Information Last Revised:
TTP Reference Number: AL911201-G3
1. Technical Name of Technology: Prompt Fission Neutron (PFN) Logging System
2. Common Name of Technology: PFN Logging
3. PI and Telephone No: D. C. George, (303) 248-6699
4. Affiliation: Chem-Nuclear Geotech, Inc.
5. Technology Category: Characterization and monitoring technologies.
6. Developers: Buried Waste Integrated Demonstration (BWID).
7. Application
7.1. Where (in-situ/ex-situ): In-situ.
7.2. Media: Soil and rock surrounding borehole.
7.3. Targeted Contaminants: Fissile materials, principally uranium-235 and plutonium-239.
8. Scope of project (feasibility study, treatability, bench, pilot, field):
Technology development, fabrication, feasibility.
9. Integrated Demonstration (ID) Need/Requirements:
This technology addresses the need for better methods to characterize subsurface geohydrologic features, for in-situ methods of characterizing contaminants, and for understanding subsurface contaminant behavior.
10. Objective
10.1. Objective of technology:
The objective of this subtask is to demonstrate, test, and evaluate the ability of existing borehole logging technology to characterize subsurface contamination and its environment. A state-of-the-art, digital, slim-hole system and existing neutron/gamma-ray transport codes are being used to develop field methods, calibration procedures, environmental corrections, and interpretation techniques that are relevant to characterization of contaminated sites at DOE facilities. Emphasis is being placed on the evaluation of an existing high energy (14 million electron volt) prompt fission neutron (PFN) logging probe with a neutron detector to quantify fissile (e.g., U-235, Pu-239) contaminants.
10.2. Baseline (baseline technology to which it is compared):
Sample / Offsite Analysis (Offsite Analysis)
11. Process Description:
The logging system is self-contained and operates as a stand-alone. During field operations the probe is lowered into a borehole and data are collected. These data are stored digitally, processed rudimentarily, and displayed to permit quality assurance and initial interpretation. At a later time the data are processed in detail and interpreted.
To generate PFN data, the instrument generates a short burst of neutrons using a linear accelerator in a sealed tube within the probe. The neutrons penetrate the soil and rock surrounding the borehole but are slowed down and eventually captured by other atoms. The atoms that capture neutrons, U-235 and Pu-239 (and other elements with comparable fission cross sections), spontaneously fission producing additional neutrons. These additional neutrons are counted by a detector which is shielded so that it detects only the energetic neutrons from fission. The observed count-rate, which varies as a function of time after each neutron burst, is related to the partial density of fissionable elements in the soil.
11.1. Input:
The PFN tool bombards the region (a 2 foot radius) immediately around the borehole with a burst of 14 MeV neutrons at a repetition rate of 100 per second. The neutrons decelerate and are absorbed by atoms within the formation. If fissionable material is present an absorbed neutron can cause the atom to fission, generating additional epithermal neutrons. These additional neutrons are detected to indicate the presence of fissionable elements.
11.2. Output:
The PFN tool contains an epithermal neutron detector to count the frequency of neutrons returned to the borehole after the neutron burst. Epithermal neutrons detected after 200 microseconds are due to fission reactions.
12. Summary of Technology Advantages (relative to the baseline: faster, better, cheaper, safer):
An advantage of PFN technology is that it provides a near-continuous profile of contaminants as a function of position along the borehole; data points spaced at 0.1 ft or 0.2 ft are common. Another advantage is that it analyzes some 10³ times larger volume of material than an individual sample. Furthermore, PFN logging provides the opportunity to repeat measurements in the same borehole, year after year, for monitoring purposes.
PFN logging can produce in-situ assay data in a fraction of the time that it takes to submit all of the samples from a borehole to an analytical laboratory, and obtain results. With the PFN system, the time to log the hole is on the order of a few hours, and results are available instantly.
The cost of drilling a borehole in contaminated soil has been reported by Hanford personnel to be $1000 to $2000 per foot, or approximately $150,000 for a 100 foot borehole. A representative sampling scenario for such a borehole might be to extract and analyze 20 samples taken at 5 foot intervals, at a cost of some $5000 per sample ($100,000 for a 100 foot borehole). If the borehole is cased and the inside of the casing is uncontaminated, it can be logged for about $1000 as part of a multiple hole program. If PFN logging is successful, it should be possible to reduce the sampling and analysis by more the 25%, as a conservative estimate, for a net savings of $24,000 for this borehole. Extending this to the hundreds of boreholes anticipated in the DOE environmental remediation program shows that the claim for potential savings of millions of dollars under this scenario is not an exaggeration.
