14 research outputs found
Recommended from our members
Temperature logging as an aid to understanding groundwater flow in boreholes
Borehole temperatures are affected by a range of physical phenomena, including drilling and engineering procedures, thermal resistivity of the rock, surface climatic changes, local heat sources and sinks, free convection of the borehole fluid, and water flows inside the borehole. As a result, temperature logs provide unique information not available from other logs. On the other hand, because the temperature log is sensitive to a variety of phenomena, one or more of these may obscure the effect being studied. In the case where groundwater is entering the borehole at one depth and exiting at another depth (or at the surface) the temperature disturbance resulting from this flow is likely to be a prominent feature of the temperature profile of the borehole. Because of this, water flows in boreholes are often a source of noise in temperature logs, obscuring the features of interest. Recently, however, unusual groundwater behavior was noted in several boreholes at the Nevada Test Site (NTS), and temperature logs were run as part of a program to study this phenomenon. In this case the groundwater flow has been the feature of interest in the logs, and the logs have been useful as an aid in understanding the water flow in those boreholes
Recommended from our members
Spectral gamma-ray log data analysis for NTS borehole ER-20-6 {number_sign}2
Borehole ER20-6 {number_sign}2 was drilled in Area 20 (Pahute Mesa) at the Nevada Test Site near the site of the Bullion underground nuclear test. Radionuclides include Co-60, Ru-106, Sb-125, Cs-134, and Cs-137. Bullion was conducted in June, 1990, at a depth of 2,211 ft. This report presents their interpretation of the Western Atlas spectral gamma-ray data from that borehole along with a quality analysis of the contractor`s data and procedures. A brief description of the spectral gamma-ray logging equipment used in the Underground Test Area work, including some of the deficiencies of the equipment and procedures, is given in Appendix A
Recommended from our members
Programs and procedures for assessing quality of spectral gamma-ray borehole data for the UGTA
This report describes the procedures and computer programs used to process spectral gamma-ray borehole logging data in the UGTA (UnderGround Test Area) program at the NTS (Nevada Test Site) to assess data quality. These programs and procedures were used to analyze data from five boreholes in the UGTA program. Development of these computer programs and procedures required considerable effort and the primary purpose of this report is to provide continuity with future activities related to spectral gamma-ray borehole logging in the UGTA program. This is especially important because of the long time interval between cessation of logging in April, 1996 and the next round of activity, which has not yet occurred. This report should also be useful if any quality control issues arise regarding past or forthcoming spectral gamma-ray log analyses. In the characterization work underway at the Nevada Test Site Underground Test Area, the logging contractor, Western Atlas, agreed to identify five artificial nuclides based on their gamma-ray signatures. Those nuclides are {sup 60}Co, {sup 106}Ru, {sup 125}Sb, {sup 134}Cs, and {sup 137}Cs. In the case of {sup 106}Ru, which is not a gamma emitter, any detected gamma rays come from the daughter nuclide {sup 106}Rh which has a half-life of 30 s. With such a short half-life, {sup 106}Rh can be considered to be in equilibrium with {sup 106}Ru under most conditions so the result is the same as if the gamma rays were emitted by the {sup 106}Ru. The Western Atlas spectral gamma-ray curve plots from a given borehole present detailed qualitative information on the apparent distribution of natural and artificial nuclides with depth in the borehole. The computer programs and procedures described in this report were used to provide a quality analysis of the contractor`s processed data and to work with the contractor to validate and/or refine their existing automatic processing. This was done using a procedure that was developed and tested successfully in earlier work at the NTS; the revised and updated procedure is documented in this report
Recommended from our members
A new computationally-efficient computer program for simulating spectral gamma-ray logs
Several techniques to improve the accuracy of radionuclide concentration estimates as a function of depth from gamma-ray logs have appeared in the literature. Much of that work was driven by interest in uranium as an economic mineral. More recently, the problem of mapping and monitoring artificial gamma-emitting contaminants in the ground has rekindled interest in improving the accuracy of radioelement concentration estimates from gamma-ray logs. We are looking at new approaches to accomplishing such improvements. The first step in this effort has been to develop a new computational model of a spectral gamma-ray logging sonde in a borehole environment. The model supports attenuation in any combination of materials arranged in 2-D cylindrical geometry, including any combination of attenuating materials in the borehole, formation, and logging sonde. The model can also handle any distribution of sources in the formation. The model considers unscattered radiation only, as represented by the background-corrected area under a given spectral photopeak as a function of depth. Benchmark calculations using the standard Monte Carlo model MCNP show excellent agreement with total gamma flux estimates with a computation time of about 0.01% of the time required for the MCNP calculations. This model lacks the flexibility of MCNP, although for this application a great deal can be accomplished without that flexibility
Recommended from our members
Spectral gamma-ray log data analysis for NTS borehole ER-20-6 {number_sign}1
In the characterization work underway at the Nevada Test Site Underground Test Area, the logging contractor, Western Atlas, has been asked to identify five artificial nuclides based on their gamma-ray signatures. Those nuclides are {sup 60}Co (cobalt-60), {sup 106}Ru (ruthenium-106), {sup 125}Sb (antimony-125), {sup 134}Cs (cesium-134) and {sup 137}Cs (cesium-137). The Western Atlas spectral gamma-ray tool uses a 2 in. by 12 in. CsI(Na) (sodium-doped cesium iodide) scintillation detector. Cesium iodide has lower energy resolution than the better known sodium iodide scintillation material but is more rugged and is also more efficient, giving higher count rates especially at higher energies and potentially better counting statistics. Detected gamma rays are divided into 256 energy bins using a pulse-height analyzer in the tool, and the data are transmitted up the logging cable in digital form. Western Atlas personnel perform an energy calibration before and after each logging run using a calibration gamma-ray source. Atlas also performs a running adjustment of the spectral energy scale during the office post-processing based on the positions of known peaks in the naturally occurring spectral components, this is important and will be discussed
