Regulatory Guide 3.11
| ML13038A425 | |
| Person / Time | |
|---|---|
| Issue date: | 10/31/1980 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| References | |
| RG-3.011.1, Rev 1 | |
| Download: ML13038A425 (8) | |
Revision 1*
October 1980
U.S. NUCLEAR REGULATORY COMMISSION
REGULATORY GUIDE
OFFICE OF STANDARDS DEVELOPMENT
REGULATORY GUIDE 3.11.1 OPERATIONAL INSPECTION AND SURVEILLANCE OF EMBANKMENT
RETENTION SYSTEMS FOR URANIUM MILL TAILINGS
A. INTRODUCTION
tailings are usually stored behind man-made retaining structures, following the practice of the non-uranium Each licensee who processes or refines uranium ores in a mining industry. Unlike most non-uranium mine tailings, milling operation is required by § 20.1 of 10 CFR Part 20, uranium mill tailings contain concentrations of radioactive
"Standards for Protection Against Radiation," to make materials in excess of the allowable discharge limits (Ref. 1).
every reasonable effort to maintain radiation exposures and Furthermore, the most significant radioactive element in releases of radioactive materials in effluents to unrestricted the tailings is radium-226, which has a half-life of about areas as low as is reasonably achievable, taking into account 1600 years (Ref. 2). Therefore, it is necessary to confine the state of technology and the economics of improvements those tailings to prevent or control their release to the in relation to benefits to the public health and safety. In environment not only during the operating life of the mill addition, 40 CFR Part 190, "Environmental Radiation but also for generations after milling operation has ceased.
Standards for Nuclear Power Operations," requires that the The embankment, foundation, and abutments need to be maximum annual radiation dose to individual members of stable to prevent the uncontrolled release of the retained the public resulting from fuel cycle operations be limited to water or semifluid tailings. Seepage from the tailing pond,
25 millirems to the whole body and to all organs except the which contains dissolved radium and other toxic substances thyroid, which must be limited to 75 millirems. Liquid and (Ref. 2), needs to be controlled under normal and severe solid wastes (tailings) generated in the uranium milling operating conditions to prevent the possibility of unaccept- operation contain radioactive materials in excess of the able contamination of the groundwater or nearby streams.
discharge limits and are generally confined by an embank- Wind and water erosion of the tailings needs to be prevented ment retention system. during and after the milling operation.
Regulatory Guide 3.11, "Design, Construction, and Therefore, the design and construction of these facilities Inspection of Embankment Retention Systems for Uranium require a high degree of professional engineering performance.
Mills," describes a general basis for inspection of an embank- The foundation of the dam should be stable and should be ment retention system. This guide, a supplement to Regula- capable of carrying the weight of the structure. The dam tory Guide 3.11, describes in greater detail a basis accept- should be safe under the application of external forces such able to the N RC staff for developing an appropriate inservice as those resulting from earthquakes. The reservoir area inspection and surveillance program for earth and rock fill should be. water retentive and free of the possibilities of embankments used to retain uranium mill tailings. It results dangerous slides. Dams and associated facilities should be from review and action on a number of specific cases and maintained in good working condition throughout their reflects the latest general approaches to the problem. operating lives. Operation and surveillance through the The NRC staff will review any alternative methods to years should be conducted in such a manner that any determine their acceptability. changes in their structural, hydraulic, and foundation conditions can be detected promptly and corrections made.
B. DISCUSSION
Statistics of water retention dam failures, based on the The milling of uranium ores results in the production of sum of operation years of a regional group of dams (Ref. 3),
large volumes of liquid and solid wastes (tailings). These show a frequency of one failure every 1500 to 1800 dam- years. Statistics of uranium mill tailing retention dam failures show a frequency of one failure every 40 dam-years Lines indicate substantive changes from previous issue. (Ref. 4).
USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission, U.S. Nuclear Regulatory Commission, Washington, D.C. 20555, Regulatory Guides are issued to describe and make available to the Attention: Docketing and Service Branch.
public methods acceptable to the NRC staff of implementing specific parts of the Commission's regulations, to delineate tech- The guides are issued in the following ten broad divisions:
niques used by the staff in evaluating specific problems or postu- lated accidents, or to provide guidance to applicants. Regulatory 1. Power Reactors 6. Products Guides are not substitutes for regulations, and compliance with 2. Research and Test Reactors 7. Transportation them is not required. Methods and solutions different from those set 3. Fuels and Materials Facilities 8. Occupational Health out in the guides will be acceptable If they provide a basis for the 4. Environmental and Siting 9. Antitrust and Financial Review findings requisite to the issuance or continuance of a permit or 5. Materials and Plant Protection 10. General license by the Commission.
Copies of issued guides may be purchased at thecurrent Government Comments and suggestions for improvements in these guides are Printing Office price. A subscription service for future guides in spe- encouraged at all times, and guides will be revised, as appropriate, cific divisions is available through the Government Printing Office.
to accommodate comments and to reflect new information or Information on the subscription service and current GPO prices may experience. This guide was revised as a result of substantive com- be obtained by writing the U.S. Nuclear Regulatory Commission, ments received from the public and additional staff review. Washington, D.C. 20555, Attention: Publications Sales Manager.
Causes of latent danger inherent in such works arise needs to be examined for any conditions that may impose I
from site conditions, hydrologic and hydraulic features, constraints on its operation.
types and qualities of the structures, operation and main- tenance, and influence of the environment (Refs. 3, 5, 6, The operation of the slurry transport pipelines seems to and 7). Of these causes, the majority lie within the boundaries be relatively simple, but the frequent ruptures of the of modern technology and can be avoided. Most failures pipelines (Ref. 10) indicate that close monitoring needs to have resulted from gradually worsening defects (due to be performed during operation. A certain degree of segrega- design, construction, operation, or lack of maintenance) tion occurs, with the coarse sand fraction of the tailings that were either undiscovered or misjudged. Table 1 lists the tending to settle at the bottom portion of the pipe. On reported tailing accidents friom 1959 through 1979. relatively steep downslopes, the coarse sand fraction cascades down and, in the process, abrades the pipe wall.
The design and construction of tailing retention structures When air is entrained in the pipeline, the pulp velocity have, in the past, been based largely on mining experience, increases as a result of the reduced cross-sectional area of with little use of design concepts. These empirical approaches the pulp flow and results in relatively fast wear on the pipe have resulted in various mining dam mishaps and failures wall. Regular pipe-wall-thickness determinations will enable (Refs. 8 and 9). The latest advances in geotechnical engineer- various remedial measures to be adopted to alleviate the ing, together with engineering experience and knowledge situation. To help protect against the consequences of available in the field of water storage dams, can be used in slurry ruptures at critical locations, the flow can be caught the design and construction of tailing retention dams. and safely directed by an adequate trough-like device (e.g.,
However, the retention systems may not always perform as a launder). Safety can be further ensured by detecting expected, construction may be defective, and foundations ruptures immediately so measures can be taken quickly.
may need further treatment after a period of operation. To Currently, it is practice to use alarm-triggering flowrate detect such behavior deviations, regular surveillance is sensors installed at nozzle outlets to detect ruptures, essential. cloggings, or other slurry flow irregularities.
The weakening of a dam or its foundation may become Inspection personnel need to be carefully selected, It is apparent only after many years of safe operation. Painstaking monitoring and analysis of performance data are necessary to ensure detection of adverse conditions. Each structure, important that they be practical, dedicated diagnosticians who examine thoroughly every clue during their scrutiny of the behavior of these facilities. They need to be trained to I
as well as each site, has its own characteristics and its be able to recognize and assess signs of possible distress own susceptibilities to problems, and the surveillance or abnormality and to recommend appropriate mitigating program should be tailored to account for these. Mleasures.