13. Limitations of Technology (relative to the baseline: faster, better, cheaper, safer):
Borehole sampling has the advantage of providing a sample which can be analyzed under controlled conditions. In the laboratory, the sample can be assayed as accurately as possible within the state-of-the-art, and an analytic method can be chosen which is optimum for the task. To save costs, assays may be done only for samples collected at periodic points along the axis of the borehole rather than for all samples collected.
The PFN system can not provide assays for waste concentrations as low as is possible in the laboratory. The lower limit of detection for the system is believed to be on the order of 1 nCi/g Pu-239 while some regulatory limits are in the range of picocuries per gram. Also, borehole sampling represents a safer alternative to PFN as no radiation exposure hazard exists from handling sources in the field.
14. Major Technical Challenges:
Major challenges include: (1) Procurement of a suitable neutron generator and upgrading the existing logging system with digital acquisition capability. (2) Develop numerical models to characterize anticipated waste site conditions. (3) Perform modeling experiments and calibrations to establish the sensitivity of the system to contaminants, borehole effects and the host medium. (4) Locate a suitable test site, conduct field demonstrations and interpret.
15. Technical Effectiveness:
15.1. Performance
15.1.1. Remaining Contamination: (contamination mobility reduction, volume reduction, toxicity reduction)
Summary (20 words or less): Not applicable
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15.1.2. Process Waste
15.1.2.1. Status of waste (mobility, volume, hazard, recyclability)
Summary (20 words or less): Not applicable
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15.1.2.2. Treatment (needed, available)
Summary (20 words or less): Not applicable
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15.1.2.3. Decontamination / Decommissioning
Summary (20 words or less): Not applicable
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15.1.2.4. Disposal (needed, available)
Summary (20 words or less): Not applicable
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15.1.3. Practicality
15.1.3.1. Foreclose Future Options
Summary (20 words or less): No effect on future options.
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15.1.3.2. Reliability
Summary (20 words or less): The PFN probe is expected to perform routine data collection incurring <20% production down-time.
Further Description (unlimited length): The technology will be developed so that repeated logging attempts over the same interval produces identical results. Any doubt about reliability can be immediately resolved by examining the instrument precision in this fashion.
15.1.3.3. Failure Control
Summary (20 words or less): No immediate response due to system failure.
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15.1.3.4. Ease of Use
Summary (20 words or less): This system is designed for use by a knowledgeable technician fully trained in logging procedures.
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15.1.3.5. Infrastructure
Summary (20 words or less): Cased boreholes with a minimum internal diameter of 5 inches must be available to provide access to the subsurface.
Further Description (unlimited length): Also, the system will be utilized with a truck mounted winch which will require borehole access via a road.
15.1.3.6. Versatility
Summary (20 words or less): The technique can be used to detect and quantify any fissile materials.
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15.1.3.7. System Compatibility
Summary (20 words or less): Electronic output is compatible with most existing systems.
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15.1.3.8. Off-the-Shelf (procurement ease)
Summary (20 words or less): This instrument will contain already fabricated components, and could be readily assembled and provided by commercial sources.
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15.1.3.9. Maintainability
Summary (20 words or less): The system can be maintained similarly to electronic field instruments.
Further Description (unlimited length): Some care is required to reduce physical strain on the sonde and cable which can be troublesome..
15.1.3.10. Safety Measures
Summary (20 words or less): Of concern is the potential for human exposure to neutron bursts.
Further Description (unlimited length): Appropriate field procedures eliminate this risk because no radiation is generated until power is applied to the probe.
15.1.4. "Works" (functions as intended):
Summary (20 words or less): Field demonstrations scheduled for Hanford, WA in 1993 will prove or disprove the applicability of this technique.
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15.2. Cost
15.2.1. Start-Up Cost
Summary (20 words or less): The projected cost of development calls for an expenditure of $645K to produce a prototype system.
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15.2.2. Operations and Maintenance Cost
Summary (20 words or less): A very crude estimate to operate PFN on a prototype basis 25 hours/week may require 10 hours of maintenance.
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15.2.3. Life-cycle cost
Summary (20 words or less): A cost estimate is not possible. No commercial version of this system is presently available.
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15.3. Time
15.3.1. Years Until Available
Summary (20 words or less): A prototype system will be developed over a three year period (FY 1992 - FY 1994) and should be available by 9/30/94.
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15.3.2. Speed/Rate
Summary (20 words or less): Approximately three hours are necessary to log and analyze a typical 100 foot borehole.
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15.3.3. Years to Finish
Summary (20 words or less): A prototype system will be developed over a three year period (FY 1992 - FY 1994) and should be available by 9/30/94.
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16. Environmental Safety and Health
16.1. Worker Safety
16.1.1. Exposure to Hazardous Materials/Hazards
Summary (20 words or less): If improperly handled or operated, there is some potential for operator exposure to neutron bombardment from the generator.
