ML20214V870
| ML20214V870 | |
| Person / Time | |
|---|---|
| Issue date: | 05/31/1987 |
| From: | NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | |
| References | |
| NUREG-1245, NUREG-1245-V01, NUREG-1245-V1, NUDOCS 8706120346 | |
| Download: ML20214V870 (62) | |
Text
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.s NUREG-1245 Vol.1 Radioactive Waste Management Research Program Plan for High-Level Waste 1987 U.S. Nuclear Regulatory Commission Of fico of Nuclear Regulatory Resourch
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NOTICE Availability of Reference Materials Cited in NRC Publications Most documents cited in N RC publications will be available from one of the following sources:
- 1. The NRC Public Document Room,1717 H Street, N.W.
Washington, DC 20555
- 2. The Superintendent of Documents, U.S. Government Printing Office, Post Office Box 37082, l
Washington, DC 20013 7082
- 3. The National Technical Information Service, Springfield, VA 22161 Although the listing that follows represents the majority of documents cited in NRC publications, it is not intended to be exhaustive.
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American National Standards institute,1430 Broadway, New York, NY 10018.
NUREG-1245 Vol.1 Radioactive Waste Management Research Program Plan for High-Level Waste 1987
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ABSTRACT i
The program of research described in this plan is intended to identify and resolve technical and scientific issues involved in the NRC's licensing and regulation of disposal systems intended to isolate high level hazardous radioactive wastes (HLW) from the human environnent.
The Plan describes the program goals, discusses the research approach to be used, lays out peer review procedures, discusses the history and development of the high level radioactive waste problem and the research effort to date and describes study objectives and research programs in the areas of:
a.
Materials and engineering i
b.
Hydrology and geochemistry c.
Compliance assessment and modeling The plan also details the cooperative interactions with international waste l
management research programs.
In addition, a proposed Earth Scierice Seismotectonic Research Program plan for radioactive waste fact 11 ties is appended.
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Foreword I
This document presents a plan for high level radioactive waste management I
research to be performed and managed principally by the Waste Management Branch, Division of Engineering, Office of Nuclear Regulatory Research.
4 It presents the objectives of the program, describes the research that will be j
carried out to achieve the objectives, and identifies areas of cooperation and/or coordination with research being performed by other organizations. This plan should be examined in conjunction with the similar and complimentary Low Level Waste Plan, NUREG-1246.
We intend and expect to revise these plans periodically to take into account the results of the research projects, our experience in implementing the plan, changing Agency directions and needs and desires of Congress, the States, applicants and the public as well as comments from interested parties within and outside of the NRC.
Comments on these documents are welcome at any time and will be considered in the development of subsequent editions of these plans. Comments need not be restricted to the research areas described here; comments and suggestions identifying omissions or recommending additional research are also welcome.
1 Approved By:
Frank A. Costanzi, Chief Waste Management Branch Division of Engineering Office of Nuclear Regulatory Research 1
LIST OF ACRONYMS Abbreviation Term AEC Atomic Energy Commission CEC Commission of European Communities DOE Department of Energy DOI Department of Interior DE Division of Engineering, RES EBS Engineered Barrier System EPA Environmental Protection Agency FFRDC Federally Funded Research and Development Center HLW High Level Waste HLWM Division of High Level Waste Management, NMSS LLW Low Level Waste LLWM Division of Low level Waste Management, NMSS NRC Nuclear Regulatory Commission NMSS Office of Nuclear Material Safety and Safeguards, NRC RES Office of Nuclear Regulatory Research, NRC SCRB Senior Contract Review Board SSEB Structural and Seismic Engineering Branch, RES USGS United States Geological Survey WMB Waste Management Branch, DE, RES WMRG Waste Management Review Group 3
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l TABLE OF CONTENTS 4
fase iii ABSTRACT................................................................
1 FOREW0RD...............................................................
3 LIST OF ACR0NYMS........................................................
l 5
l TA B L E O F C 0 NT E NT S.......................................................
7
1.0 INTRODUCTION
9 2.0 PROGRAM G0ALS......................................................
)
3.0 RESEARCH APPR0ACH..................................................
10 4.0 PEER REVIEW........................................................
14 5.0 WASTE TYPES / GENERAL DISCUSSION.....................................
16 5.1 High Level Waste (HLW)........................................
16 5.1.1
Background
5.1.2 History of RES's HLW Research Program 5.1.3 Present and Future Directions 5.2 Low Level Waste (LLW)..(See NUREG 1246 for discussion)........
20 6.0 TECHNICAL AREAS / SPECIFIC RESEARCH..................................
22 6.1 Materials and Engineering Study Objectives....................
22 6.2 Hydrology and Geochemistry Study Objectives...................
25 6.3 Compliance Assessment and Modeling Study Objectives...........
P6 6.4 Earth Science /Seismotectonic Research.........................
30 7.0 OTHER RESEARCH AREAS...............................................
32 5
8.0 COORDINATION WITH INTERNATIONAL WASTE MANAGEMENT RESEARCH PROGRAMS... 33 Appendix: Proposed Earth Science Seismotectonic Research Program Plan for the Siting of a HLW Reposi tory...........................
35 6
1.0 INTRODUCTION
Disposal of radioactive wastes has been a concern throughout the world for many Discussion and debate as to the best methods of accomplishing suffi-years.
cient isolation of these hazardous materials was begun in the early days of nuclear utilization and continues today.
Involved are not only technical and scientific questions of fact, but serious and legitimate questions of social concern.
The Atomic Energy Comission (AEC), Nuclear Regulatory Comission (NRC),
Environmental Protection Agency (EPA), Department of Energy (DOE), Congress, scientific and public interest groups have considered this subject for almost 40 years, trying to balance actual hazard against perceived hazard; costs against benefits; method against method. As this debate lengthened it became apparent that the state of knowledge was limited on the basic physical, chemical and mechanical processes that detennine the behavior of radioisotopes placed in isolation over the very long time periods during which they would retain some degree of hazard. Mankind has never before attempted to isolate hazardous materials in the earth for as long as radioactive materials must be isolated nor to accurately predict, so far into the future, the consequences of these actions Radioactive wastes are broadly characterized as high-level waste (HLW), trans-uranic wastes (TRU), low-level waste (LLW) and uranium mill tailings (uranium recovery - UR). HLW primarily originates from fuel removed from nuclear reac-tors. This, and other radioactive wastes originates from five major sources:
- 1) the fuel cycle of commercial nuclear reactors; 2) defense programs; 3) medical and research institutions (e.g., hospitals, universities, and research organizations); 4) industrial uses; and 5) the mining and milling of uranium In the future, large quantities of waste can be expected from the ore.
decomissioning of nuclear facilities and remedial actions conducted by the D0E. The first two sources will produce almost all of the HLW that will require disposal in deep geological repositories for very long time periods.
All of these sources will produce the remainder, broadly termed LLW, which requires isolation for a lesser, though still long, time period.
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This Radioactive Waste Management Research Program Plan for High Level Waste is designed to assist NRC in meeting its obligations under the Atomic Energy Act and any subsequent legislation addressing high level radioactive wastes. A 4
separate Program Plan, NUREG-1246, addresses the research activities needed to meet NRC obligations for low level radioactive waste disposal safety. This LLW Plan should be viewed as complimentary to the HLW Plan as there is a great deal of overlap of the scientific disciplines and technical bases for the safe isolation of both waste types.
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d 2.0 PROGRAM G0ALS:
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1.
To identify, characterize, and contribute to the eventual resolution i
of problems involved in the processes and phenomena that control containment and/or movement of radionuclides from a high level radioactive waste repository to the human environment.
2.
To identify all important repository performance parameters and processes and to understand the reason for each factor's significance during the various time periods of a repository life.
3.
To identify and quantify uncertainties and the safety implications of uncertainties and to contribute to the eventual resolution of those uncertainties deemed significant.
4 To quantify, where possible, the benefit to public safety from the addition of incremental engineered systems or management technioues to repositories.
5.
To identify and rank in order of importance those aspects of high level radioactive waste management that could significantly alter ultimate safety impacts to the public if assumptions are in error.
By concentrating efforts on those areas that could make a significant difference, our resources will be used most economically.
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3.0 RESEARCH APPROACH NRC is the agency charged with licensing and regulating disposal of HLW. NRC's task is to establish and implement the framework for oversight and review of all aspects of HLW disposal facility siting, design, construction, operation and closure, to assure that radioactive waste disposal presents no undue risk to the public health and safety or the environment.
The goal of NRC's waste management research activity is to assure sufficient breadth and technical soundness of the regulatory framework and the staff's analytical capability to carry out the regulatory mission of the agency. HLW research is carried out by the Office of Nuclear Regulatory Research (RES) and the results are provided to the Office of Nuclear Materials Safety and Safe-guards (NMSS) which performs the regulatory reviews and provides guidance to the licensee, and the Department of Energy (DOE).
While all aspects of scientific research that add to our understanding and appreciation of the world around us are of value, regulatory research must be focused exclusively on projects that assist the agency to carry out its mission effectively and efficiently. Hence, HLW regulatory research investigates unassessed sources of repository failure, assesses the nature and magnitude of uncertainties associated with predicting-facility performance, provides the technical bases and specific analytic tools to support NRC's independent review of DOE's licence application and DOE's demonstration of compliance with regu-latory requirements. The choice of what specific research projects to under-take is made in a carefully structured manner involving continuing collegial discussions between NMSS and RES staff and management.
I To help focus regulatory research the following criteria have been useful in identifying research of regulatory importance. To be considered as regulatory research, the research must be needed to:
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1.
Develop expertise in an unfamiliar technology that must be used for high radioactive waste disposal.
The scientific and technical disciplines involved in the successful geologic disposal of HLW are extremely varied and, often,- the understandings of specific technical issues are not well developed.
Research is needed to develop the working body of knowledge of those successful geologic disposal of HLW physical, chemical, and mechanical
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processes and phenomena important to waste disposal and their interactions, especially theLinteraction of engineered components of the t
disposal system with the natural environnent.
or 2.
