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Evaluation of kriging techniques for high level radioactive waste repository site characterization

Description: Kriging is a statistical method for estimating functions that describe spatially distributed phenomena such as groundwater elevation and depth to basalt. It produces a contour model of the geologic formation of a potential site with an associated measure of uncertainty, and it can be used to optimize the selection of additional sampling locations. Kriging was applied to water potential data and top-of-basalt elevations from the Hanford site; the computer code BLUEPACK was used to perform the computations. The water potential contours were in close agreement with a hand-drawn contour map which is used as a standard. It is concluded that kriging can be a useful tool for geologic waste repository site characterization. (DLC)
Date: January 1, 1979
Creator: Doctor, P.G.
Partner: UNT Libraries Government Documents Department

Geostatistical Modeling of Pore Velocity

Description: A significant part of evaluating a geologic formation as a nuclear waste repository involves the modeling of contaminant transport in the surrounding media in the event the repository is breached. The commonly used contaminant transport models are deterministic. However, the spatial variability of hydrologic field parameters introduces uncertainties into contaminant transport predictions. This paper discusses the application of geostatistical techniques to the modeling of spatially varying hydrologic field parameters required as input to contaminant transport analyses. Kriging estimation techniques were applied to Hanford Reservation field data to calculate hydraulic conductivity and the ground-water potential gradients. These quantities were statistically combined to estimate the groundwater pore velocity and to characterize the pore velocity estimation error. Combining geostatistical modeling techniques with product error propagation techniques results in an effective stochastic characterization of groundwater pore velocity, a hydrologic parameter required for contaminant transport analyses.
Date: June 1, 1981
Creator: Devary, J.L. & Doctor, P.G.
Partner: UNT Libraries Government Documents Department

Pattern recognition methods for acoustic emission analysis

Description: Models have been developed that relate the rate of acoustic emissions to structural integrity. The implementation of these techniques in the field has been hindered by the noisy environment in which the data must be taken. Acoustic emissions from noncritical sources are recorded in addition to those produced by critical sources, such as flaws. A technique is discussed for prescreening acoustic events and filtering out those that are produced by noncritical sources. The methodology that was investigated is pattern recognition. Three different pattern recognition techniques were applied to a data set that consisted of acoustic emissions caused by crack growth and acoustic signals caused by extraneous noise sources. Examination of the acoustic emission data presented has uncovered several features of the data that can provide a reasonable filter. Two of the most valuable features are the frequency of maximum response and the autocorrelation coefficient at Lag 13. When these two features and several others were combined with a least squares decision algorithm, 90% of the acoustic emissions in the data set were correctly classified. It appears possible to design filters that eliminate extraneous noise sources from flaw-growth acoustic emissions using pattern recognition techniques.
Date: July 1, 1979
Creator: Doctor, P.G.; Harrington, T.P. & Hutton, P.H.
Partner: UNT Libraries Government Documents Department

Steam Generator Group Project. Progress report on data acquisition/statistical analysis

Description: A major task of the Steam Generator Group Project (SGGP) is to establish the reliability of the eddy current inservice inspections of PWR steam generator tubing, by comparing the eddy current data to the actual physical condition of the tubes via destructive analyses. This report describes the plans for the computer systems needed to acquire, store and analyze the diverse data to be collected during the project. The real-time acquisition of the baseline eddy current inspection data will be handled using a specially designed data acquisition computer system based on a Digital Equipment Corporation (DEC) PDP-11/44. The data will be archived in digital form for use after the project is completed. Data base management and statistical analyses will be done on a DEC VAX-11/780. Color graphics will be heavily used to summarize the data and the results of the analyses. The report describes the data that will be taken during the project and the statistical methods that will be used to analyze the data. 7 figures, 2 tables.
Date: January 1, 1984
Creator: Doctor, P.G.; Buchanan, J.A.; McIntyre, J.M.; Hof, P.J. & Ercanbrack, S.S.
Partner: UNT Libraries Government Documents Department

Some Aspects of Cost/ Benefit Analysis for In-Service Inspection of PWR Steam Generators

