ML19352E892
| ML19352E892 | |
| Person / Time | |
|---|---|
| Issue date: | 11/03/1994 |
| From: | Murphy A Office of Nuclear Regulatory Research |
| To: | Costantino C City Univ of New York |
| References | |
| NRC-2021-000179 NUDOCS 9411170061 | |
| Download: ML19352E892 (8) | |
Text
e November 3, 1994 Dr. Carl J. Costantino Department of Civil Engineering City University of New York New York. New York 10031
Dear Mr. Costantino:
Per Professor Gupta's request. I am sending you a copy of Paper I/3 entitled. " Status and Content of Seismic and Geologic Siting Criteria Revision.
10 CFR Part 100. Appendix A."
I estimate a 20 minute presentation with an additional 5 minutes for questions.
Sincerely.
Oriyr. ! !cned by
/In,v J..'iurphy Andrew J. Murphy. Chief Structural & Seismic Engineering Branch Division of Engineering Office of Nuclear Regulatory Research i
Enclosure:
As stated i
l Distrt>ution SSEB Reading File Central Files RES-2D-1 OFFC SSEBEES,
NAtAE AtAurphy l
DATE:
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Status and Content of Seismic & Geologic Siting Criteria Revision, l
10 CFR Part 100, Appendix A Andrew J. Murphy', Nilee.h C. Chokshi,
2 2
Roger M. Kenneally*, Rics. J B. McMullen Robert C. Rothman' and Phyllis A. Sobel'
SUMMARY
r In September of 1990, the Nuclear Regulatory Commission began the formal rulemaking process to revise the seismic and geologic siting criteria for l
nuclear power plants. In December of 1992 we reported to the Fourth Symposium on the philosophy and content of the proposed regulations and the draf t guidance documents as published for public comment in October and November of 1992, respectively.
Based upon the public comments and Commission guidance, the proposed regulation and draft regulatory guidance have been revised and are expected to be published in October and December of 1994, respectively.
This paper will describe the philosophy and content of the regulation and l
regulatory guidance.
l l
i BACKGROUND:
l On April 12, 1962, the Atomic Energy Commission (AEC) issued 10 CFR Part 100, l
" Reactor Site Criteria" (27 FR 3509).
On November 13, 1973, the AEC issued Appendix A to 10 CFR Part 100, " Seismic and Geologic Siting Criteria for Nuclear Power Plants," (38 FR 31279).
l A proposed rule to revise Part 100, Appendix A to Part 100, and sections of Part 50 was published for comment on October 20, 1992 (57 F_R 47802). The proposed rule change combined two separate initiatives dealing with non-
' Structural & Seismic Engineering Branch, Division of Engineering, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, j
Washington, DC 20555, USA
{
- Civil Engineering & Geosciences Branc5, Division of Engineering, Office of Nuclear Reactor Regulation, U.S. Nuclear Regulatory Commission, Washington, DC 20555, USA
' Low level Waste & Decommissioning Praiects Branch, Division of Waste Management, Office of Nuclear Material Sa tty & Safeguards, U.S. Nuclear Regulatory Commission, Washington, DC 20555, USA 1/3-1
=
_u seismic and seismic issues. The comment period, extended twice, expired on June 1, 1993.
Extensive comments, both domestic and international, were received.
The Commission was briefed on August 3, 1993, about the status of the proposed rule and the nature of the comments received.
In a Staff Requirements Memorandum (SRM) dated August 12, 1993, the Commission raised several concerns regarding the prescriptive aspects of the proposed revisions to Part 100 as well as its form and content.
In response the
.ff prepared an options paper, SECY-94-017, entitled, " Options with Regard to Revising 10 CFR Part 100, Reactor Site Criteria" and dated January 26, 1994, which recommended (1) that the non-seismic provisions of the proposed revision to 10 CFR Part 100 be i
withdrawn, (2) that Part 50 be revised to use updated source term and dose calculations for evaluating plant design, and (3) that Part 100 be revised to emphasize siting aspects by including basic site criteria, and (4) that the proposed revision of Part 100 regarding the seismic provisions be streamlined and be permitted to continue through the NRC regulatory review process for completing the rulemaking. In an SRM dated March 28, 1994, the Commission approved the staff recommendations; however, due to the substantive nature of f
the changes to be made to the rule the Commission stated that both parts were to be resubmitted for Commission review and reissued for public comment prior to the final rulemaking.
On July 27, 1994 the staff issued SECY-94-194 entitled, " Proposed revision to 10 CfR Part 100 and 10 CFR Part 50, and New Appendix S to 10 CFR Part 50."