Assist in performing audits of testing or analysis submitted by the DOE seeking a license to dispose of high level radioactive wastes in a geologic repository 4
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Research to produce assessment models used to test the predicted of a radioactive geologic repository is needed to. assist the staff to under-stand, evaluate and judge the competency of testing and analysis done by DOE for site characterization, safety and environmental analyses.
Research is needed to identify, quantify, and reduce uncertainties in the assessment of expected repository performance.
Research also is needed to develop the tools to apply the broad understanding to the specific regulatory issued and decisions involved in licensing and regulatory geologic disposal of HLW.
or 3.
Develop regulatory tools such as regulations, guides standards, general design criteria, staff technical positions, etc. that will be used to evaluate or guide DOE HLW disposal activities.
A framework of regulations and guidance that is reasonable, understandable and usable has been established. Past research has provided significant technical support for those regulatory guides. As the development of DOE's program proceeds, and issues appropriate for rulemakings or other guidance are identified, further research will be conducted to support the rulemaking or other guidance activities, as appropriate.
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Further, the research program must fit the overall licensing strategy for research, i.e., the research must have one or more of the following purposes:
1.
Establish and document our present technical understanding.
2.
Identify facility performance issues.
3.
Develop assessment methods.
4.
Identify information needs.
5.
Establish, evaluate, or assess test plans and procedures.
6.
Generate data needed for an independent review of models, assumptions, initial and boundary conditions.
7.
Determine areas of uncertainty.
8.
Quantify the range and significance of uncertainties.
9.
Provide a basis to reach findings on specific technical issues.
There are a few principles, or assumptions, that will guide the RES staff throughout the waste management research effort. They are, perhaps, too obvious to require long discussion. However, since they form a framework upon which all involved will base future actions, they deserve to be listed:
1.
The citizenry of the U.S. is deeply and legitimately concerned about the safe ultimate disposal of radioactive waste for their protection and the protection of future generations.
1 2.
The Congress has mandated the timetable and the legal framework for the accomplishment of safe disposal of HLW by the DOE.
3.
It is the legislated responsibility of the NRC to assess independently the safety and compliance with pertinent I
regulations of the DOE's geologic disposal activities, and determine whether DOE has provided reasonable assurance of safety and compliance.
4 The technical basis for licensing decisions, and all assumptions contained therein, will be subjected to intense and close scru-tiny, not only during the near term but for generations to come.
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Staff and other'" institutional" memory is fallible and transitory. Accurate, step-by-step documentation of the i
f information base supporting licensing work and decisions is i
crucial so that future reviewers can reconstruct what has been 4
done.
5.
The role of RES is to carry out the research that provides the technical support and the regulatory tools that the user Office (primarily NMSS) needs in order to carry out its responsibilities.
6.
The resources, funds and staff available for waste management research are extremely limited. Every effort must be made first to identify those issues that affect safety and then to apply RES resources in the most efficient manner to resolve those most
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critical issues.
7.
NRC research efforts must be _ focused on identifying significantL uncertainties and in scoping reasonable investigative approaches l
that can be used by applicants in reducing these uncertainties I
to acceptable levels. Limited resources will, by and large, preclude NRC from resolving many of the open questions. Final resolution must be left to the applicant, subject to regulatory review.
8.
Each research project, to the extent possible,_must be so structured as to have a clearly identified end point.
In other words, the project must be designed to require the answering of 4
specific questions and/or to develop concrete and usable techniques within a given. time period for a specified cost.
Projects must not be allowed to be too broad in scope nor.their objectives open ended. Otherwise, their practical utility for regulatory research will be diminished and the costs will escalate.
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4.0 PEER REVIEW The independent critical evaluation of research by unbiased contemporaries, conversant in the technical areas involved, is an integral part of any well designed and robust scientific inouiry. This process of collegial self review occurs, usually, as a normal and expected part of both the informal and the formal interchange that goes on in any scientific discipline.
In a program such as that of the management of radioactive waste with its attendant impli-cations for public health and public confidence in the regulatory process, this process of critical examination cannot be allowed to be either casual or less than rigorous, t
Peer review, by its very nature, implies the open and forthright exchange of infomation, experience and comment between technical and professional equals.
It does not imply an adversarial or oversight role by the reviewer. Partici-pants in this process should understand that their peers will approach the review with the intent of providing coments that will aid the researcher in producing better research. The review must be so conducted that it is a valuable adjunct to the program and not a hurdle to be surmounted.
The NRC program of radioactive waste management research has always been subject both to the tests of review by staff, management and internal and external review bodies and to the research peer review. This peer review process has now been expanded and fortnalized to require formal contractual peer review by external, independent, individuals and bodies. This formalized review by competent peers in the scientific community will be conducted on both
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the project and the program levels.
Project Level Peer Review:
Beginning in FY 87, during the planning of research, each Project Manager will select at least one technical peer from the scientific community to follow the contracted work as it progresses and to critically assess the rigor of the
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science utilized by the investigators. This review will direct attention to the theses and methods of the research project and will examine periodically the course of the research. The reviewer will consult closely with the Project i
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9 Manager, meet occasionally with the principal investigators of each project reviewed, and will be expected to attend and participate in selected research meetings and symposia at which the results of the project are presented and discussed. Periodic reports will be submitted to the NRC Project Manager who will inform supervision of the status and results of the review, and recommend, as appropriate, changes in the direction and conduct of the project.
Provisions for this peer review procedure will be included in FY 88 statements of work for each contract initiation in FY88.
HLW Programmatic Completeness Review:
i About two or more years prior to the NRC's anticipated receipt of a I
construction authorization application from DOE, a HLW Programmatic Waste Management Research Completeness Review will be contracted by NRC to an l
independent outside body. Such groups as the American Physical Society, National Academy of Sciences, National Research Council, National Academy of 1
Sciences, etc., will be considered for this function. The review body will be l.
directed to assemble a group of technical peers to critically examine the concepts, design of experiments, methodology, analytical and decisional techniques, data quality, statistical validity, completeness and findings and j
conclusions of the HLW research work sponsored by NRC. The review will be l
expected to examine published results and data presented by the investigators j
or RES project managers, as appropriate, and to make appropriate inquiry of the principal investigators.
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5.0 WASTE TYPES / GENERAL DISCUSSION Congressional legislation and the NRC regulations have divided nuclear waste into three broad categories, High-level Waste (HLW), Low-level Waste (LLW) and Uranium Recovery Waste (UR). For budgetary and programmatic reasons, NRC is no longer conducting research on UR disposal. A discussion of the legislation, regulations and technical uncertainties for HLW only follows. This discussion should be helpful in understanding the regulatory research requirerrents of HLW disposal. Because the basic chemical and physical processes that effect isolation of radioactive wastes are often common to both HLW and LLW, NRC's waste management research projects are organized by technical area to take full advantage of the commonality of technical issues. This approach provides a well ir,tegrated and effective waste management research program for both high and low level wastes. Nonetheless, for the sake of clarity only HLW research will be discussed in what follows.
5.1 High Level Waste 5.1.1
Background
The design of the NPC's High Level Radioactive Waste Research Program has been driven by the disposal method required by the Nuclear Waste Policy Act and addressed in the NRC's regulation 10 CFR 60, i.e., disposal in deep geologic repositories, and the requirements for safe disposal as embodied in the legislation and regulations within which the NRC must operate:
the Atomic Energy Act, the Energy Reorganization Act, the Nuclear Waste Policy Act of 1982, the EPA HLW standard (40 CFR Part 191),
and the NRC HLW regulation (10 CFR Part 60). The legislation and regula-tions require the NRC to make licensing findings concerning public health and safety and environmental release for periods up to 10,000 years and distances measured in miles. These findings, in part, will be based upon NRC's review of DOE's predictions of:
- 1) performance of engineered barriers, 2) radionuclide release and transport through a heat affected (thennally disturbed) zone, and 3) radionuclide transport through a relatively undisturbed zone to the environment.
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The basic key to confident regulatory decision making regarding geologic disposal of HLW is knowledge and understanding of how the geologic environment will respond over long periods of time ( 10,000 years) to the emplacement of wastes, and in turn how the engineered systems which are part of the geologic disposal scheme will behave in the geologic environ-I ment in which they are placed. However, at this time, the ability to make confident predictions of repository behavior over 10,000 years is very limited. Some reasons for this are discussed below.
4 1.
Sites under consideration by DOE for a repository are in salt or in what are believed to be low-flow hydrologic systems. Such 1
systems have received little attention from the commercial sector because the yields of commercially valuable fluids 4
(including potable water) or gases from low permeability rock are ccmmercially unattractive.
The research which has been l
conducted on such systems has addressed the question of how to increase flow (e.g., hydro-fracturing) to tap resources rather i
than how to predict flow and maintain low flow conditions.
For j
salt formations, aside from oil storage, economic interest has
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focused attention on the mining of salt. Hence questions of l
stability, the rate of interbeds, and salt dissolution have all i
been addressed only from a short-term mining operation per-j spective. Moreover, until recently, the effects of thema11y l
hot emplaced wastes on salt have not been considered outside of some very early work done by the AEC at Lyons, Kansas.
2.
The geochemistry of transport in the thermally disturbed area is i
extremely complicated and relatively unknown. Much of the information developed by DOE comes from data obtained from i
laboratory measurements of radionuclide adsorption on crushed rock, much of which has been observed to be irreproducible.
Further, the literature contains little on the behavior of radionuclides in geologic environments at the elevated temperatures expected at a repository, d
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Engineered structures have not.been built at the depths at which repositories will be located or to function for the very long time period over which a repository will be required to isolate 1
emplaced wastes. Further, there is no way to directly test the performance of these structures over their lifetimes. Hence relatively short cerm laboratory tests will provide the only observational base to assess the performance of the structures and materials comprising the engineered barrier systems (EBS) at the elevated repository temperatures, in high radiation fields, in a hostile environment, over the long times required. This situation leads to considerable uncertainty in estimatino the rates and amounts and chemical and physical form of the release l
of radioactive and other materials from the engineered barrier system to the natural barrier systems. Moreover there are also
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great uncertainties related to the combined thermomechanical
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effects of the emplaced waste on the transported fluid flow rock j
properties and on the stability of repository openings which-impact the capability of maintainina the option of waste retrieval.
