Uncertainties in container failure time predictions

Stochastic variations in the local chemical environment of a geologic waste repository can cause corresponding variations in container corrosion rates and failure times, and thus in radionuclide release rates. This paper addresses how well the future variations in repository chemistries must be known in order to predict container failure times that are bounded by a finite time period within the repository lifetime. Preliminary results indicate that a 5000 year scatter in predicted container failure times requires that repository chemistries be known to within {plus minus}10% over the repository lifetime. These are small uncertainties compared to current estimates. 9 refs., 3 figs

Stochastic propagation of an array of parallel cracks: Exploratory work on matrix fatigue damage in composite laminates

Transverse cracking of polymeric matrix materials is an important fatigue damage mechanism in continuous-fiber composite laminates. The propagation of an array of these cracks is a stochastic problem usually treated by Monte Carlo methods. However, this exploratory work proposes an alternative approach wherein the Monte Carlo method is replaced by a more closed-form recursion relation based on fractional Brownian motion.'' A fractal scaling equation is also proposed as a substitute for the more empirical Paris equation describing individual crack growth in this approach. Preliminary calculations indicate that the new recursion relation is capable of reproducing the primary features of transverse matrix fatigue cracking behavior. Although not yet fully tested or verified, this cursion relation may eventually be useful for real-time applications such as monitoring damage in aircraft structures

Effects of fill gas composition and pellet eccentricity. [BWR]

Data and an analysis are presented showing that when the operating pellet-cladding gap size of contemporary UO/sub 2/ fuel rods is carefully considered, the gap conductances are closely proportional to the thermal conductivities of the fill gases. Pellet-cladding gap eccentricity is shown to raise the gap conductance appreciably in cases of high thermal gradients across the gap. Ignoring the azimuthal heat flow can lead to an underestimation of the thermal time constant of the rod, resulting in a slower calculated thermal response during power transients. The data for this report were obtained during the startup of the NRC-RSR/BPNL test assembly IFA-431 in the Halden Boiling Water Reactor in Norway

Method for determining the uncertainty of gap conductance deduced from measured fuel centerline temperatures. [BWR]

The paper describes the method which was developed to determine the uncertainties of gap conductances deduced from measured fuel centerline temperatures of NRC-RSR/BPNL fuel rods irradiated in the Halden Boiling Water Reactor. The ..integral..k(t)dt method is used to calculate the fuel surface temperature from the measured fuel centerline temperature and the fuel thermal conductivity. The gap conductance is calculated from the fuel surface temperature, the calculated cladding inside surface temperature, and the measured fuel assembly power. The uncertainties in the input parameters for calculating the gap conductance were established and the uncertainty in the gap conductance was calculated using the method of propagation of uncertainties with a first order Taylor series approximation to the nonlinear functions. An example of the calculational method is given

Ion-Beam-Induced Defects and Defect Interactions in Perovskite-Structure Titanates

Ion-beam irradiation of perovskite structures results in the production and accumulation of defects. Below a critical temperature, irradiation also leads to a crystalline-to-amorphous transformation. The critical temperature for amorphization under 800 keV Kr{sup +} ion irradiation is 425,440 and 550 K for SrTiO{sub 3}, CaTiO{sub 3} and BaTiO{sub 3}, respectively. The results of ion-channeling studies on SrTiO{sub 3} irradiated with 1.0 MeV Au{sup 2+} ions suggest that the crystalline-to-amorphous transformation is dominated by the accumulation and interaction of irradiation-induced defects. In SiTiO{sub 3} irradiated with He{sup +} and 0{sup +} ions at 180 K, isochronal annealing studies indicate that there is significant recovery of defects on both the oxygen and cation sublattices between 200 and 400 K. These results suggest that defect recovery processes may control the kinetics of amorphization. A fit of the direct-impact/defect-stimulated model to the data for SrTiO{sub 3} suggests that the kinetics of amorphization are controlled by both a nearly athermal irradiation-assisted recovery process with an activation energy of 0.1 plus or minus 0.05 eV and a thermal defect recovery process with an activation energy of 0.6 plus or minus 0.1 eV. In SrTi0{sub 3} implanted with 40 keV H{sup +} to 5.0 x 10{sup 16} and 1.0 x 10{sup 17} ions/cm{sup 2}, annealing at 470 K increases the backscattering yield from Sr and Ti and is mostly likely due to the coalescence of H{sub 2} into bubble nuclei. Annealing at 570 K and higher results in the formation of blisters or large cleaved areas