Description: This report discusses a number of aspects of cost/benefit (C/B) analysis for in-service inspection (lSI} of pressurized water reactor (PWR) steam generators (SGs) and identifies several problem areas that must be addressed prior to a full C/B analysis capability. Following a brief review of the impact of SG problems on the productivity of PWR units and of the scope and variability of SG problems among U.S. PWRs, various occupational implications of SG lSI are considered, namely manpower, time, and rad exposure. The opportunities provided by refueling outages in respect to lSI frequency and work time windows are reviewed. Indices for characterizing the nondestructive testing {NDT) information, rad exposure, $ impact, and manpower and time attributes of single ISIs and a series of ISIs over an arbitrary evaluation period are presented and calculated for a number of lSI cases using SG parameters for three typical PWR units. A comparison of the $ impact of unscheduled outages attributable to SG problems with the $ cost of ambitious lSI strategies indicates that the $ cost is virtually negligible for well-planned ISis. Considering the ALARA constraint on occupational rad exposure, the skilled manpower pool for NDT work appears to be the principal factor limiting lSI scope and frequency. Analysis of the manpower and time requirements for inspection of a 40-unit PWR population indicates, however, that an lSI strategy embodying two campaigns per year and a total population inspection within a 2-year interval is not far beyond current capabilities.
Date: May 1, 1981
Creator: Zima, G. E.; Lyon, G. H.; Doctor, P. G.; Hoenes, G. R.; Petty, S. E. & Weakley, S. A.
Partner: UNT Libraries Government Documents Department

Characterization strategy report for the criticality safety issue

Description: High-level radioactive waste from nuclear fuels processing is stored in underground waste storage tanks located in the tank farms on the Hanford Site. Waste in tank storage contains low concentrations of fissile isotopes, primarily U-235 and Pu-239. The composition and the distribution of the waste components within the storage environment is highly complex and not subject to easy investigation. An important safety concern is the preclusion of a self-sustaining neutron chain reaction, also known as a nuclear criticality. A thorough technical evaluation of processes, phenomena, and conditions is required to make sure that subcriticality will be ensured for both current and future tank operations. Subcriticality limits must be based on considerations of tank processes and take into account all chemical and geometrical phenomena that are occurring in the tanks. The important chemical and physical phenomena are those capable of influencing the mixing of fissile material and neutron absorbers such that the degree of subcriticality could be adversely impacted. This report describes a logical approach to resolving the criticality safety issues in the Hanford waste tanks. The approach uses a structured logic diagram (SLD) to identify the characterization needed to quantify risk. The scope of this section of the report is limited to those branches of logic needed to quantify the risk associated with a criticality event occurring. The process is linked to a conceptual model that depicts key modes of failure which are linked to the SLD. Data that are needed include adequate knowledge of the chemical and geometric form of the materials of interest. This information is used to determine how much energy the waste would release in the various domains of the tank, the toxicity of the region associated with a criticality event, and the probability of the initiating criticality event.
Date: June 1, 1997
Creator: Doherty, A.L.; Doctor, P.G.; Felmy, A.R.; Prichard, A.W. & Serne, R.J.
Partner: UNT Libraries Government Documents Department

An example postclosure risk assessment using the potential Yucca Mountain Site

Description: The risk analysis described in this document was performed for the US Department of Energy`s (DOE) Office of Civilian Radioactive Waste Management (OCRWM) over a 2-year time period ending in June 1988. The objective of Pacific Northwest Laboratory`s (PNL) task was to demonstrate an integrated, though preliminary, modeling approach for estimating the postclosure risk associated with a geologic repository for the disposal of high-level nuclear waste. The modeling study used published characterization data for the proposed candidate site at Yucca Mountain, Nevada, along with existing models and computer codes available at that time. Some of the site data and conceptual models reported in the Site Characterization Plan published in December 1988, however, were not yet available at the time that PNL conducted the modeling studies.
Date: May 1, 1992
Creator: Doctor, P.G.; Eslinger, P.W.; Elwood, D.M.; Engel, D.W.; Freshley, M.D.; Liebetrau, A.M. et al.
Partner: UNT Libraries Government Documents Department