This SECY paper contained the staff's proposed revision to the siting regulation as well as outlines of the regulatory guidance, (regulatory guides and Stanoard Review Plan sections, and sought Commission approval to publish i
the regulations for public comment and to prepare the regulatory guidance in accord with the outlines.
The Commission was briefed about SECY-94-194 on August 22, 1994.
In a revised SRM dated September 5,-1994, the Commission 1
approved publishing the proposed revisions of the siting regulation.
It is anticipat:d that they will be published about October 10, 1994 for a 120-day comment period and that the associated draft regulatory guid ce will te published about December 20, 1994.
The remainder of the paper will only treat the seismic aspects of the rukemaking.
SEISMIC ASPECTS OF THE PART 100 RULEMAKING i
Itikisophy and Content i
The proposed changes to the regulations and guidance documents reflect new information and research results and comments from the public on the first proposed revision of the regulations.
The proposed changes continue to reflect the philosophy that the regulation only contains the basic requirements and that the detailed guidance, which is contained in the current regulation, Appendix A to 10 CFR Part 100, be removed to guidance documents.
i Thus, the proposed regulation contains:(a) required definitions, (b) a i
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requirement to determine the geological, seismological, and engineering characteristics of the proposed site, and (c) a requirement to determine the l
Safe Shutdown Earthquake Ground Motion (SSE) and its uncertainty, to determine the potential for surface deformation, and to determine the design bases for seismically induced floods and water waves.
The guidance documents describe procedures acceptable to the NRC staff on how to carry out these required l
determinations.
The key alements of the approach to determire the SSE are presented in the following section and are described in the guidance documents.
Geologic and Seismic Siting The proposed regulation, Section 100.23 to Part 100, would identify and l
establish basic requirements. Detailed guidance, that is, procedures acceptable to the NRC staff for meeting the requirements, would be contained in Draft Regulatory Guide DG-1032, " Identification and Characterization of Seismic Sources and Determination of Safe Shutdown Earthquake Ground Motions."
NRC staff review guidelines will be provided in Draft Standard Review Plan (SRP) Section 2.5.2, " Vibratory Ground Motion," second proposed Revision 3, Two other SRP sections, 2.5.1, " Basic Geologic and Seismic Information," and
?
2.5.3, " Surface Faulting," will also be revised to assure consistency among the proposed rule, SRP Section 2.5.2, and dratt regulatory guide DG-1032.
The existing approach for determining an SSE for a nuclear reactor site, i
i embodied in Appendix A to 10 CFR Part 100, relies on a " deterministic" approach. Using this deterministic approach, an applicant develops a single set of earthquake sources, develops for each source a maximum earthquake to be used as the source of ground motion that can affect the site, locates the postulated earthquake according to prescribed rules, and then calculates ground motions at the site.
Although this approach has worked reasonably well for the past two decades, in the sense that SSEs for plants sited with this approach are judged to be i
suitably conservative, the approach has not explicitly recognized ancertainties in geoscience parameters.
Because of the uncertainty about i
earthquake phenomena (especially in the eastern United States), there have often been differences of opinion and differing interpretations among experts as to the characteristics of the seismic sources and the largest earthquakes to be considered and the ground-motion models to be used, thus often making the licensing process relatively cumbersome.
l Over the past decade, probabilistic methods for incorporating these different l
interpretations have been developed and used.
These "probabilistic" methods have been designed to allow explicit incorporation of different models for i
zonation, earthquake size, ground motion, and other parameters. The advantage i
of using these probabilistic methods is their ability to not only incorporate different models and different data sets, but alsr to weight them using judg-ments as to the validity of the different models and data sets, thereby providing an explicit expression for the uncertainty in the ground motion estimates and a means of assessing sensitivity to various input parameters.
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Another aovantage of the probabilistic method is that a target exceedance probability can be set by examining the probability of exceeding the seismic i
design bases of more recently licensed nuclear power plants.
The proposed revision to the regulation explicitly recognizes that there are j
inherent uncertainties in establishing the seismic and geologic design i
I parameters and allows for the option of using a probabilistic seismic hazard methodology capable of propagating uncertainties as a means to address these uncertainties. The rule further recognize; that the nature of 2ncertainty and the appropriate approach to account for it depend greatly on tne tectonic l
regime and pararaeM rs, such as, the knowledge of seismic sources, the i
existence of historical and recordeo seismic data, and the understanding of l
tectonics.
Therefore, methods other than the probabilistic methods, such as sensitivity analyses, may be adequate for some sites to account for uncertainties.