Analysis of fuel relocation for the NRC/PNL Halden assemblies IFA-431, IFA-432, and IFA-513

The effects of the thermally-induced cracking and subsequent relocation of UO/sub 2/ fuel pellets on the thermal and mechanical behavior of light-water reactor fuel rods during irradiation are quantified in this report. Data from the Nuclear Regulatory Commission/Pacific Northwest Laboratory Halden experiments on instrumented fuel assemblies (IFA) IFA-431, IFA-432, and IFA-513 are analyzed. Beginning-of-life in-reactor measurements of fuel center temperatures, linear heat ratings, and cladding axial elongations are used in a new model to solve for the effective thermal conductivity and elastic moduli of the cracked fuel column. The effective thermal conductivity and elastic moduli for the cracked fuel were found to be significantly reduced from the values for solid UO/sub 2/ pellets. The calculated fuel-cladding gap remained relatively constant (closed) with respect to power level, indicating that the fuel fragments do not retreat from the cladding when the power/temperature is reduced. Recommendations are made pertaining to the work required to further refine the model. 30 refs., 81 figs., 8 tabs

Identification of energy conservation research opportunities: a review and synthesis of the literature

Thirty-eight studies of energy conservation research opportunities are reviewed. The 38 studies chosen for review include many of the major efforts in the identification of energy conservation research and development (R and D) opportunities and provide a representative sample of the types of studies that have been performed. The sample includes studies that focus on specific energy use (e.g., auto transport), as well as studies that focus on specific types of research (e.g., materials science). The sample also includes studies that can be further contrasted in terms of long-term vs. short-term projects, evolutionary vs. revolutionary ideas, generic vs. process-specific activities, and technology base research vs. hardware development. Each of these perspectives contributes toward assuring coverage of the breadth of energy conservation R and D opportunities. In each review the technical or end-use focus is described, the research ideas identified in the study are listed, and a critical summary is given. The reviews also indicate whether the studies present end-use consumption data, estimate potential energy savings, estimate times to commercialization, summarize existing research programs, or describe the identification methodology. In Section 2.0 the various research studies are compared. In Section 3.0 the characteristics of an aggregate list of research ideas are discussed. The characteristics were collected from the research opportunities studies, which are included in Appendix A. Appendix A contains a compilation of energy conservation R and D opportunities arranged by energy end-use applications. Appendix B contains an outline of the format followed in writing the critical reviews of the studies, the individual study reviews, and the extended bibliography of 88 studies that describe energy conservation research opportunities

Spent nuclear fuel as a waste form for geologic disposal: Assessment and recommendations on data and modeling needs

This study assesses the status of knowledge pertinent to evaluating the behavior of spent nuclear fuel as a waste form in geologic disposal systems and provides background information that can be used by the DOE to address the information needs that pertain to compliance with applicable standards and regulations. To achieve this objective, applicable federal regulations were reviewed, expected disposal environments were described, the status of spent-fuel modeling was summarized, and information regarding the characteristics and behavior of spent fuel was compiled. This compiled information was then evaluated from a performance modeling perspective to identify further information needs. A number of recommendations were made concerning information still needed to enhance understanding of spent-fuel behavior as a waste form in geologic repositories. 335 refs., 22 figs., 44 tabs

Episodic photic zone euxinia in the northeastern Panthalassic Ocean during the end-Triassic extinction

Severe changes in ocean redox, nutrient cycling, and marine productivity accompanied most Phanerozoic mass extinctions. However, evidence for marine photic zone euxinia (PZE) as a globally important extinction mechanism for the end-Triassic extinction (ETE) is currently lacking. Fossil molecular (biomarker) and nitrogen isotopic records from a sedimentary sequence in western Canada provide the first conclusive evidence of PZE and disrupted biogeochemistry in neritic waters of the Panthalassic Ocean during the end Triassic. Increasing water-column stratification and deoxygenation across the ETE led to PZE in the Early Jurassic, paralleled by a perturbed nitrogen cycle and ecological turnovers among noncalcifying groups, including eukaryotic algae and prokaryotic plankton. If such conditions developed widely in the Panthalassic Ocean, PZE might have been a potent mechanism for the ETE