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16.1.2. Physical Requirements
Summary (20 words or less): The technology will require handling of 50 pound tools, a winch, and a 11 foot probe required for the logging operation.
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16.1.3. Number of People Required
Summary (20 words or less): Two people are required to safely handle the system.
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16.2. Public Health and Safety
16.2.1. Accidents
Summary (20 words or less): No public health issues are apparent if technology is used at toxic waste sites only.
Further Description (unlimited length): Use of the technology in and around aquifers would be of concern if the tool with the neutron source were lost in the borehole and abandoned.
16.2.2. Routine Releases
Summary (20 words or less): Not applicable
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16.2.3. Transportation
Summary (20 words or less): Not applicable
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16.3. Environmental Impacts
16.3.1. Ecological Impacts
Summary (20 words or less): No ecological impacts are anticipated if the technology used in and around toxic wastes.
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16.3.2. Aesthetics
Summary (20 words or less): Not applicable
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16.3.3. Natural Resources
Summary (20 words or less): Not applicable
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16.3.4. Energy Demands
Summary (20 words or less): Energy usage is minimal (< 100 watts)
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17. Socio-Political Interests
17.1. Public Perception
17.1.1. Proponent Reputation
Summary (20 words or less): There should be no public concern about the use of this technology in and around toxic waste sites.
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17.1.2. Familiarity / Understandability
Summary (20 words or less): Interested non-technical parties and individuals are unlikely to be familiar with this technology.
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17.2. Tribal Rights / Future Land Use
17.2.1. Capacity for Unrestricted Use (terrestrial, aquatic)
Summary (20 words or less): No restrictions should be placed on applications of this non-intrusive technology.
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17.3. Socio-Economic Interests
17.3.1. Economic Impacts
Summary (20 words or less): Not applicable
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17.3.2. Labor Force Demands
Summary (20 words or less): Not applicable
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18. Regulatory Objectives
18.1. Compatibility with Cleanup Milestones
Summary (20 words or less): Not applicable
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18.2. Regulatory Infrastructure / Track Record
Summary (20 words or less): Not applicable
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18.3. Regulatory Compliance
Summary (20 words or less): Not applicable
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19. Industrial Partnerships
19.1. Company Names:
None at this time.
19.2. Rationale:
19.3. Contract Mechanism:
19.4. Other Potential Companies:
19.5. International:
20. Intellectual Property
20.1. Patent Ownership:
Department of Energy
20.2. Other Owners:
20.3. Patent Number:
21. Cost Sharing:
Related work is being performed under the Mixed Waste Landfill Integrated Demonstration and the Characterization, Monitoring and Sensors Technology Integrated Program. The respective programs involve the development of Neutron Activation Logging using a multi-element probe, and a new generator Pulsed-Neutron Induced Gamma-Ray Multi-Spectral (MS) Logging System for in-situ mapping of contaminants. These three programs benefit by sharing generator procurement and modeling costs. Although there is a synergistic relationship between the PFN, ME and MS programs, no formal expense sharing routine is in place.
22. Background on this technology (Where did the idea come from? Who else is doing similar work? What have the results been to date? What is the most significant competitor to this technology?):
During the National Uranium Resource Evaluation (NURE) program, GJPO played a leading role in developing state-of-the-art borehole logging technology used in assaying for uranium in small-diameter (i.e., <4-inch) boreholes. At a cost of more than $3M, two types of probes were developed under an agreement with Sandia National Laboratory-Albuquerque: the PFN probe and the ME probe. Both probes use high-energy (14 million electron volt) neutron generators.
The PFN probe detects epithermal neutrons, the population of which is influenced by the presence of fissile elements (e.g., uranium and plutonium) (Humphreys et al. 1981). The probe also detects thermal neutron density by detecting gamma rays produced as a result of neutron captures. Recent work reported (Stromswold et al. 1989) demonstrates that these probes also can be used as porosity devices or moisture gauges. An advantage of using a PFN probe for porosity or moisture measurements is that no isotopic neutron source is employed.
23. Reference Documents:
Humphreys, D. R., R. W. Barnard, H. M. Bivens, D. H. Jensen, W. A. Stepheson, and J. H. Weinlein, 1981. "Uranium Logging by the Prompt Fission Neutron Technique," IEEE Trans. Nucl. Sci., v. NS-28, n. 2, pp. 1691-1695
Stromswold, D. C., W. R. Mills, R. D. Wilson, and J. K. Cook, 1989. "Formation Porosity Measurements Using Epithermal Neutron Lifetime," IEEE Trans. Nucl. Inst., V. NS-36, n. 1, pp. 1210-1214.