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The NRC HLW research program is aimed at understanding the phenomena which control the containment, release, and transport of radionuclides from a l
repository facility at depth. The NRC does research, not to fill'in the j
knowledge gaps, per se, but rather to probe the bounds of uncertainty to j
be able to judge whether DOE has taken account of all the relevant processes and phenomena in their demonstration of repository behavior.
In short, the NRC HLW research program has two overall goals: 1)to understand what makes a geologic repository work or fail, and 2) to determine what constitutes an adequate technical demonstration that it j
will work.
4.1.2 History of RES's HLW Research Program Bef re discussing the specifics of the HLW research program it would be useful to characterire the present status of the program through a bit of-history. Early NRC research programs in HLW were underway in the mid i
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1970's. These were general at first and then (prior to about 1981) became centered around development of risk assessment methodology for geologic disposal of HLW in salt. The impetus for this focus was two-fold.
First was the anticipation that the EPA HLW standard would be risk-based and implemented by conducting a risk assessment. Second was the preference by DOE for salt as the host medium.
The results of that early research, as well as the course of technical and political events, pointed out that:
- 1) a risk assessment on something both new and unique as a geologic repository was far too uncertain to alone provide the degree of confidence in expected performance required for sound regulatory decision making; 2) that salt would not necessarily be the host medium of choice. Hence, around 1981 the HLW research program underwent a major change in direction, branching out into a number of specific scientific disciplines to identify and describe the processes and phenomena that make a repository work - i.e., provide long tenn isolation i
of the wastes. Along with this realignment came research aimed directly at the development and support of NRC's HLW regulation, 10 CFR Part 60.
Tracking DOE's program, NRC's HLW research over the past five years has focused basalt and (to a lesser extent) tuff as additional potential host media. At present the program is concentrating on tuff and salt; basalt, tuff and salt being the three media under consideration for the first repository. Present efforts are intended to bring the level of effort in the tuff and salt media closer to the level reached in basalt.
Funding limitations have prevented concurrent equal research programs on basalt, tuff and salt. Further, recent budget reductions have forced premature termination of the basalt research, further delays in the salt related research and indefinite deferral of work on granite for the second re-pository. However, some balance is achieved in that funds are being expended almost equally on (1) materials and engineering (waste fonn properties, overpack failure modes, and properties of backfill and seals),
(2) the geochemistry of radionuclide transport, and (3) identifying the essential elements of system models of the flow of grourdwater and trans-port of radionuclides in fractured rock (saturated and unsaturated).
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5.1.3 Present and Future Directions The NRC's HLW research program is now undergoing another transition. The research results obtained so far have concentrated on identifying the processes and phenomena important to repository performance. Thereby, the research results have provided technical support to the NMSS licensing staff's interactions with DOE, including review of DOE's environmental assessments (EA's), and will support their review of DOE's site characterization plans and activities. The program is now shifting to deepen the staff's understandings of both the processes and phenomena important to safe geological disposal of HLW and the interactions among them. As the previous phase of the program will facilitate NRC's judge-ment of whether DOE has considered all relevant processes and phenomena in i
their site characterization plans, so this next phase will facilitate NRC's review of how well DOE addressed those processes and phenomena in carrying out site characterization - i.e., the adequacy of data, measure-ments and analyses supporting DOE's construction authorization-application.
There is a final phase of HLW regulatory research that will begin with repository construction. That phase will focus on key site specific j
characteristics of performance demonstration, especially the performance j
conformation program required of DOE by 10 CFR Part 60. That phase also will address those specific issues left unresolved at construction authorization and will help provide the technical background for ultimate closure decision. Planning for the specifics of that final phase will not f
begin for several years.
5.2 Low Level Waste 4
Due to the differing legislation governing NRC's approach the regulation i
of high and low-level radioactive waste, as well as a changing organizational structure within NRC to reflect these differing requirements and approaches, it has been decided to cover the staff's research approach for each waste type in separate volumes. This will also make it more convenient and varied to revise the documents as research 20
h needs and priorities change. For a detailed discussion of the Waste Management Branch Low-Level Radioactive Waste Research Program Plan, see
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the complimentary publication, NUREG-1246.
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6.0 TECHNICAL AREAS / SPECIFIC RESEARCH In order to implement a comprehensive research program that will be applicable I
to understanding the management of both HLW and LLW, the specific studies must be categorized so that they address understanding the application of the basic chemicel and physical processes that govern the disposal of any material in the earth, no matter what the material's classification. Most waste management i
research can thus be described by placing it into one of three categories i.e.,
- 1) " Materials and Engineering," which examines the techniques used in assessing designs that are intended to contain the radionuclides within the waste package or waste fonn, 2) " Hydrology and Geochemistry", which studies the basic processes that determine the movement and/or retention of radionuclides in the earth, and 3) " Compliance Assessment and Medeling", which focuses on the issue of confidence in judging the adequacy of DOE's demonstration of safety and compliance with NRC and EPA requirements.
l The radioactive waste management research program is organized into the cate-gories described above. Our research examines basic processes that, by and large, are comon to both high and low level waste isolation. Although it would be reasonable to list and discuss each individual research program in a general Program Plan such as this, without regard to whether focus is HLW or
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LLW, it is somewhat impractical. Therefore, this NUREG will address only those programs which emphasize study of HLW issues, with the exception of programs which apply equally to both, which will appear both in this NUREG and in the companion LLW program plan, NUREG 1246. Excluding LLW programs is in no way intended to indicate a restraint on the utility of much of the LLW research to the HLW program.
6.1 Materials and Engineering Study Objectives Materials and Engineering studies are conducted to explore the relationship among waste package materials, waste forms, engineered features of the disposal facility, and the disposal facility environment.
These studies furnish the staff with the technical basis to be able to assessindependently,1)whetherclaimedperformanceofwastepackage, 22
_ _. _ _, _ _ _.. _ _ _ _ _ - _ - _.. _ - _ _ _ - - -. _ _ - - ~ _.
waste fom, and other engineered components of the disposal system is i
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consistent with the materials and methods of manufacturing and l
construction, 2) the suitability of tests and demonstrations of expected
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perfomance, and 3) compatibility of the waste package, waste form, and other engineered features with expected disposal environments.
Descriptions of specific research topics follow.
l 6.1.1 Studies are performed to assess the applicability and reliability of various analytical and test methods used to extrapolate short tem laboratory test results to long term expectations of waste
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package materials and design perfomance. This work supports the NRC l
l staff's independent assessment of the validity of an applicant's testing, f
measurement, and analytical techniques for making long tem extrapolations
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for containment of both high and low level radioactive wastes.
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i 6.1.2 Programs are conducted to assess the applicability and l
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reliability of various analytical and test methods used to extrapolate short tem laboratory test results to long tem expectations of waste form
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performance. This work will support staff's independent assessment of the l
validity of the testing and measurement techniques for determining the l
i expected long tem perfomance of both high and low level waste foms.
l The work also supports the development of source term assumptions to be used in the modeling programs.
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i I
l 6.1.3 Studies are being perfomed to determine the effects of various j
fabrication processas on the corrosion and mechanical properties of the f
i HLW waste package container materials.
Fabrication processes under
}
evaluation include chill casting and submerged-arc and electron-beam l
welding. The results of these studies are intended to facilitate the f
staff's assessment of waste package perfomance and give them the tools
(
f needed to independently evaluate the suitability and effectiveness of an l
applicant's Quality Assurance /00ality Control procedures; i.e., whether i
l the performance of the waste package (as built) will be consisterit with I
l the claimed performance of the waste package (as designed).
I i
23
6.1.4 Projects are being perfomed to explore the relationship among disposal facility design features, construction techniques, waste package environment, and test and measurement methods so as to characterize the waste package and disposal environment. This will provide the staff with the ability to make an independent comparison of claimed disposal environment and the actual facility design and construction for both HLW and LLW disposal facilities.
6.1.5 Field and laboratory experiments under the project " Sealing of Boreholes and Shafts in Salt " assesses the effectiveness of sealing man made penetrations in salt (halite), a geological formation being considered as host rock for HLW disposal. Major uncertainties continue to exist with regard to the mechanical behavior of salt, especially salt creep. Since this in turn affects salt sealing effectiveness, the work hopes to resolve several issues about the performance and design of borehole and shaft seals for salt repositories.
6.1.6 In order to obtain an understanding of the degradation of the metallic containers of HLW, the NRC HLW research program is supporting efforts on corrosion in the projects "Long Term Performance of Materials Used for High-Level Waste Packaging," " Pitting Corrosion Chemistry," and
" Statistics of Package Failure by Pitting." In these projects, pitting corrosion has been identified as a major fonn of degradation of metallic containers that is in need of additional research. The NRC HLW research projects on pitting corrosion have shown that pitting corrosion can happen in HLW packages and can penetrate through metallic containers more rapidly than uniform corrosion. Stress corrosion cracking also has been identi-l fied as a likely mechanism by which metallic containers of HLW can fail, i
There are no existing models of stress corrosion cracking that are adequate for application to predicting HLW repository performance.
This work has been focused on the basalt environment.
In FY87 the corrosion program is shifting its focus to the salt environment with five new projects aimed at assessing corrosion problems in salt by 1992.
In FY88 a similar assessment of corrosion problems in the unsaturated tuff 24
environment will begin. This work will provide additional independent capability for the staff in making its regulatory decisions.
I 6.2 Hydrology and Geochemistry Study Objectives 6.2.1 Research projects are being conducted to explore the behavior of groundwater in fractured saturated and unsaturated geologic media. This work is directed at identifying issues and parameters essential to devel-oping sound and reviewable descriptions of groundwater and radionuclide movement in these zones. This is particularly applicable to HLW repositories. This information will allow the licensee's staff to more reliably model HLW repository performance.