The staff has achieved an appropriate balance bctween deterministic and j
probabilistic seismic hazard evaluations in the revision of the seismic and geologic siting criteria for nuclear power plants. The key elements of this balanced approach are-i a.
Conduct site-specific and regional geoscience investigations.
I' These investigations are performed to determine spacific characteristics of the proposed site, such as, the presence or absence of potential seismic sources, capable faults, characterization of the geological rock and soil strata, earthquake history of site and environs, etc.
In addition to characterizing the site, these data are needed to verify that regional characteristics used in the LLNL and EPRI probabilistic seismic hazard assesstrants (PSHA) are valid for the proposed site.
b.
Target exceedance probability is set by examining the design bases of more recently licensed nuclear power plants.
The targc' exceedance probability is the median probability of exceeding the Safe Shutdown Earthquake (SSE) for operating nuclear power plants that were designed to Regulatory Guide 1.60 or to a l
similar spectrum. This value has been determined to be IE-5/ year j
c.
Determine if information from geoscience investigations change
[
probabilistic results.
The applicant conducts an evaluation that demonstrates that the data obtained from the site investigations (Step a. above) do not provide information that would necessitate revision of the existing seismic sources and their characteristics or attenuation models.
d.
Conduct probabilistic seismic hazard analysis and determine ground motion level corresponding to the target exceedance probability.
l The applicant condacts a LLNL or EPRI PSHA for the proposed site to obtain a seismic hazard curve, i.e., ground acceleration vs.
j annual probability of exceedance.
The hazard curve is I/3-4
deaggregated to determine a seismic event described by an average earthquake magnitude and distance (distance from earthquake to the nuclear power plant site) which contributes most to the ground motion level corresponding to the target exceedance probability.
This magnitude and distance is then used in subsequent steps to determine site-specific spectral shape.
e.
Determine site-specific spectral shaps and scale this shape to the ground motion level determined above.
The applicant will use the seismic event of magnitude and distance determined in Ster d to develop a site-specific spectral shape in accordance with SRP 2.5.2 procedures and additional guidance to be provided in draft Regulatory Guide DG-1032. The SRP procedures, in part, are based on use of seismic recorded motions or ground motion models appropriate for the event, region and site under consideration.
f.
NRC staff review of ground motion.
The NRC staff will review the applicants proposed SSE ground motion to assure that it takes into account all available data including insights and information gained from previous licensing experience.
g.
Update the data base and reassers probabilistic methods at least every ten years.
To keep the regulatory guidance on the probabilistic methods and their seismic hazard data base current, the NRC would reassess them at least every ten years and update them as appropriate.
Thus, the above proposed approach requires thorough regional and site-specific.
geoscience investigations. The proposed approach reflects some of the comments of the U.S. utility industry. The U.S. Geological Survey provided a series of comments and recommendations that led to and can be met by the above balanced approach.
Results of the regional and site-specific investigations must bc considered in application of the probabilistic method. The current probabilistic methods, the NRC sponsored study conducted by Lawrence Livermore National Laboratory (LLNL) or the Electric Power Research Institute (EPRI) seismic hazard study, are essentially regional studies withnut detailed information on any specific location. The regional and site-specific investigations provide detailed informat%;a to upi;te the database of the hazard methodology to make the probabilistic analysis site-specific. It is also necessary to incorporate local site geological factors such as stratigraphy and topography and to account for site-specific geotechnical properties in establishing the design basis ground motion.
The NRC staff's review approach to evaluate an application is described in Draft SRP Section 2.5.2.
This review takes into account the infnrmation base developed in licensing more than 100 plants. This staff review
. consistent with the intent of a USGS recommendation. Although the basic premise in j
establishing the target exceedance probability is that the current design I/3-5
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levels are adequate, a staff review further assures that there is consistency-with previous licensing decisions and that the scientific basis for decisions are clearly understood.
This review approach will also assist in assessing the fairly complex regional probabilistic modeling which incorporates multiple i
hypotheses and a multitude of parameters.
Furthermore, this process should provide a clear basis for the staff's decisions and facilitate communication with non-experts.
ELillTII()llAl{E E:NIGIP4EEIIIB0G l
The proposed regulation is a new Appendix S, " Earthquake Engineering Criteria
'or Nuclear Power Plants," to Part 50.