Thorough physical examination is an essential part of
C. REGULATORY POSITION
the surveillance program. The optimal frequency of inspec- tions depends on the size and condition of the facilities, the This guide applies to those systems or portions of character of the foundation, the regional geological setting, systems whose failure could cause releases of radioactive'
and the consequences of failure in jeopardizing human effluents in excess of the limits given in 10 CFR Part 20.
life and inflicting property damage. Inservice inspection and surveillance should be performed at regular intervals to check the condition of the retention Before the start of tailing disposal, it is important that systems and associated facilities and to evaluate their records of piezometer levels (including seasonal fluctuations, structural safety and operational adequacy. A detailed, groundwater quality, ground elevations, and background systematic inspection and surveillance program should radioictivities at the site) be compiled so that comparison consist of, but not necessarily be limited to, the following;
can be made with the effects of the impoundment. Data gathered in accordance with Regulatory Guide 4.14, 1. Engineering Data Compilation
"Radiological Effluent and Environmental Monitoring at Uranium Mills," will provide useful information for deter- Engineering dataI related to the design, construction, mining the integrity of tailings dams. As soon as the tailing and operation of the tailing retention systems should be disposal begins, the inspection and maintenance program collected and, to the extent practicable, included in the for structures and operating equipment needs to be initiated. initial inspection report. These data should include the This program includes regular patrol of the dam and its following items, where available and appropriate:
abutments, observations and estimates of seepage flows, piezometric levels related to pond levels, structural and a. General Project Data foundation movements, sampling of groundwater, and examination of slurry transport and decant pipelines. (1) Regional vicinity map showing the project Attention also needs to be focused on inspection and data location and the upstream and downstream drainage areas.
collection during relatively rapid changes in reservoir 1 water surface elevations. The emergency discharge facility Most engineering data (as presented in accordance with Regula- tory Guide 3.11 and Section 2.5.6 of Regulatory Guide 1.70, "Stand- (for disposing of floodwater runoff in excess of designed ard Format and Content of Safety Analysis Reports for Nuclear pond capacity) may consist of diversion channels, spillways, Power Plants") are readily available in documents filed for a mill license application. A detailed reference or the original documents culverts, or other designs. To ensure proper operation, it kept at the project site should be adequate.
3.11.1-2
(2) As-built drawings and photographs of important a. Daily Inspection project features, including details of decant systems and typical installation of instrumentation (e.g., sectional views (1) Decant systems should be examined for any and material zoning and foundation stratification, final top evidence of clogging of the intake; corrosion, cracking, or and bottom elevation, gradation and properties of materials crushing of decant pipes; and erosion at the discharge point.
placed in installation). The character and quantity of water flowing into the inlet and flowing out of the discharge should be compared for evidence of cracks or open joints.
b. Hydrologic and Hydraulic Data
(2) Effluent from underdrain pipes should be exam-
(1) Drainage area and basin characteristics. ined for evidence of clogging, cracking, and erosion.
(2) Storage for tailings and surcharge capacities for (3) Pond water elevations should be examined and floods and rate of slurry inflow. recorded to correlate them with piezometer levels and to ensure that minimum freeboard is maintained.
(3) Elevation of the maximum design pool and freeboard height. (4) The slurry transport system should be examined for any evidence of obstruction of the pipes or pumps due
(4) Outlet facility characteristics (location, type, to sand clogging or ice accumulation. The pipe couplings dimensions, and elevation). should be examined for leakage of slurry, any flowrate sensor should be tested, and any launder examined to c. Foundation data and geological features, including ensure proper operation.
boring logs, geological maps, profiles, and cross sections.
(5) The retention dam should be visually inspected d. Properties of embankment and foundation materials, for signs of cracking, slumping, movement, or concentration including results of laboratory tests and field tests, and of seepage.
assumed design material properties.
b. Monthly Inspection e. Pertinent construction photographs and records, including construction control tests, dewatering method (1) Slurry transport pipes should be examined using and construction problems, alterations, modifications, and an ultrasonic device at locations where pipes cross streams maintenance repairs. or other natural water courses or where a rupture of the pipe could be expected to affect the stability of the embankment.
f. Contingency plan, including a plan for the regulation of pond water elevation under normal conditions and (2) Diversion channels should be examined for during flood events or other emergency conditions. channel bank erosion, bed aggradation or degradation and siltation, obstruction to flow, undesirable vegetation, or g. Principal design assumptions and analyses, including any unusual or inadequate operational behavior.
hydrologic and hydraulic analyses, stability and stress analyses, and seepage and settlement analyses. c. Quarterly Inspection h. Special license conditions and discussion on how (1) Embankment Settlement. The top of the embank- these conditions have been met. ment and downstream toe areas should be examined and surveyed for any evidence of unusual localized or overall settlement or depressions.