6.2.2 Studies are underway to develop an understanding of the l
l competing chemical and physical processes that determine radionuclide l
mobility and availability for migration in thermally undisturbed environments. These studies will facilitate independent assessments of the correspondence of laboratory tests to " field" expariments with respect to the movement of radionuclides in groundwater systems. This information l
will be useful for evaluation of both HLW and LLW disposal.
6.2.3 Programs are underway directed at identifying and enhancing the hRC staff's understanding of the competing chemical and physical processes that determine radionuclide mobility and availability for migration in i
thermally disturbed environments adjacent to HLW repositories. These studies are employing the available data from natural hydrothermal systems to provide insight into the expected geochemistry and hydrology in close proximity to the HLW emplacement area and to establish the correspondence among laboratory experiments and in-situ repository experiments and i
expected long-term repository performance.
6.2.4 Studies to explore methods to characterize past climates will be continued. These studies provide the tools needed by the staff to independently assess the required range of potential future climatic changes against which HLW repositories or LLW waste disposal facilities must be evaluated.
25
l i
4 6.3 Compliance Assessment and Modeling Study Objectives Compliance Assessment Modeling research explores the uncertainties l
associated with modeling the performance of both individual disposal l
facility components and systems and the overall disposal facility. These studies will facilitate the staff's independent assessment of the DOE's demonstration of the perfomance of its proposed facility with respect to meeting applicable environmental standards, and meeting the specific performance objectives of 10CFR Part 60. These modeling studies are needed because prototypical tests cannot be done to proof test repository
]
perfomance over the very long time periods involved.
Several lines of inquiry are and will be carried out by the WMB to gain confidence in the use of models and the assumptions that go into them, and to facilitate the l
NRC staff's judgment as to the adecuacy of the DOE submittal in support i
of its licensing application. These lines of inquiry are in three general i
areas. Firstly, we are examining currently available scientific results.
a fair amount of which comes from our phenomenological waste management I
research. Secondly, we are developing laboratory tests that are analogous j
to or dynamically similar to selected HLW repository situations. Thirdly, 7
l we are studying relevant " natural analogues," 1.e., natural geologic i
l processes and events that are similar or analogous to aspects of reposi-I tory perfomance. Specific research topics include:
I, -
6.3.1 Research studies are underway to explore methods of making phenomenological models of the movement of ground water in fractured media.
1 These studies aid the staff by providing an independent technical basis i
for assessing the consistency of DOE's description of the hydrological characteristics of proposed repository sites in saturated fractured media.
l This will, in turn, allow the licensing staff to make informed judgments l
with regard to basalt and crystalline rock media.
j 6.3.2 Similar research programs are investigating the phenomonology of the movement of ground water in unsaturated fractured media. This work facilitates the staff's independent assessment of the adequacy of the DOE l
submittal for licenses for repositories located in these geologic media.
i 26 i
This will allow the licensing staff to make informal judgments for tuff site media.
l l
6.3.3 Programs are being conducted to explore the effects of the I
themal perturbation that the heat of radioactive decay of waste will have upon the perfomance of a HLW repository. This research is producing a technical basis which the staff can use in its independent review of whether the DOE has taken into account the coupled mechanical, chemical, and hydrologic effects of the themal loading from the waste emplaced within the repository.
6.3.4 A major natural analogue project "Radionuclide Migration Around Uranium Ore Bodies - Analogue of Radioactive Waste Repositories,"
has been active since 1981. This project is being conducted by the Australian Atomic Energy Commission at the Koongarra ore body in Australia, involves an effort to validate the mathematical models of radionuclide transport models such as that embodied in the computer program SWIFT, prepared for NRC by Sandia National Laboratories. The current stage of this project ends in FY87.
Follow-on work is being planned as a multi-national effort in which NRC intends to actively participate. This, and other, natural analogue studies will increase the NRC's knowledge of how natural systems may relate to the perfomance of a repository over long time periods.
6.3.5 Another project involving the consideration of data from natural analogues is " Investigation of Ccupied Interactions in Geothermal and Hydrothemal Systems for the Assessment of HLW Isolation," at the Lawrence Berkeley Laboratory (LBL). The objective of this project is to provide NRC with an understanding of the coupled interactions that are likely to have a significant effect on the performance of a geologic repository, especially during the initial period during which significant heat is generated by the waste, by drawing from investigations of coupled interactions in geothermal systems and determining whether and under what conditions similar interactions are important to the behavior of an HLW repository.
27
~ _ _ _ _ _ _ _ _ _ _ _ _ _ _
4 2
{
6.3.6 In addition to managing projects involving natural: analogues.
l the WMB staff will continue to participate in natural analogue workshops j
sponsored by other domestic and international agencies such as those l
sponsored by the Conunission of European Communities (CEC) that are also
]
considering the interrelationship of natural systems and our understanding l
of how hazardous waste disposal technologies may perfonn over the long f
time requirements.
i i
j 6.3.7 The recently begun project, " Flow of Ground Water and Transport j
j of Contaminants through Saturated Fractured Geologic Media from High-Level
)
Radioactive Waste" will examine the validity of dispersion theories, the j
identification of regimes (porous, doubly porous, discrete fracture, etc.)
{
in saturated fractured rocks, field identification of matrix diffusion, I
and the use of groundwa'ter dating data for calibrating flow and transport models. This will supply the licensing staff with tools needed to independently judge the validity of the assumptions and modeling
)
techniques used by DOE.
l 6.3.8 Another project, " Improved Methods of Characterizing and fl Modeling Contaminant Transport around High-Level Radioactive Waste Sites,"
will examine issues which include the effect of measurement length scale
?
on permeabilities measured from cross hole hydraulic tests, the feasi-i j
bility of heat tracer experiments, the modeling of non-Fickian transport,
{
uncertainties in transport modeling due to uncertainties in measuring or j
predicting groundwater velocity, and the use of integrated sets of f
hydraulic and chemical data for calibrating models using parameter l
estimation by inverse methods. This will aid in the regulatory assessment of model validity.
i 6.3.9 Laboratory experiments done in the NRC HLW research project,
" Site Geochemistry," consider mineral surface /radionuclide ion inter-I j
actions, assessment of the thermodynamic data base needed for phenomeno-j l
logical modeling of retardation, hydrothermal rock / water interactions, and redox controls and buffers far from the emplaced HLW. All of these aspects of geochemical retardation are important to radionuclide transport l
but they are not explicitly reflected in current modeling practices tha'.
1 l
x-
use laboratory-measured solid / aqueous concentration ratios and retardation factors instead of treating geochemical effects mechanistically.
In another geochemistry project, " Valence Effects on Adsorption," at the Oak Ridge National Laboratory, the solubilities of various radionuclides species and the validity of using single values of electrochemical potentials to characterize the geochemistry of whole sites are being examined. Solubilities of species and speciation of radionuclides in general are not reflected in the current simple retardation models. Other research in this project has highlighted the ambiguity in the usage of electrochemical potentials in geochemistry and has raised serious doubts j
about the use of the concept in HLW applications. This research will aid in establishing a regulatory policy regarding these issues.
6.3.10 In the area of flow and transport in unsaturated media, the major HLW research project is " Unsaturated Flow and transport through Fractured Rock Related to HLW Repositories" being conducted at the University of Arizona. This work is designed to test basic hydrogeologic and geochemical assumptions used in DOE's site characterization and per-formance assessment studies at the Yucca Mountain site.
In order to test 1
these assumptions and to verify and validate both the field characteri-zation methods and unsaturated flow and transport models, a field i
experimental site near Superior, Arizona is being developed. Specfally
~
designed inclined boreholes and downhole hydraulic testing methods both for air and water flow properties are being used to develop a real-time and site specific data base for use in matrix-fracture models. The collected cores are being analyzed in the laboratory for both flow and chemical properties for use in testing coupled frac ure-matrix flow and transport models. Chemical sampling techniques are being developed for collecting unsaturated zone vapor and liquid samples, which will be used to analyze hydrochemical facies and environmental isotope movement.
Fracture characteristics such as effective aperatures, orientations, and continuity are being obtained and will serve as input to the previously developed three-dimensional fracture generator model. Both discrete fracture models and porous equivalency models will be used to simulate unsaturated zone conditions at the Apache Leap Tuff site using the 29
1 collected data for determining if DOE's methods, models, and their inherent assumptions are correct.
6.3.11 The " Laboratory Studies of Thermoconvective Phenomena in High-Level Waste Disposal and Development of Empirical Heat Transfer Correla-tions for Repository Licensing," consists of experiments on thermohydrologic phenomena applying the principle of similarity. The experiments are designed so that the thermohydrologic system in the laboratory is characterized by dimensionless numbers that apply equally to full scale repositories The final results of the experiments are expected
'g to provide some information on the degree of resolution of geologic systems which is needed for adequate predictions of repository-related phenomena close in to the waste emplacement areas.
6.3.12 The NRC HLW research program also has a set of projects that consider both natural systems and laboratory experiments to indicate and test the adequacy of models of the performance of the engineered barrier system. The engineered barrier system consists of manufactured waste packages, packing materials around canufactured waste packages, and backfills in repository tunnels. Some of the projects mentioned above in connection with the natural barrier system also consider aspects of the engineered barrier system.
In several of the projects on the engineered barrier system, consideration has had to be given to the interaction between the part of the engineered barrier system being considered and the surrounding natural environment.
6.4 Earth Science /Seismotechtonic Research Appended to this Program Plan is a " Proposed Earth Science Seismotectonic Research Program Plan for the Siting of an HLW Repository."
This Plan defined the earth science research issues necessary to support licensing positions and actions in the siting and design of geologic repositories for the disposal of high-level radioactive waste. The neotectonics, and engineering geology.
It. addresses issues about which there is considerable uncertainty and for which the NRC requires guidance 30
in establishing investigation needs and design criteria. The issues addressed are basically generic issues or of regional significance which are considered appropriate areas of responsibility of the Office of Nuclear Regulatory Research.
