment at 700 °C for 1 to 100 hours. The addition of carbon to the base alloy results in the formation of Cr7C3 precipitates at the grain boundary and the formation of a chromium depleted zone in the adjacent matrix. Measurement of the Cr concentration is affected by the presence of Cr-rich carbides, and a technique of ratioing the Auger signal of the element of interest to a sum of the signals of elements present in the carbide and the matrix is required to minimize the scatter in the data. The presence of carbides does not affect the kinetics or extent of phosphorus segregation to the grain boundary, and there is no evidence of co-segregation of phosphorus with any major alloying element. The free energy of segregation of phosphorus is determined to be 46.2 KJ/mole at 1100 °C and 40.8 KJ/mole at 700 °C. Results show that the intergranular fracture path is along the carbide-matrix interface as opposed to through the carbides or some distance into the matrix. These results permit the calculation of the coverage of the grain boundary with carbides.

Automatic iterative fitting of Rutherford backscattering spectra from multielement samples

Abstract: A computer code (BASF) has been constructed to perform automatic iterative fitting of Rutherford backscattering spectra using only the experimental spectrum and the parameter set defining the experiment. The code may be used to analyze samples containing anywhere from two to five elements. The code output consists of the total amount of each element present and a composition versus depth profile. The code's performance was verified on both computer generated and experimental backscattering spectra. Samples consisting of nickel substrates onto which layers of pure nickel and pure aluminum have been alternately evaporated in thicknesses of 130 and 100 A, respectively, were used to produce backscattering spectra. These spectra, when analyzed, demonstrated that the code was able to determine the total aluminum content to within 3% and the ratio of aluminum to nickel to within 1% of the thickness monitor readings taken during evaporation. The code has shown the ability to recognize sharp interfaces in well resolved spectra. The code performs equally well on slowly varying concentration profiles which are created during the annealing of layered samples. Limitations on the code and its use include the precise knowledge of the relevant experimental parameters used as input, and complete specification of all elements in the sample. The ultimate limits on the code's accuracy are the resolution of the spectrum and the accuracy of the computed stopping powers. This code provides a significant advantage over other spectrum fitting codes in that the process is fully automated and does not require constant user interaction. Further, it provides the capability of accurately determining concentration profiles in layered samples where the layer thickness is of the order 100 A.

The Electrochemical Behavior of P- and C-Doped Ni-16Cr-9Fe

Abstract: High purity Ni-16Cr-9Fe alloys with controlled additions of P and C were annealed and heat-treated to produce all combinations of chromium carbide precipitation, chromium depletion, and phosphorus segregation at the grain boundary. Each alloy heat treatment was subjected to potentiodynamic polarization and electrochemical potentiokinetic reactivation. Polarization scans showed little difference between alloy heat treatments; the most pronounced was a higher critical current density in P-doped alloys. An electrochemical potentiokinetic reactivation (EPR) test solution and method were developed to discriminate between varying degrees of chromium depletion while eliminating the problem of intragranular pitting. The total charge transferred during a reverse scan is not highly sensitive to the variation in Cr in the depleted zone. Dissolution models that are independent of and proportional to the Cr gradient in the depleted zone indicate that the threshold level of Cr below which grain boundaries are ...

FCODE-BETA|SS: a fuel performance code for stainless steel clad pressurized water reactor fuel

Abstract: The FCODE-BETA/SS code, based on the Electric Power Research Institute’s FCODE-BETA, is constructed to model the thermal-mechanical performance of Type 304 stainless steel clad pressurized water re...

Statistical patterns of fuel failure in stainless steel clad light water reactor fuel rods

Abstract: A set of statistical patterns characterizing the conditions for failure of Type 304 stainless steel clad light water reactor fuel is formulated using a 450-assembly cycle data base from the Connecticut Yankee reactor and an information-theoretic (entropy) criterion of pattern formation. The pattern files, consisting of features formulated from output data obtained from the deterministic fuel performance code FCODE-BETA/SS are partitioned into five failure and six nonfailure patterns. The failure probabilities of the patterns span the 0.17 to 37.47% range, as compared with the data base average of 2.86%. Features that contribute to failure patterns include large swings in the linear power at high burnup, frequent stress cycling at the ridge, and low coolant pH at high linear power. Contributing to nonfailure are low fission gas release, high axial uniformity in linear power, peak burnup, and clad creep strain at the ridge. The feature describing cycling of the linear power agrees qualitatively with previously identified factors contributing to failure of stainless steel clad fuel in the Connecticut Yankee reactor. From an operational standpoint, the fuel failure probability can be reduced by minimizing the number and magnitude of power ramps and maintaining a neutral coolant pH.

Automatic Iterative Fitting of RBS Spectra from Multielement Samples

Abstract: A computer code (BASF) has been constructed to perform automatic iterative fitting of smoothed Rutherford Backscattering Spectra using only the experimental spectrum and the parameter set defining the experiment. The code may be used to analyze anywhere from two to five elements. The code output consists of the total amount of each element present and a composition versus depth profile. The code’s performance was verified experimental backscattering spectra. Samples consisting of nickel substrates onto which layers of nickel and aluminum have been alternately evaporated were used to produce backscattering spectra. These spectra, when analyzed, demonstrated that the code was able to determine the total aluminum content to within 5% and the ratio of aluminum to nickel within 1% of the thickness monitor readings taken during evaporation. The code has also shown the ability to recognize sharp interfaces in well resolved spectra. The ultimate limits on the code’s accuracy are the resolution of the spectrum and the accuracy of the computed stopping powers.

Phase Transformations in Nickel-Aluminum Alloys During Ion Beam Mixing

Abstract: The effect of ion beam mixing of nickel-aluminum alloys with 500 keV krypton ions has been investigated over a range of temperature, composition, ion dose, and post-irradiation thermal treatments. Samples were formed by alternate evaporation of layers of aluminum and nickel. A portion of these samples was subsequently annealed to form intermetallic compounds. Irradiations were performed at both room temperature and 80/sup 0/K using the 2MV ion accelerator at Argonne National Laboratory. Phase transformations were observed during both in situ irradiations in the High Voltage Electron Microscope (HVEM) at Argonne, and also in subsequent analysis of an array of irradiated samples. Electron diffraction indicates the presence of metastable crystalline structures not present in the conventional nickel-aluminum phase diagram. Transformations occur at doses as low as 5 x 10/sup 14/ cm/sup -2/ and continue to develop as the irradiation progresses up to 2 x 10/sup 16/ cm/sup -2/. Layer mixing is followed through Rutherford Backscattering analysis. Samples are also checked with x-rays and Electron Energy Loss Spectroscopy (EELS). A thermodynamic argument is presented to explain the phase transformations in terms of movements on a free energy diagram. This analysis explains the interesting paradox concerning the radiation hardness of the NiAl phasemore » and the amorphous structure of mixed Ni-50% Al layers.« less