2. Onsite Inspection Program
(2) Embankment Slope Conditions. Embankment slopes The onsite inspection program of the retention system should be examined and surveyed for irregularities in align- should be established and conducted in a systematic manner ment and variance from originally constructed slopes, unusual to minimize the possibility of overlooking any significant changes from original crest alignment and elevation, evidence features. A detailed checklist should be developed and of movement at or beyond the toe, erosions, and surface followed to document the observations of each significant cracks that indicate movement.
geotechnical, structural, and hydraulic feature, including electrical and mechanical control equipment. (3) Seepage. The downstream face of abutments, em- bankment slopes and toes, embankment-structure contacts, The use of photographs for comparison of previous and and the downstream valley areas should be examined for present conditions should be included as a part of the evidence of existing or past seepage, springs, and wet or inspection program. boggy areas.
The inspection should include appropriate features and (4) Slope Protection. The slope protection should be items, including, but not limited to, the follovlng: examined for erosion-formed gullies and wave-formed notches
3.11.1-3
and benches. The adequacy of slope protection against waves 3. Technical Evaluation and surface runoff that may. occur at the site should be evaluated. The condition. of vegetation or any other types An evaluation of the existing conditions of the retention of protective covers should be evaluated, when pertinent.
system should be made annually unless changing conditions dictate a shorter period. This evaluation should include an
(5) Emergency Discharge Facility. The emergency assessment of the hydraulic and hydrologic capacities, 3 water discharge facility examination should cover the structures and quality, and structural stability and should take into account features, including spillway bulkheads, culverts, retaining both existing conditions and any changing conditions. In walls, and wing walls of diversion channels, for any condition addition, surface water and groundwater sampling data that may impose operational constraints on their functioning. collected in accordance with Regulatory Guide 4.14 should
2 be examined at the time of the technical evaluation to detect
(6) Safety and Performance Instrumentation. All any patterns that could be a sign of failure of seepage con- installed instrumentation such as flow-monitoring weirs, trol measures or foundation distress.
survey monuments, settlement plates or gages, and piezo- meters should be examined and tested for proper function- ing. The available records and readings of these instruments should be reviewed to detect any unusual performance or 4. Inspection Report distress of the structure.
A report should be prepared to present the results of
(7) Operation and Maintenance Features. The main- each technical evaluation and the inspection data accumulated tenance of operating facilities and features (such as pumps since the last report. These documents should be kept at and valves) that pertain to the safety of the retention system the project site for reference purposes, should be available should be examined to determine the adequacy and quality for inspection by regulatory authorities, and should be of the maintenance procedures followed in maintaining the retired only on termination of the project. Any abnormal dam and facilities in safe operating condition. hazardous conditions observed during the inspection should be reported immediately to the NRC staff.
(8) PostconstructionChanges. Data should be collected on changes such as land development or large-scale tree cutting in the watershed area above the facility that have 5. Inspection Personnel occurred since project construction and that might influence the safety of the project. Inspections and evaluations should be planned and conducted under the direction of an experienced professional d. Special Inspection who is thoroughly familiar with the investigation, design, construction, and operation of these types of facilities. At Unscheduled inspections should be performed after each facility, this individual should ensure that all field the occurrence of significant earthquakes, tornadoes, floods, inspectors are trained to be able to recognize and assess intense local rainfalls, or other unusual events. signs of possible distress or abnormality.
2 Immediately following installation or the discovery of an unusual condition, all instrumentation needs more frequent readings than 3
1f additional storage capacity is needed. NRC should be notified quarterly (e.g., daily or weekly) until the patterns of the structural behaviors are stabilized. a year in advance.
3.11.1-4
REFERENCES
1. S.R. Borrowman and P.T. Brooks, "Radium Removal 6. A.O. Babb and T.W. Mermel, "Catalog of Dam Disasters, from Uranium Ores and Mill Tailings," Bureau of Failures, and Accidents," Bureau of Reclamation, U.S.
Mines, U.S. Department of Interior, 1975. Department of Interior, 1968.