Certain of the needed research projects contained in the plan are clearly the responsibility of the DOE to carry forward in preparation for submittal of their application for a license to construct a repository.
Examples would be those earth science and seismotectonic investigations l[
designed to reduce uncertainties in site characterization of specific sites, such as experiments that would instrument rock' bodies similar to those of candidate sites.
Investigations that would model the response of particular repository designs to vibratory ground motions would also be the responsibility of the 00E.
Other projects are appropriate for regulatory research, such as the suggested study to detennine whether or not high frequency attenuation relationships and effects on wave fonn for high attenuation values can be extrapolated to regions of low attenuation. Also, study of the alteration of ground water flow by seismic event is of interest to the NRC to understand the importance of these events to both HLW and LLW waste disposal.
OtherinvestigationsareofinteresttoboththeDOEandNRC,butthe responsibility for carrying them out is not so clear. Ongoing discussions between the staff of both organizations will clarify jurisdiction and assign priorities.
\\
Research to implement this Plan will begin with a single modest project in FY88, and accelerate as funds become available.
31
7.0 OTHER RESEARCH AREAS There are a great number of other subject areas where research could profitably be done. Many of them fall legitimately within the NRC'S area of regulatory concern.
Examples are in the interface of Nuclear waste facilities with the environs such as socioeconomic impacts, land use planning for long time periods, and historic and archeologic ispacts.
Such research is not now planned due to the limitation of research funds and the lower priority compared to items with direct health and safety significance that such research must be given.
(
1 1
1 32
~
- 8. 0 COORDINATION WITH FOREIGN INTERNATIONAL WASTE MANAGEMENT RESEARCH PROGRAMS An integral part of the NRC research program is participation in various inter-national activities through its staff and contractors. The NRC objective of the participation is to take advantage of foreign research results for NRC application.
In exchange, results of NRC research relevant to other nations' programs is provided by NRC. general, international cooperation is achieved in two ways:
(1) Formal Cooperative Agreements and (2) Participation by NRC staff and contractors in symposia, working group meetings, and workshops. Currently, the NRC has established formal Agreements with CEA (France), JAERI (Japan), and NAGRA (Switzerland) through which information is exchanged and site visits are conducted. Fomal agreements with Canada and Great Britain are also being negotiated.
Under the Agreement with JAPAN, the JAERI is currently conducting experiments related to HLW glass leaching (dynamic leach experiment), HLW container de-gradation (slow strain rate test of carbon steel), and LLW radionuclide migration.
Under the NAGRA Agreement, the Swiss are currently conducting experiments concerning the following:
1.
Hydrologic tests (frac +.ure flow and heat effects on flow characteristics) in crystalline rock at the Grimsel site and in northern Switzerland, 2.
Performance tests of waste package / backfill / host rock interactions to obtain radionuclide source term data, and 3.
In situ measurements of radionuclide migration in crystalline rock to investigate the relationship between radionuclide migration rate and ground water flow rate.
Under the Agreement with France, CEA is conducting studies in the following areas:
33
1.
Waste form characterization tests and experiments related to understanding of the characteristics and long-term performance of conditioned high-level waste and transuranic waste.
(Information from the Vitrification Facility at Marcoule, France is being utilized),
?.
Studies concerning methods and data for evaluating radionuclide migration from the repository to the biosphere utilizing radionuclide migration models that include hydrological and geochemical considerations and results from integrated radionuclide experiments.
3.
Studies concerning methods of classifying, treating and disposing of low-level radioactive waste, which utilize French experience at low-level waste disposal facilities related to waste isolation perfomance and the results of waste form characterization tests and experiments, to establish the technical bases for the "de minimus" issue for low level waste and establish limits for alpha radionuclides in shallow land burial, and, 4.
Studies concerning methods to be used for analyzing and assessing operational safety at waste disposal sites.
NRC staff and contractors are participating in such international programs as HYDROCOIN, ISIRS (International Sorption Infomation Retrieval System), and INTRAVAL, as well as participating in a number of IAEA working groups.
J NRC is also working jointly with AAEC (Australia) to study natural analogs to HLW migration.
34
APPENDIX TO PADI0 ACTIVE WASTE MANAGEMENT RESEARCH PROGRAM PLAN EARTH SCIENCE SEISM 0 TECTONIC RESEARCH PROGRAM FOR THE SITING 0F A HIGH LEVEL RADI0 ACTIVE WASTE REPOSITORY Purpose and Scope:
The purpose of this document is to define the earth science research issues necessary to support licensing positions and actions in the siting and design of geologic repositories for the disposal of high-level radioactive waste. The focus of the document is on tectonics and related sub-fields of seismology, neotectonics, and engineering geology.
It addresses issues about which there is considerable uncertainty and for which the NRC requires guidance in estab-lishing investigation needs and design criteria. The issues addressed here are basically generic issues or of regional significance which are considered appropriate areas of responsibility of the Office of Nuclear Regulatory Research.
Regulatory Research Role:
The licensing role of NRC in the siting, construction and operation of a high level radioactive waste disposal repository is to make informed judgment en the adequacy of the license application and to verify that the repository will meet the performance requirements in 10 CFR Part 60 and the EPA standard in 40 CFR Part 191.
Some of the criteria of 10 CFR Part 60 are essentially the same as for conventional civil structures.
In those cases informed licensing judgment can be based on the present engineering and scientific state of practice.
However, other criteria and performance objectives are unique to geologic repositories because of (1) the goal of isolation of radionuclides from the accessible environment as defired in 10 CFR 60, (2) the 10,000-year requirement for the isolation within the underground storage facility, allowing for only slow releases during most of that period, and (3) the expected high thennal stress in the in-situ rock.
In those cases informed licensing judgment requires decisions based on considerably greater uncertainties in predicting long term stability than have been heretofore required.
It is the role of 35
research to investigate methods and obtain information not currently available that will reduce uncertainty in the repository licensing effort.
The following discussion provides suggestions for research topics considered likely to reduce uncertainty and to enhance NRC's efforts to provide guidance and informed judgement in the licensing of a high-level radioactive waste repository.
I.
TECTONICS The plate tectonics model has provided an understanding of linear and arcuate earthquake belts as plate boundaries where stored strain is released because of the movement of plates with respect to each other.
It has, however, been less instructive with respect to the causes of intraplate seismicity.
It is generally assumed that stresses at the plate margins are transmitted to plate interiors and are at least in part responsible for the elastic strains that result in sudden releases as earthquakes.
It is also assumed that because the transmission of stresses over great distances must be slow, the rate of strain build-up is also very slow.
Futhermore, unlike the narrow zones of seismicity associated with plate boundaries, intraplate seismicity is more diffuse and less subject to prediction. Strain releases in continental plate interiors may occur at great depths on unknown structures, or near the surface on pre-existing structures fortuitously oriented with respect to stress direc-tions, or on structures formed within the contemporary stress regime.
Intraplate seismicity may be of such low magnitudes that it is only detectable by sensitive instruments, as "microseismicity," or violently destructive like the New Madrid 1811-12 events or the Charleston, SC, 1886 event.
Despite the diffuse character of continental /intraplate seismicity, and the low rates of deformation, concentrated research efforts in geophysics, geology, and neotectonics, much of it sponsored by the NRC, have delineated several active seismic zores, determined the limiting seismic substructures and/or the probable return periods for events such as the New Madrid and Charleston earthquakes, using deterministic evidence developed during those investigations.
36
To address these critical issues and to develop an independent data base for evaluating the information and interpretations to be included in the site char-acterization reports and the final safety analysis reports, the following re-search prograns in the related subfields of Seismology, Neotectonics and Engineering are recommended.
II. SEISMOLOGY A.
SEISMOLOGY RESEARCH ISSUES The siting, design and construction of a geologic repository will require that several new seismological judgments be made, because (1) The length of time that the underground structure is required to perform is so long that the site will likely experience ground shak-ing in excess of that experienced in the region in historical times.
(2) Underground structures have never been designed to meet as many per-formance objectives as are required of a radioactive waste repository. These objectives include not only structural stability but also the integrity of the canisters, the integrity of borehole and shaft seals, and the integrity of the rcck mass as a part of the isolation system.
(3) The long-term isolation of the repository depends critically on control of groundwater flow. Modification of flow-paths due to a major seismic event is of concern in evaluating performance objec-tives and potential release rates.
One of the areas with significant levels of uncertairty is seismic wave propa-gation at depth, because of the lack of data and related analytical techniques.
Included under that broad topic are: ground motion variations arising from changes in propagation across geological discontinuities; frequency and strain level dependence of seismic wave propagation; and the relationship between seismic / tectonic forces and ground water flow.
37
b k
i 1.
Uncertainty in Ground Motion There are few data on seismic ground motion at repository depths. Even for surface facilities the data base on strong ground motion is far from complete.
During the last several decades there has been considerable information gathered and models developed on the relationship of surface ground motion to magnitude and distance. However, very limited data is available with respect to subsurface facilities. Much of the data base on subsurface ground motion is summarized in a Lawrence Livermore National Laboratory document, UCID-20505,
" Effects of Earthquakes on Underground Facilities; Literature Review and Discussion" by D. W. Carpenter and D. H. Chung.
In general, ground motion at depths of a few thousand feet, both accelerations and displacements, are thought to be less than those at the surface. How much attenuation occurs is variable, however, and seems to depend strongly on site conditions. The work of Ralph J. Archuleta, conducted in part for NRC, shows that a particular source parameter, the corner frequencies, of subsurface and surface recorded ground motions is nearly the same for a particular experimental configuration over a depth interval of about 160 m.
