Information Notice 2010-18, Generic Issue 199, Implications of Updated Probabilistic Seismic Hazard Estimates in Central and Eastern United States on Existing Plants
| ML101970221 | |
| Person / Time | |
|---|---|
| Issue date: | 09/02/2010 |
| From: | Mcginty T, Vonna Ordaz NRC/NMSS/SFST, Division of Policy and Rulemaking |
| To: | |
| Beaulieu, D P, NRR/DPR, 415-3243 | |
| References | |
| FOIA/PA-2011-0259 IN-10-018 | |
| Download: ML101970221 (6) | |
ML101970221 UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
WASHINGTON, DC 20555-0001
September 2, 2010
NRC INFORMATION NOTICE 2010-18:
GENERIC ISSUE 199, IMPLICATIONS OF
UPDATED PROBABILISTIC SEISMIC HAZARD
ESTIMATES IN CENTRAL AND EASTERN
UNITED STATES ON EXISTING PLANTS
ADDRESSEES
All holders of an operating license or construction permit for a nuclear power reactor issued
under Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of
Production and Utilization Facilities.
All holders of or applicants for a license (general or site specific) for an independent spent fuel
storage installation (ISFSI) issued pursuant to 10 CFR Part 72, Licensing Requirements for the
Independent Storage of Spent Nuclear Fuel, High-Level Radioactive Waste, and Reactor- Related Greater Than Class C Waste.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees about the August 2010 NRC document, Safety/Risk Assessment Results for
Generic Issue [GI] 199, Implications of Updated Probabilistic Seismic Hazard Estimates in
Central and Eastern United States on Existing Plants (Agencywide Documents Access and
Management System (ADAMS) Accession No. ML100270582 (package)), that discusses recent
updates to estimates of the seismic hazard in the central and eastern United States (CEUS).
Although not specifically evaluated as part of Generic Issue 199 (GI-199), the updated seismic
hazard estimates also apply to independent spent fuel storage installation (ISFSIs) located in
the CEUS. This includes ISFSIs that are co-located at the reactor sites, which use the plant
safe shutdown earthquake (SSE) as their design/licensing basis, as well as ISFSIs located
away from the reactor site, which have their own location-specific licensing/design-basis
earthquake. The NRC expects that recipients will review the information for applicability to their
facilities and consider actions, as appropriate. Suggestions contained in this IN are not NRC
requirements; therefore, no specific action or written response is required.
BACKGROUND
In support of early site permits for new reactors, the NRC staff reviewed updates to the seismic
source and ground motion models provided by applicants, which identified higher seismic
hazard estimates that may result in the increased likelihood of exceeding the SSE at operating
facilities in the CEUS. This seismic update included new Electric Power Research Institute
(EPRI) models to estimate earthquake ground motion and updated models for earthquake
sources in the CEUS such as around Charleston, South Carolina and New Madrid, Missouri.
The regulatory requirements that establish the seismic design bases for currently operating
nuclear power plants are 10 CFR Part 100, Reactor Site Criteria, and 10 CFR Part 50,
Appendix A, General Design Criteria for Nuclear Power Plants, Criterion 2, Design bases for
protection against natural phenomena. These regulatory requirements are fundamentally
deterministic, while the new seismic hazard information evaluated for GI-199 is fundamentally
probabilistic.
The NRC Probabilistic Risk Assessment (PRA) Policy Statement encourages the use of PRA
methods and states that PRA should be used to support the proposal for additional regulatory
requirements in accordance with 10 CFR 50.109, Backfitting. NRC regulations and guidance
such as 10 CFR 50.109 and NUREG/BR-0058, Regulatory Analysis Guidelines of the U.S.
Nuclear Regulatory Commission, provide a framework for changing regulatory positions in light
of new information. The Generic Issues Program (GIP) utilizes the backfitting and regulatory
analysis guidelines for evaluating generic issues.
Considering that estimates of the seismic hazard for some currently operating plants in the
CEUS have increased, the NRC staff reviewed and evaluated this new information along with
similar U.S. Geological Survey (USGS) seismic hazard estimates. From this review, the NRC
staff concluded that seismic design of currently operating reactor and ISFSI facilities provides
safety margin; however, the likelihood of exceeding the seismic hazard values used in plant
design and in previous evaluations may be higher than previously understood for some currently
operating CEUS sites. This review also resulted in the NRC staff issuing a memorandum, dated
May 26, 2005 (ADAMS Accession No. ML051450456), recommending that the new data and
models for CEUS seismic hazards be examined under the NRCs GIP as GI-199.
As part of its examination, the NRC staff compared the new seismic hazard data with the earlier
evaluations conducted as a part of the Individual Plant Examination of External Events (IPEEE)
program. The examination was intended to assess seismic performance of existing plants at or
beyond the design-basis level. Based on that assessment (using the seismic hazard
information available at the time of the IPEEE), the NRC staff determined that the seismic
designs of operating plants in the CEUS still provide adequate safety margins.