7. "Lessons from Dam Incidents, USA," ASCE/USCOLD
2, "Use of Uranium Mill Tailings for Construction Pur- report, 1973.
poses," Hearings Before the Subcommittee on Raw Materials of the Joint Committee on Atomic Energy* 8. R. Dobrey and L. Alvarez, "Seismic Failures of Chilean of the U.S. Congress, October 28 and 29, 1971. Tailings Dams," ASCE Journal of the Soil Mechanics and FoundationsDiv., November 1967.
3. E. Gruner, "Classification of Risk," Proceedings of 9. W.A. Wahler and D.P. Schlick, "Main Refuse Impound- International Congress on Large Dams, Madrid, 1973, ments in the U.S.," Proceedings of the International Vol. 1, pp. 55-68. Congress on Large Dams, Mexico City, 1976.
4. "Summary of Tailing Slurry Release-1972-1977," 10. R.C. Salazar and R.I. Gonzales, "Design, Construction, report prepared by Teknekron, March 1978. and Operation of the Tailing Pipelines and Underwater Tailing Disposal System of Atlas Consolidated Mining
5. E.S. Smith, "Tailing Disposal-Failures and Lessons," and Development Corporation in the Philippines," Pro- Proceedings of the First International Tailing Sym- ceedings of the First International Tailing Symposium, posium, Tucson, Arizona, November 1972. Tucson, Arizona, November 1972.
BIBLIOGRAPHY
"Recommended Guidelines for Safety Inspection of Dams," National Dam Safety Act, Public Law 92-367, 86 Stat. 506 Federal Register, Vol. 39, No. 168, August 28, 1974, and 507, August 8, 1972.
pp. 31334-31346.
"Periodic Inspection and Continuing Evaluation of Completed "Engineering and Design Manual-Coal Refuse Disposal Civil Works.Structures," EM 1110-2-100, Corps of Engineers, Facilities," U.S. Department of Interior, MESA. Prepared Department of the Army, 1973. by D'Appolonia Consulting Engineers, Inc.
"Model Law for State Supervision of Safety of Dams and Reservoirs," U.S. Committee on Large Dams, 1969. "Guidance for Planning of Inspection Programs for Dams,"
USAEC Technical Guide I.H.1, November 1971.
"Statutes and Regulations Pertaining to Supervision of Dams and Reservoirs," Department of Water Resources, "Inspection, Maintenance, and Rehabilitation of Old State of California, 1974. Dams," ASCE, 1974.
3.11.1-5
TABLE 1 URANIUM MILL TAILINGS RELEASES
1959-1979 DATE MILL AND LOCATION TYPE OF INCIDENT REMARKS
8/19/59 Union Carbide Tailing Dike Failure Tailings dam washed out; 'r\ 15,000 T
Green River, UT sands lost to Browns Wash and Green River in flash flood; no increase in dissolved Ra was noted in river.
8/22/60 Kerr-McGee Raffinate Pond 240,000 gal of raffinate released into Shiprock, NM Dike Failure San Juan River; nu 50 x 10-8 pjCi/ml Ra-226; river samples collected several days after release showed no increase in Ra-226 background; river at Medicine Hat (100 mi downstream of plant) showed
0.36 x 10-9 1 iCi/ml Ra-226 on 8/30/60.
12/6/61 Union Carbide Tailing Dike Failure ,u 500 T solids released from tailings Maybell, CO area; 200 T reached unrestricted area;
no liquid reached any flowing stream.
These tailings (offsite) did not constitute a hazard as no persons lived in the area and no drinking water was taken from surface or groundwater in the near vicinity.
6/11/62 Mines Development, Inc. Tailing Dike Failure 200 T solids washed into Cottonwood Edgemont, SD Creek and some carried .25 mi into Angostura Reseroir.
8/17/62 Atlas-Zinc Minerals Slurry Pipeline Est. 280 T solids + 240 T liquids released Mexican Hat, UT Rupture from broken tailings discharge line into draw 1.5 mi from San Juan River. Calcu- lated concentration of river water would have been below 10 CFR Part 20 maximum permissible concentration.
6/16/63 Utah Construction Tailing Dike Material released by 2-ft drainage cut made Riverton, WY Precautionary to prevent cresting due to heavy rains;
Release material released below 10 CFR Part 20
values.