Recommended from our members
Identification of artificial gamma-emitting nuclides using a scintillator-based gamma-ray spectral logging system
The standard spectral gamma ray logging system used at the Nevada Test Site (NTS) contains a large sodium iodide detector which provides high efficiency but low energy resolution. To enhance the capabilities of this system for identifying artificial gamma-emitting nuclides, I developed and implemented a simple procedure for extracting artificial components from low-resolution gamma-ray spectra. This procedures uses three bias spectra, developed by a consultant using numerical modeling, representing the spectral response of the downhole instrument to naturally occurring potassium, uranium and thorium family gamma rays in a large-diameter air-filled borehole. To extract the artificial spectral components, the three basis spectra are first scaled to the recorded field spectrum using the usual spectral windows for K, U and Th; these windows bracket the photopeaks at 1.46, 1.76 and 2.61 MeV. Since most of the contribution from artificial nuclides will fall below 1.26 MeV (the lower limit of the potassium window) this scaling process should be insensitive to the presence of artificial nuclides. The scaled basis spectra are then subtracted from the field data, leaving a residual spectrum consisting of noise plus the contribution of any artificial gamma-emitting nuclides. This process is repeated for each spectrum in the log, or the spectra can be accumulated over any desired depth range for better statistics. Rather than inspect each spectrum visually, a parameter can be computed which indicates the presence of artificial nuclides; this parameter can be plotted along with the usual K, U and Th concentration estimates as a function of depth. These techniques have been used successfully on field data and provide us with an inexpensive screening tool to detect artificial nuclides along boreholes. 11 refs., 6 figs
Recommended from our members
Alpha contamination assessment for D&D activities: Technology overview
Instruments based on the principle of Long-Range Alpha Detection (LRAD) detect the ions created in ambient air by Ionizing radiation, particularly alpha radiation, interacting with air molecules. Using either an electrostatic field or forced convection, these ions can be transported to a detection grid where the ions produce a small current that is measured with a sensitive electrometer. LRAD-based instruments can give separate, simultaneous measurements of alpha-emitting solids and inert radioactive gases such as radon. LRAD-based instruments assess surface contamination on an entire object or large surface area in a single, rapid measurement, including relatively inaccessible areas such as interior surfaces of pipes and process equipment. The LRAD concept is well proven and has been developed into a range of different radiation detection devices. This paper presents an overview of the technology, while several associated papers explore specific applications in greater detail
Recommended from our members
Alpha contamination assessment for D&D activities: Monitoring concrete surfaces
The process of decontaminating and decomissioning former nuclear facilities sometimes requires that large areas of concrete and other materials be scanned to verify they are not contaminated. A specially developed concrete surface monitor (CSM) can greatly expedite that process. The CSM is basically an aluminum box, open on the bottom, that uses an electrostatic field to transport ions created by alpha particles interacting with ambient air to a collection grid or plate. A sensitive electrometer measures the resulting current, which is essentially proportional to surface alpha activity. The initial prototype CSM surveys a surface area of some 300 cm{sup 2} at one time, while a second-generation prototype surveys 2500 cm{sup 2} and is designed to compensate automatically for radon, which can cause substantial errors in estimating surface contamination in some cases. These monitors have been successfully demonstrated on a number of concrete surfaces in situ as well as on concrete pieces cut from former facilities
Recommended from our members
Alpha contamination assessment for D&D activities: Monitoring pipe interiors
We have developed a prototype instrument capable of assessing alpha-emitting contamination on interior surfaces of ducts, pipes, tanks, and other enclosed volumes without inserting a probe. Air is drawn through the potentially contaminated volume and then through a detection grid, where ions created in the air by alpha particles are collected and the resulting charge measured with a sensitive electrometer. A filter at the intake end of the contaminated volume excludes externally created ions, so only ions generated inside the volume are detected. We have studied the response of this prototype in initial experiments using calibrated alpha sources with various pipe diameters and configurations, air flows, and source locations in the pipes. The results of these experiments indicate that this method can be an effective approach to assessing internal contamination
Recommended from our members
Simulations of a spectral gamma-ray logging tool response to a surface source distribution on the borehole wall
We have developed Monte Carlo and discrete ordinates simulation models for the large-detector spectral gamma-ray (SGR) logging tool in use at the Nevada Test Site. Application of the simulation models produced spectra for source layers on the borehole wall, either from potassium-bearing mudcakes or from plate-out of radon daughter products. Simulations show that the shape and magnitude of gamma-ray spectra from sources distributed on the borehole wall depend on radial position with in the air-filled borehole as well as on hole diameter. No such dependence is observed for sources uniformly distributed in the formation. In addition, sources on the borehole wall produce anisotropic angular fluxes at the higher scattered energies and at the source energy. These differences in borehole effects and in angular flux are important to the process of correcting SGR logs for the presence of potassium mudcakes; they also suggest a technique for distinguishing between spectral contributions from formation sources and sources on the borehole wall. These results imply the existence of a standoff effect not present for spectra measured in air-filled boreholes from formation sources. 5 refs., 11 figs