Information Notice 2010-18, Generic Issue 199, Implications of Updated Probabilistic Seismic Hazard Estimates in Central and Eastern United States on Existing Plants.

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)

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

Kamal Manoly, NRR

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 8/26/10 e-mail 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