He noted that recorded motions at the surface are more complex than those at depth and much of that complexity is due to surficial conditions. These observations, however, involve relatively shallow depths and the transmission of ground motions through soil, not bedrock, i
l There is little data on attenuation relations at depth since deep underground structures are rarely instrumented to measure vibratory ground motion associated with earthquakes, In summary, little is known about subsurface accelerations in absolute terms, and as compared with surface accelerations. Data that exist indicate subsurface motions in general are less than surface motions but the amount of difference between them depends on the surface conditions for any specific locale. This is not surprising in that individual site conditions have been known for some time to be a major factor in detennining the character of ground 7
motion at a site. Although there is no direct test of the problem, all studies suggest that the difference between subsurface and surface strong ground 38
notions at a "hard rock site" should be considerably less than for a " soft soil site". A significant part of the major problem is a lack of data.
2.
Unceyta,intLjp,,Re,s,ponse of tindernround Structures to Earth:;utkes 1
The response of underground structures to a seismic event is a concern overlap-ping the disciplines of seismology and engineering. The seismologist is interested in predicting the size of the earthquake likely to affect the site, the resultant level of ground motion at depth to which the repository may be subjected, and the spectral properties of the seismic waves. The engineer, however, is concerned with predicting the response of the underground structure to the forces generated by seismic events that act upon the structure and to provide state-of-the-art techniques to mitigate adverse effects. Although engineering issues are addressed under another heading, it is important to recognize that uncertainties in seismology in the areas of subsurface ground motions, accelerations and frequencies, lead to further uncertainties in engineering predictions of seismic response of the structure. More seis-mological information is needed to prevent such compounded uncertainties in the licensing process.
B.
RESEARCH TO ADDRESS SEISMIC UNCERTAINTIES 1.
The lack of data concerning ground motions at depth contributes a large part of the uncertainty related to seismic issues in repository performance. Therefore, a program should be instituted to increase the underground strong motion data base by placing seismometers in deep (1000'-3000') boreholes or mines with known geometries in active seismic areas.
An array of instruments would be preferable so that attenuation relations could be established. Where possible, the seismometers should be installed in regions where HLW repositories are proposed within rocks that are similar to the rocks selected for HLW repositories and at the same depths.
2.
Data concerning the differences and similarities of seismic response at depth and at the surface may be obtained with a comparative study of surface and subsurface seismic effects and wave characteristics in (1) bedrock surface 39
)
vs. bedrock subsurface, and (2) deep soil surface vs. bedrock subsurface.
Comparisons should be made of:
a.
Variation of ground motion amplitudes b.
Wave form and frequency content
{
c.
Attenuation relationships: Can high frecuency attenuation relation-ships and effects on wave form for high attenuation rates'be extra-polated to regions of low attenuation--or are they entirely different? In other words, is extrapolation valid whether or not i
attenuation is vertical or horizontal?
d.
Contribution of peak particle velocity vs. peak acceleration to near-field damage.
l Where possible, bedrock types should be those of the candidate sites: welded j;
tuff, basalt, granite bodies, salt domes and beds.
3.
An LLNL report on the effects of earthquakes on underground facil-ities observed that small near-field earthquakes required further investigation i
because experimental, analytical and blast data indicate that 4
(1) Small near-field earthquakes generated high frequency waves that damaged model underground openings which were otherwise stable when larger more distance event records were used; l
(2) for the same level of ground motion, nearby small earthquakes are more l
I likely to cause damage than larger, more distant earthquakes because the ground motion from small events is more impulsive, inducing higher stress.
1
-l (3) With respect to small earthquakes, there appears to be a closer j
relationship between peak velocity and underground damage than between
-)
i acceleration and damage.
i With these observations and the small amount of data available concerning small earthquakes, it is recommended that a study of the relationship between peak l
velocities and source parameters be undertaken to determine if it is true that, i
I l
40 l
according to the LLNL report, a small fault in the near-field to a nuclear waste repository could have seismic significance disproportionate to its size.
Such a study should attempt to:
j Relate such parameters to regional stresses and type of faulting; a.
b.
Determine near-field effects on subsurface rock openings such as tunnels and shafts; l
c.
Compare with data for large earthquakes; and d.
Evaluate the significance of results of the investigation with respect to repository performance objectives, and to preclosure structures, systems and components important to safety.
j 4.
The relationship of altered ground-water flow and earthquakes is poorly understood. Hydrologic changes in response to a seismic event were recorded in the San Francisco earthquake of 1906, and studied in more detail in-connection with the 1985 Borah Peak, Idaho, earthquake. Significant increases in discharge, out to 90 Km beyond the rupture surface, in streams, wells, and springs, and elevation of water tables by up to 4 meters within the epicentral region suggest a need to learn more about the mechanism and geo-hydrologic relationships. Such observations indicate a close relationship between seismic events and groundwater behavior. As ground-water adjustments to earthquakes have serious implications for the isolation of subsurface geologic repositories, it is advisable that an investigative program of the relationship between earthquakes and ground-water flow be undertaken. Such a program should:
a.
Develop a world-wide data base on ground-water flow path modifications and adjustments in response to fault movement and/or a seismic event.
Information should include geologic and tectonic setting, seismic history and details of seismic events, and/or surface fault movements involving ground-water response, pre-event ground-water data (aquifer character and depth, flow rates and 41
conduits), and changes of any of these, duration of flow path and
{
rate modifications, variations in response for different events in same locality, any other relevant information.
I b.
Develop predictive m'cis for ground-water response to seismic events with respect to seismic character and geologic / tectonic settings-based on evaluation of data base. Emphasis should be on characteristics of candidate repository geologic / seismic settings.
III. NE0 TECTONICS 1
A.
NE0 TECTONIC RESEARCH ISSUES In evaluating candidate sites for a high level radioactive waste repository in bedrock, regional tectonic strains, surface and subsurface structures, and the likely resulting seismic occurrences in the region close to the sites are j
necessary considerations for determining seismogenic structures and the design basis maximum magnitude events.
Repository perfonnance, bedrock integrity, modifications of hydraulic conductivity and potential resultant radionuclide releases depend in large part on the contemporary tectonic setting. The more that is known or understood of the tectonic environment, stress orientations.
i l
strain rates, and active structures, the fewer uncertainties are introduced into the scenarios that will be used to demonstrate the suitability of l
candidate sites in meeting the technical criteria specified in 10 CFR Part 60.
i As much of the data will be subject to interpretation, independent assessment of the seismotectonic information will reduce uncertainty and provide confidence in licensing positions relative to repository performance assessments.
[
B.
NE0 TECTONICS RESEARCH C0tWON TO ALL SITES Because the tectonic framework is specific for each geologic setting, neotec-tonic investigations are necessarily site-related. The types of investigations and kinds of information sought are similar, although the nature of the l
geologic setting and rock types, proximity to other regions, the age, and the 42
amount of infonnation already available will dictate the variations in the investigative program and the specific approach.
Although site investigations are the responsibility of DOE, independent studies by the NRC are Iniportant to form the basis by which NRC reviewers can assess the investigations and analyses performed by DOE.
In general, the types of inforwation to be included in a tectonic investigation i
l for all candidate sites are -
1 1.
Mapping of all regional and local structures within the site region, determination of age of latest movement, and sense of displacement; l
2.
Determination of the relationship of macro-and microseismicity i
to mapped structures, gravity and magnetic anomalies in the site region; j
3.
Direction and magnitude of principal regional stresses; rela-tienship to mapped structures and displacements; f
I 4
Strain rates and relationship of these to seismic recurrence i
intervals; 1
5.
Changes in strain rates based on historical and instrumental seismic data, geodetic changes, and structural history; 6.
Investigation of individual surface structures that indicate recency of movement and a potential for generating earthquakes or surface displacement. Data requirements include -
t i
a.
Sense, amount, and age of last displacement; h.
History of displacements; c.
Lengthoffaultandofsegmentofrecentmovement(s);and d.
Strike, dip and area of fault surface; i
43
. -- -. - 1
a 7.
Relationship of surface lineaments and geophysical anomalies to tectonic structures; i
8.
Establishment of an updated earthquake catalogue of the region; and i
9.
Development of a tectonic model or models to explain all the observations and relationships of 1 through 8.
i Investigations outlining details of more site related studies will be found in j
the following sections.
I C.
TECTONICS RESEARCH RELATED TO REPOSITORIES LOCATED IN BEDDED BASALT TheBasaltWasteIsolationProject(BWIP)isassessingthefeasibilityofa geologic repository in the Pasco Basin, which is founded on basalt, a dense and massive rock. Basalt is, however, a brittle rock of low ductility under a wide range of pressure and temperature conditions. The basalt, hundreds of meters
)
thick, has been deforwed by folding and faulting by north-south compression j
duringtheTertiaryPeriod(65-2millionyearsbeforethepresent(MYBP)).
Jointing and shear fracturing are comon in exposures of the basalt around the Pasco Basin, resulting from the deformation.
i
)
The reference repository site in the Pasco Basin is in the core of a syncline.
the Cold Creek syncline, in the basalt. The syncline is buried beneath sedimentary deposits, so much of its character is not observed.
Inasmuch as i
the isolation of the repository is dependent upon the integrity of the bedrock barrier in large part, a study of the subsurface characteristics of a syncline l
in basalt may increase confidence in the likelihood of a repository in such a l
structure to meet the performance objectives of 10 CFR 60.
In addition, other uncertainties concerning structural characteristics of basalt are addressed in the following suggestions:
1.
Cold Creek Syncline. Hanford, Washington.
44
~.
Study the relationship between fracturing and folding of syn-a.
clines by studying surface analogues to the Cold Creek Syncline, such as the Vantage Syncline, several miles north of the Hanford tite, to clarify the following issues -
(1) is fracturing more intense along fold axes than'within the flanks; I
6 (2) what are relative contributions of stress directions and fold geometry to fracture development and orientation; i
(3) is residual stress more intense in synclinal hinges than on i
limbs; and 1
)
(4) do residual stress orientations depend on position in the j
syncline or on regional stresses?
i b.
Using worldwide data, determine whether or not there is a relationship between synclinical axes and seismicity, i
2.