To follow-up with interested stakeholders, the NRC staff held a public meeting on
February 6, 2008, attended by many operating reactor licensees and EPRI representatives
(ADAMS Accession No. ML080350189), to discuss its ongoing activities related to GI-199. In
that meeting, the NRC staff described the screening process and criteria and explained the
screening analysis results (ADAMS Accession No. ML073400477).
DESCRIPTION OF CIRCUMSTANCES
The NRCs Safety/Risk Assessment Results for Generic Issue 199, Implications of Updated
Probabilistic Seismic Hazard Estimates in Central and Eastern United States on Existing
Plants, documents the two-stage assessment performed by the NRC staff to determine the
implications of updated probabilistic seismic hazard estimates in the CEUS on existing plants.
The first stage involved evaluating the change in seismic hazard with respect to previous
estimates at individual plants. The second stage estimated the change in seismic core damage
frequency (SCDF) as a result of the change in the seismic hazard for each operating plant in the
CEUS. The Safety/Risk Assessment describes the NRC staffs approach in detail. The
methodology, analyses, results, and limitations of the Safety/Risk Assessment are briefly
summarized below.
DISCUSSION
Evaluation of Changes in Seismic Hazard Estimates
In this stage, the NRC staff evaluated the potential significance of changes in seismic hazards in
a stepwise fashion by assessing the degree to which the seismic hazard estimates developed
using the most recent seismic hazard information and NRC staff guidance deviate from
previously developed assessments. The comparison of results indicated an increase in the
seismic hazard estimates relative to previous assessments for a number of plants.
Evaluation of Changes in Seismic Core Damage Frequency
In the second stage, the NRC staff developed SCDF estimates using three sets of mean
seismic hazard curves (the 1989 EPRI study, the 1994 Lawrence Livermore National Laboratory
study, and a 2008 USGS study) and plant-level fragility curves developed from information
provided in the IPEEE submittals. The changes in NRCs SCDF for a number of plants lie in the
range of 10-4 per year to 10-5 per year, which meets the numerical risk criteria for an issue to
proceed to the regulatory assessment phase of the GIP.
It should be recognized that the approach used to estimate SCDF in the Safety/Risk
Assessment does not provide insight into which structures, systems, and components (SSCs)
are important to seismic risk. Such knowledge provides the basis for postulating plant backfits
and conducting a value-impact analysis of potential backfits during a regulatory analysis. For a
number of plants, especially those that performed reduced-scope seismic margins analysis, detailed information is presently not available to the NRC regarding plant seismic capacity (the
ability of a plants SSCs to successfully withstand an earthquake) beyond the required design- basis level. CONCLUSION
(1) Operating nuclear power plants are safe. The Safety/Risk Assessment confirms that the
overall seismic risk estimates remain small for operating nuclear power plants and the
current seismic design provides a safety margin.
(2) Some seismic hazard estimates have increased. Updates to seismic data and models show
increased seismic hazard estimates for some operating nuclear power plant sites and co- located ISFSI facilities in the CEUS. New consensus seismic hazard estimates for the
CEUS will become available in early 2011 (these are a product of a joint NRC,
U.S. Department of Energy, USGS, and EPRI project). Based on this, the NRC staff has
commenced evaluating the development of a regulatory mechanism to routinely and
promptly evaluate new seismic hazard information as it becomes available.
(3) Assessment of GI-199 will continue, however, not all of the information needed to perform
the regulatory assessment is currently available to the NRC staff. The NRC will follow the
appropriate regulatory process to request operating plants and ISFSIs to provide specific
information relating to their facilities to enable the NRC staff to complete the Regulatory
Assessment. Based on results of the Safety/Risk Assessment, the NRC staff determined
that the issue should continue to the regulatory assessment stage of the GIP for further
investigation to assess whether candidate backfits should be considered for plant
improvements to reduce seismic risk and to evaluate their potential cost-justified imposition.
While these conclusions do not point to a safety concern, there were limitations to the risk
methodology employed and uncertainties associated with the data used. As such, although
there is no specific requirement, licensees of operating power reactors and ISFSI facilities in the
CEUS may evaluate whether the updated seismic hazard estimates impact their current
design/licensing basis.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
/RA by RLorson for/
/RA/
Vonna Ordaz, Director
Timothy J. McGinty, Director
Division of Spent Fuel Storage
Division of Policy and Rulemaking
and Transportation
Office of Nuclear Reactor Regulation
Office of Nuclear Material Safety
and Safeguards
Technical Contact:
301-415-2765
E-mail: Kamal.Manoly@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
ML101970221 TAC ME4039 OFFICE DE:NRR
Tech Editor
D:DRA:RES
D:DE:NRR
LA:PGCB:NRR
NAME
KManoly
KAzariah-Kribbs
CLui
PHiland
CHawes
DATE
08/25/10 e-mail
7/26/10 e-mail
8/19/10 e-mail
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8/27/10 e-mail
OFFICE PM:PGCB:NRR
BC:PGCB:NRR
D:DSFST
D:DPR:NRR
NAME
DBeaulieu
SRosenberg
VOrdaz (RLorson for) TMcGinty
OFFICE 8/24/10
8/31/10
8/31/10
9/02/10