11/17/66 VCA Raffinate Line Est. 16,000 gal of liquid lost because of Shiprock, NM Failure break in raffinate line; material spread over
1/4 acre; break occurred 1 mi from San Juan River with some small amount reaching river.
2/6/67 Atlas Corp. Auxiliary Decant Overflow from main tailings pond over- Moab, UT Line Failure flowed aux. decant system; 440,000 gal lost; average Ra-226 concentration was
5.5 x 10-8 pCi/ml.
7/2/67 Climax Uranium Tailing Dike Failure Dike failure of unapproved retention system Grand Junction, CO released 1-10 acre-ft of waste liquid into Colorado River; no indication that Ra conc.
in river exceeded 10 CFR Part 20 limits.
3.11.1-6
TABLE 1 (Continued)
URANIUM MILL TAILINGS RELEASES
1959-1979 DATE MILL AND LOCATION TYPE OF INCIDENT REMARKS
11/23/68 Atlas Corp. Slurry Pipeline 35,000 gal of tailings slurry lost; effluent Moab, UT Rupture flowed down drywash and then 1/2 mile to Colorado River; riverflow sufficient to give
10,000: 1 dilution; most solids settled out in drywash; measurement of river down- stream of plant immediately after release and at 4-hr intervals in 24 hr following release showed U, Ra-226, Th-230 below
10 CFR Part 20 limits.
2/16/71 Petrotomics Secondary Tailing 2,000 gal of liquid lost to unrestricted Shirley Basin, WY Dike Failure area; break in dike of effluent sump;
spill frozen in place.
3/23/71 Western Nuclear Tailing Line-Dike Break in sand tails slurry line caused a dike Jeffrey City, WY Failure failure allowing sand tails to flow for 2 hr into natural basin adjacent to tailings site on licensee's property; fence extended to make this area restricted.
2/5/77 United Nuclear- Slurry Pipeline Tailings slurry pipeline ruptured by high Homestake Partners Rupture pressure buildup in a frozen line. The Grants, NM slurry released eroded a "V" cut in the dam
-_ -- I face, which led to the escape of approxi- mately 50,000 tons of solids and slimes and somewhere between 2 million and 8 million gal of liquid. All material released was confined to company property.
4/77 Western Nuclear, Inc. Failure of Tailing Tailings slurry overtopped the embankment Jeffrey City, WY Pond Embankment because of insufficient freeboard space, considerably less slope than the requisite 3 horizontal to 1 vertical, and a loss in struc- tural integrity caused by the melting of snow interspersed with the fill used to construct the embankment. 'u 2 million gal of liquid tailings (55 yd 3 of solids) were released. The grind mill and mill yard were completely covered, but no material was released to unrestricted areas.
9/26/77 United Nuclear Release from In the process of flushing tailings lines, it
9/27/77 Church Rock, NM Tailings Slurry Line was discovered that a 2-inch water line had insufficient pressure to flush out plug. The line was uncoupled and roughly 1/4 ton of tails ran out of the line. Width the line still uncoupled, flushing was inadvertently initiated again, resulting in the release of
4,000 gal of flush water and an additional ton of tailings. Approximately I ton of solids and slurries and 900 gal of liquid entered the watercourse. The liquid flowing to the watercourse was almost entirely mine water, a portion of which had not been treated (i.e., high in uranium and radium values).
3.11.1-7
TABLE 1 (Continued)
URANIUM MILL TAILINGS RELEASES
1959-1979 DATE MILL AND LOCATION TYPE OF INCIDENT REMARKS
7/16/79 United Nuclear Tailing Dike The tailings embankment failure was a Church Rock, NM Failure result of internal erosion of the embank- ment caused by a combination of two factors. Differential settlement occurred in the foundation materials underlying the embankment and resulted in cracking of the embankment. In addition, tailings liquid was allowed to come into direct contact with the embankment near the area eventually breached. The flow of liquid through the cracks resulted in the internal erosion of the embankment and the eventual breach. The breach resulted in the release of approximately
100,000,000 gallons of tailings solution and 1,100 tons of tailings solids. Though most of the solids were deposited near the impoundment, much of the solution reached the Rio Puerco. Cleanup actions were undertaken and use of the river water for livestock watering was restricted pending reduction of contaminant levels.
The river water is not used for human consumption.
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