Ambiguities relating to the structure make it uncertain whether the j
many faults in the basalt in the Hanford Region project downward to the base of the basalt, flatten off at some depth, or die out at shallow depths. Theories j
vary as to the significance and/or extent of faulting. One view interprets the faults as shallow, discontinuous secondary effects of the primary folding of brittle rock, that die out within the folds. Another interpretation views the folds as secondary effects of large scale, low angle thrust faulting, which j
flatten off at depth. The uncertainties concerning the possible steep projec-l tion of faults to depths where earthquakes occur, or the flattening of faults that may then pass through or under the reference repository may be reduced by investigations to detemine the character of the faults in the fold belt.
An investigative program therefore is recommended to detemine the relationship l
between folds and faults in the Yakima Fold Belt, just west of the Pasco Basin.
l the mechanisms and tectonic causes of the defomation. Are faults primary, deep seated fractures, or do they flatten with depth and may therefore pass I'
45 i
~ _, - _. - _ _., _
_ _ _ _ _.,. _ _, _ _. _. ~.
i through or under the reference repository?
Is there evidence for the decoupl-ing of the basalt and underlying bedrock during deformation?
l 3.
The nature and structure of the rocks below the basalt have not been 2
determined from data, but by extrapolation, because the dense basalt has not I
allowed any geophysical penetration to the rocks below. There is a very large gap in our knowledge between the surface and sub-basalt geologic character.
Since earthquakes originate in the deeper crust, it would be important to know l
if any structures capable of localizing earthquakes are present, and if these have propagated upward into the basalt. Up to now only oil company drilling programs have provided direct information, but the data have not yet been made available to the public. This infomation will reduce uncertainties concerning the sub-basalt potential for seismic activity and for surface structures to be I
upward propagations of sub-basalt features, in the vicinity of the BWIP repository.
y 4
j A research program, therefore, is suggested to define the nature of the tectonic structure in rocks below the Columbia River Basalts. Detemine i
whether or not structures within the basalt reflect structures in the rocks l
below it. Source of data includes oil company drilling and magnotelluric exploratory results.
I D.
TECTONICS RESEARCH RELATED TO TPE WELDED TUFF REPOSITORY AT NEVADA TEST j
SITE
}
j 1.
Geological, geophysical, and geodetic investigations indicate that j
the Sierra Nevada west of the Nevada site are rising and rotating about an l
approximately N-S horizontal axis. The effects of this tectonic activity on j
the tectonics and seismicity of the Basin and Range Province in general, and on j
the Yucca flat region in particular, should be assessed. This should be done
}
through analysis of the published information and any other seismic, tectonic and/or geodetic data, i
l 2.
Establish a data base from world-wide data to increase the accuracy l
of predicting fault attitudes at depth in welded tuff from surface and i
near-surface deformation.
Information should include:
i
}
46
a.
Regional geologic setting b.
Contemporary stress orientations c.
Fault and joint crientations, characteristics, and variations d.
Thickness and shape of the tuff body e.
Boundary conditions of the tuff body f.
Nature of bounding rock bodies, structures, and orientation Compare NTS regional and local data for the same features to determine if there is a consistent pattern that reduces uncertainty in prediction of structural characteristics.
3.
Recent investigations suggest the possibility that many of the Basin and Range faults flatten with depth and that the bedrock is currently sliding and rotating along some of the faults. Several faults in the Yucca Flat j
vicinity are extensions of Basin and Range faults and may have some of the same potential for flattening and sliding. Such faults may pass through or under the Yucca Flat Repository, and therefore present uncertainty concerning the stability of the site. An investigative program is suggested to determine the nature, attitude and recency of faulting in the NTS area, using already available information and investigative techniques necessary to detennine subsurface orientations and potential for sliding.
4 Determine the potential for renewed volcanic activity in the Nevada Test Site region.
Evaluate the potential effects on a repository in tuff of j
possible volcanic hazards such as magma rise, renewed hydrothemal activity, or I
high heat flow from depth.
E.
TECTONICS RESEARCH RELATED TO THE BEDDED SALT REPOSITORIES 1.
Several faults that offset Cenozoic sediments have been mapped adjacent to Deaf Smith County in western Texas.
It is reconnended th6t an investigation be undertaken of the Cenozoic mapped faults in Potter and Oldham Counties, some of which may extend into Deaf Smith County, to detemine the extent and age of those faults that may impact on the Deaf Smith site.
Included should be an evaluation of the seismic potential, evidence for l
paleoseismic activity, and whether these may influence pathways of dissolution, 47
and/or trigger earthquakes. Some faults in nearby New Mexico, documented an Cenozoic, such as the Alamosa Fault and the Bor.ita Fault, should be studied in this manner to determine their seismic potential.
2.
At least one west-northwest striking fault of the Wichita Frontal Fault system of southern Oklahoma, the Meers Fault, has experienced substantial displacement within the past several thousand years, but is not characterized by seismicity. Although this system of f aults apparently passes north of the Palo Duro Basin, a similar west-northwest structural grain (basement faults and joints) is predominant within the basin. Numerous Landsat lineaments have been identified across the basin with a west-northwest trend. Many of these linea-ments are caused by linear scarps, alignments of playa lake depressions, and linear stream segments, a.
Investigate the west-northwest striking linear features in the Palo Duro Basin and adjacent areas to determine if (1) they are controlled by tectonic structures, (2) there is a relationship between these and the Wichita Fault System, and (3) there is any evidence that they may have experienced recent movement. The significance of the results for a proposed depository in nearby salt beds should be assessed.
b.
Study the seismicity and tectonics of the Amarillo-Wichita Uplift, and associated faults adjacent to the Palo Duro Basin. Evaluate the potential of this tectonic region to affect the integrity of the pro-posed salt site in west Texas.
- 3. -
Specific research is needed with respect to bedded salt repositories to improve the extent to which the characteristics of geological features such as structures or stratigraphy, as determined by mapping at the surface, can be extrapolated to the depths of a proposed HLW repository. Geologic structures are mapped at the surface in these regions and it is not clear what the 40
characteristics-of those structures are as they penetrate downward into the layered evaporites and sediments (i.e., do they flatten into bedding, ramp down, or continue at the same attitude?).
Conversely, there are structures identified by geophysical techniques in basement rock beneath the basins.
It is not known whether or not they propagate upward through the strata in the
(
basin or what their character is if they do. Research is needed in methods to identify and define such structures in bedded salt and to determine their significance to the repositories.
IV. ENGINEERING GE0 LOGY / ROCK MECHANICS A.
ENGINEERING / ROCK MECHANICS RESEARCH ISSVES
\\
Engineering issues related to a deep geological repository are concerned with I
two major considerations:
i (1) The overall bulk rock properties, such as density, porosity and per-meability, fracture patterns, fracture density, etc.
1 i
(2) The response of the repository to seismic ground motion, which j
depends not only on the mechanical properties of the rock, but on the j
geometry of the repository such as the cross-sectional shape and interconnected tunnels, and on the seismic wave characteristics, such t
J as frequency and peak velocity.
i i
l The role of bulk rock properties and seismic parameters needs to be understood in assessing the behavior of different rock materials, backfills and seals undervaryingstatic(insitu), dynamic (seismic),andthermalstresses. This l
information is needed in predicting the likelihood, nature and extent of damage I
to underground openings in response to seismic stresses. Such damage can j
affect the hydraulic conductivity of the repository rock medium, the stability of the openings, rock integrity, and pre-existing planar discontinuities such as faults and,ioints.
j Large uncertainties exist with respect no these issues because the state of the art has not yet provided the necessary technologies for analyzing the i
49
three-dimensional response of subsurface openings to seismic ground motion in complex or inhomogeneous rock bodies. Nor have engineering studies developed numerical methods for assessing, in three-dimensional space, the behavior of openings in rock in response to dynamic stresses.
As licensing judgments, therefore, must be made relating to the long period of performance and the extreme environmental conditions, research to identify methods of dealing with and reducing uncertainty in estimating the site bulk rock properties and seismic response of underground openings are high priority items because they affect those judgments.
B.
RESEARCH TO ADDRESS ROCK MASS UNCERTAINTIES The engineering properties of a rock mass are to a large extent determined by the distribution of inhomogeneities, which may be grain size, composition, porosity, fractures and other discontinuities within the rock mass. The distribution and orientation of fractures is extremely important in determining the strength and hydraulic properties of a rock mass.
Even after the repository is completely excavated, there will be an unreducible uncertainty about the engineering properties in the unexcavated rock around and within the repository. That unexcavated rock will be important for the perfor-mance of the repository as its behavior will affect the response of the under-ground structure. Also, it is important for the isolation of the waste as it is part of the pathway to the accessible environment.
It is desirable, therefore, to establish the uncertainties in estimating the engineering properties or variability of bulk rock mass in the unexcavated part of the repository rock body. These uncertainties can be estimated by a critical statistical evaluation of case histories of underground construction projects.
There are two well developed data bases for this study, the civil engineering community and the mining industry.
In both of these, where underground struc.
tures are proposed, pre-excavation deterministic and geostatistical site char-acterization provides for prediction of underground site conditions and the 50
information base for the design of the structure. Subsequent excavation may uncover new information about the site that will require design modification.
i Mining and civil engineering records kept of "as predicted" and "as discovered" data can provide a data base for statictical evaluation of the success or variations between the prediction of site conditions based on the j
pre-excavation site characterfration and the observed conditions following excavation. This could provida the empirical data base on which to evaluate uncertainties in subsurface site character 12ation, i
A strong effort should be made to tap the data base within the regions in which HLW repositories are proposed; and a similar effort should be made, worldwide if necessary, to obtain data from large volumes of rock similar to those within which an HLW repository is planned.
C.
RESEARCH TO ADDRESS SE!SMIC STRESSES AND THE EFFECTS UPON UNDERGROUND EXCAVATIONS in general, underground structures apparently experience less damage in an l
earthquake than surface facilities. This is in part due to the expected reduc-tion in ground motion with depth. However, it is in part due to what appears j
to be an inherent robustness of underground structures with respect to ground motions. Data concerning this issue is also sumarized in 0C10-20505. There is a reasonably good qualitative data base on underground structure response to l
earthquakes. Dowding's work on the subject is reviewed in the above document.