Procedures acceptable to the NRC staff for meeting the requirements in the regulation are contained in three draft regulatory guides, (a) DG-1033, Third Proposed Revision 2 to Regulatory Guide 1.12, " Nuclear Power Plant Instrumentation for Earthquakes," (b) DG-1034,
" Pre-Earthquake Planning and Immediate Nuclear Power Plant Operator Postearthquake Actions," and (c) DG-1035, " Restart of a Nuclear Power Plant Shut Down by a Seismic Event."
Major changes associated with the proposed regulation were de cribed in Kenneally, 1992.
Significant deviations from the cited reference are described below.
Value of the Operating Basis Earthquake Ground Motion (OBE) and Required OllE i
Analyses.
Consistent with the October,1992, version, the proposed regulation would allow the value of the OBE to be set at (a) one-third or less of the SSE, where OBE requirements are satisfied without an explicit response or design analyses being performed, or (b) a value greater than one-third of the SSE, where analysis and design are required. If an OBE of one-third of the SSE is
- used, the OBE serves the function of an inspeciion and shutdown earthquake.
There is high confidence that, at the one-third SSE ground-motion level with other postulated concurrent loads, most critical structures, systems, and components will not exceed currently used design limits. This is ensured, in part, because PRA insights will be used to support a margins-type assessment of seismic events. A PRA-based seismic margins analysis will consider sequence-level High Confidence, Low Probability of Failures (HCLPFs) and fragilities for all sequences leading to core damage or containment failures up to approximately one and two-thirds the ground motion acceleration of the design basis SSE (
Reference:
Item II.N, Site-Specific Probabilistic Risk i
Assesstuent and Analysis of External Events, memorandum from Samuel J. Chilk to James M. Taylor,
Subject:
SECY-93-087 - Policy, Technical, and Licensing i
1 Issues Pertaining to Evolutionary and Advance Light-Water Reactor (ALWR)
Designs, dated July 21, 1993.)
i In SECY-93-087, " Policy, Technical, and Licensing Issues Pertaining to Evolutionary and Advance Light-Water Reactor (ALWR) Designs," the NRC staff requested Commission approval on 42 technical and policy issues pertaining to either evolutionary LWRs, passive LWRs, or both.
The NRC staff identified I/3-6
I actions necessary for the design of structures, systems, and components when the OBE design requirement is eliminated.
Guidelines should be maintained to ensure the functionality of components, equipment, and their supports.
In addition, the staf' clarified how certain design requirements are to be considered for buildings and structures that are currently designed for the OBE, but not the SSE.
Also, the NRC staff has evaluated the effect on safety of eliminating the OBE from the design load combinations for selected structures, systems, and components ard has developed proposed criteria for an analysis using only the SSE.
Required Plant Shutdown The proposed regulation would treat plant shutdown associated with vibratory i
ground motion exceeding the OBE or significant plant damage as a condition in every operating license. A new paragraph 50.54(ee) would be added to the regulations to require a process leading to plant shutdown for licensees of nuclear power plants that comply with the earthquake engineering criteria in Proposed Appendix S to 10 CFR Part 50.
Immediate shutdown could be required until it is determined that structures, systems, and components needed for safe shutdown are still functional.
The regulation also includes a provision that requires the licensee to consult with the Commission and to propose a plan for the timely, safe shutdown of the i
nuclear power plzit if systems, structures, or components necessary for a safe shutdown or to maintain a safe shutdown are not available.
(This unavailability may be due to earthquake related damage.)
RELATED REGULATORY GUIDES AND STANDARD REVIEW PLAN SECTFIC) bus t
The NRC is dr. eloping the following draft regulatory guides and standard review plan sections to provide prospective licensees with the necessary s
guidance for implementing the proposed regulation. The notice of availability for these materials will be published in a later issue of the Federal Register.
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- 1. DG-1032, " Identification and Characterization of Seismic Sources and Determination of Shutdown Earthquake Ground Motions." The draft guide provides general guidance and recommendations, describes acceptable procedures and provides a list of references that present acceptable methodologies to i
identify and characterize capable tectonic sources and seismogenic sources.
i Section V.B.3 of this Proposed rule describes the key eitrants.
- 2. DG-1033, Third Proposed Revision 2 to Regulatory Guide 1.12, " Nuclear Power Plant Instrumentation for Earthquakes." The draft guide describes seismic instrumentation type and location, operability, characteristics, installation, actuation, and maintenarce that are acceptable to the NRC sta#f.
- 3. DG-1034, " Pre-Earthquake Planning and Immediate Nuclear Power Planc
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Operator Post-Earthquake Actions." The draft guide provides guidelines tbat are acceptable to the NRC staff for a timely evaluation of the recorded seismic instrumentation data and to determine whether or not plant shutdown is required.
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