From his review of 71 tunnels subjected to earthquakes he concluded the follow-ing:
(1) for surface acceleration less than 0.199, no damage has been noted to underground structures; (2) for acceleration of 0.19g to 0.4, minor damage is 9
reported; (3) major damage can occur at levels of acceleration in excess of O 4g; (4) collapse is observed only at levels of acceleration above 0.50 There are a number of complicating factors, however. Damage to underground structures is greater in areas where shafts and portals intersect because of high stress concentrations.
In addition, the frequencies of motion that cause j
damage to underground structures are different from those that cause damage to surface structures. Also, there are indications that the damage that occurs for a given level of ground shaking is a strong function of the cuality of the 51
rock, i.e., the nature and density of joints, fractures or other discontinuities.
The consequence of this uncertainty is that the overall response of the waste facility to ground shaking is not well known. Thus, there is significant uncertainty related to the response of the repository to a design basis event.
The character of the response is of concern primarily in the preclosure period because of surface operations and the requirement for retrievability,'00th of which may be compromised if damage results from a seismic event.
The deformation of underground structures such as tunnels in response to l
seismic motion is of three types: axial, curvature, and hoop. Axial and curvature defomations result when seismic waves propagate parallel with or oblique to the tunnel. Axial deformation involves alternating regions of compressive and tensile strain in the rock along the tunnel axis. Curvature deformation creates a sinusoidal curvature of the tunnel. Hoop deformation refers to the change of cross-sectional shape of the tunnel when the wave travels normal (perpendicular 1 or near normal to the tunnel axis. For these f
types of deformation, there are two-dimensional analytical methods to analyze i
static and seismic stresses and stress concentrations in honogeneous rock.
However, analytical methods in inhomogeneous rock and in three dimensions are extremely difficult so that there are only some simplified techniques for dealing with these.
In order to determine the strength of the rock, the level of stress concentra-tion, and the level of ground motion the tunnel can withstand, it is necessary I
to evaluate the applicability of current analytical and numerical modeling methods to the real rock situation.
To identify the uncertainties inherent in the present state of the art tech-niques the following studies are recommended:
1.
Identify and test methods for the 3 dimensional analytical, and numerical modeling of the seismic response of an opening in rock such as a tunnel or shaft.
1 52
1 (a) Evaluate the applicability of current simplified 2-dimensional models in homogenous media to 3-dimensional structures in inhomogeneous media. Determine the limits and uncertainties inherent in the simplifications of the real rock conditions.
(b)
Identify and test 3-dimensional analytical solutions for seismic design and support requirements for openings in rock, such as tunnels and shafts using properties of a variety of rock types such as those proposed for repositories.
1 (c)
Identify methods using 3-dimensional models, for the numerical evaluation of seismic stresses on tunnel-shaped openings in rock due to axial and cross-sectional (curvature) deformations in a variety of rock types proposed for repositories. Computerized l
numerical modeling of static and dynamic behavior of underground structures are used to determine the stability of underground structures in response to in situ and earthquake stresses. Such models make possible the study of potential seismic damage such as new cracks or the enhancement of preexisting ones, ifp to now, primarily 2-dimensional models have been studied, although computer technology can pemit the more complex three-dimensional analysis.
i (d) Determine the effect of the complex geometry of underground i
facilities on their response to seismic loading. The number of l
interconnections and the total number of tunnels are likely to affect response. The effects of the direction of dynamic load-ing, whether parallel, perpendicular, or oblique, with respect i
to tunnel shape, orientation, and depth need to be considered.
i 2.
To enhance the experimental and theoretical data bases, an analysis is proposed of the existing data bases of (a) the effects of strong ground motion on underground structures that were developed by LLL during the nuclear devices testing program, and (b) of the seismic response of underground structures in high temperatures, high stress regimes such as exist in the deep South African and Indian gold mines.
53
{
3.
Identify and test engineering measures to overcome high thermal stress in combination with seismic ground motion, with particular attention to l
(a) shaft stability (b) retrievability.
i l
4 Determine the potential for induced seismicity, rock burst, and frac-l turing due to stress release within the site rock as a result of excavation for i
l a repositnry. Determine the time-dependence of these hazards for various l
repository rock types in varying stress and themal regimes. Test various measures to mitigate the hazards studied, i
5.
Identify and test preventive or remedial engineerinc measures to seal the potential damaged rock zone (DRZ) that may result from excavation activity.
Therequirementstosealexploratorypenetrations(e.g., shafts,boreholes)to keep them from becoming preferential pathways for water is stated specifically j
in 10 CFR 60 Section 134. A migration path closely associated with excavation
{
j procedures is the damaged or stress-relieved rock around such excavations.
If I
the DRZ develops during or after construction of a repository, it could become i
j the most direct flow path or high conductivity zone from the repository to the l
accessible environment or vice-versa. Furthermore, the existence of the DRZ has major implications with regard to retrieval, canister loading, etc. The most common mechanisms for the development of the DRZ around excavations such as shafts, tunnels, rooms, etc., include -
l a.
slip of rock blocks along pre existing discontinuities such as
.ioints t b.
rotation of rock blockst c.
development of nw fractures as a result of the excavation processt j
and j
d.
rock fracturing as a consequence of excess stress concentration.
Since the development of the DRZ during and after construction of the repository is likely, the impact of the DRZ on waste isolation perfomance and f
preventive nr remedial actions need to be addressed.
I D.
ENGINEEp!NG/ ROCK MECHANICS RESEARCH IN SALT SITES j
j 54 i
1.
Mechanical Behavior of Homogeneous Salt Rock: Major uncertainties continue to exist with regard to predicting the mechanical behavior of homo-geneous salt, especially at high temperatures.
Evidence to date suggests that I
there are substantial differences between predicted and measured borehole, shaft and room closures in salt. Salt creep uncertainties have serious impli-cations with regard to HLW disposal and retrieval in this medium.
Included in the impacts are -
a.
canister loading; l
b.
retrieval; c.
closures of emplacement rooms, access drifts, etc.; and l
d.
backfill compression.
2.
Effects of Impurities and Inhomogeneities in Salt. While the discus-sion above deals with pure salt (halite itself), major rock mechanics problems remain concerning the influence of inhomogenetties and nonunifomities in and arourd salt formations, e.g. fault:, breccias, brine and gas pockets, mud, i
shale, anhydrites, etc. Most tests to date have been performed on relatively pure salt. Research taking into account the impurities could provide more realistic insights into the behavior of in-situ salt formations. Other impor-tant topics that need to be looked into include -
a.
longtermperformance(uptoclosure)ofsaltreinforcement(bolts) especially due to effects of heat and brine migration; b.
brine migration considering the coupled thermal, mechanical, hydrologic and chemical effects; c.
compaction of salt backfill; arH d.
damaged zone and healing thereof around salt shafts, drifts, rooms, etc.
e.
problems associated with uncertainties concerning the influence of interbeds on in situ rock mass properties.
3.
Salt is one of the most water-soluble of natural geologic materials. Salt domes are commonly characterized by peripheral and internal weak zones that are 1'
created by the processes of solutioning and erosion of salt. The presence or absence of these weak zones is extremely important to the long-term integrity 55
l i
of the salt repository. The intrusion of groundwater into the dome is permitted by discontinuities such as faults, joints, karst or other permeable structures. Bedded salt shares this potential for such features. Research is recomended, therefore, to improve the state of knowledge in identifying and defining geologic and geomorphic features that have the potential of promoting dissolution, and in determining the relationship between those structures, their potential as hydrologic pathways, and salt dissolution zones, a.
Conduct research to establish whether or not there is a relationship between deep interior dissolution features, thinning of beds, base-ment faults, surface faults, lineaments, playas, regional joint systems or drainage features.
Identify measures to mitigate the effects of the presence of these features if a relationship exists.
b.
Institute a program to determine whether or not there is a relation-ship between dissolution of salt and karst features in carbonate rocks above and below potential repository host salt layers. Test measures to mitigate the effects of such relationships.
c.
Conduct research to evaluate the rates of dissolution of salt at the surface and at depth in the presence of faults and other pathways.
4.
In predicting the performance of a geologic repository, it is impor-tant to take into account the scale relationships between the structure and distribution of heterogeneities such as impurities, changes in composition, fractures, etc.
For testing to be relevant, the scale of the sample must be large enough, or sample selection random enough, to include a representative number of heterogeneities in the rock. Therefore, test the validity of apply-ing laboratory test results of core taken from salt domes or salt beds to the repository design in the rock mass, considering heterogeneities in the rock mass and other uncertainties. Assess how such laboratory tests reduce uncer-tainty, and characterize the remaining uncertainty.
5.
Establish a data base of the characteristics of faults located between salt domes and surrounding sedimentary rocks.
I 56
6.
Examine worldwide data on storage of equipment in mines in domes and salt beds to develop a data base for rock characteristics and impurities, room closures and retrievability, and to deterinine the viability of a geologic repository in salt.
7.
Perform research to improve the reliability of geophysical explora-l tory techniques that are used to identify inhomogeneities in bedded salt. The geophysical methods can be verified by other investigative techniques with greater resolution, but which cannot be used, or must be limited in the reposi-tory area, such as borings, test shafts, tunnels, etc. The features that con-I tribute to the inhomogeneity of the salt rock mass include:
thickening and
)
thinning of beds, clay interbeds or seams, muddy salt beds, joints and frac-j tures, brine / gas pockets, and inclusions. A data base of facts about the occurrence of such features in salt strata should be established from this research to provide a basis for more accurate predictions regarding the heterogeneity of salt repositories. Such heterogeneities impact on the j
predictability of the mechanical behavior of the salt.
4 1
l i
1 I
i i
1 57
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_earch programs in the areas of:
(a) materials and engineering, (b).
rology
.d geochemistry, and (c) compliance assessment and modeling. The pla 1so detal' the cooperative interactions with International waste management re arch program In addition, a proposed Earth Science Seismotectonic Research Program plan for adioactive waste facilities is appended.
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