ML20057A012

Forwards Safety Evaluation Concluding That Licensee Has Demonstrated That External Events Not Major Contributor to Core Damage Scenarios at Plant,Per Review of External Events Portion of Licensee PSA

ML20057A012
Person / Time
Site:	South Texas
Issue date:	08/31/1993
From:	Kokajko L Office of Nuclear Reactor Regulation
To:	Cottle W HOUSTON LIGHTING & POWER CO.
Shared Package
ML20057A013	List: ML20057A012 ML20057A016
References
TAC-M73009, TAC-M73010, NUDOCS 9309100284
Download: ML20057A012 (3)

Text

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. E 1*I i E UNITED STATES Q2g c ,#

j NUCLEAR REGULATORY COMMISSION wAssincrow. o.c. mossscooi

• • • • • August 31, 1993 Docket Nos. 50-498 and 50-499 Mr. William T. Cottle Group Vice-President, Nuclear Houston Lighting & Power Company South Texas Project Electric Generating Station P. O. Box 289 Wadsworth, Texas 77483 I

SUBJECT:

EVALUATION OF PROBABILISTIC SAFETY ANALYSIS - EXTERNAL EVENTS FOR SOUTH TEXAS PROJECT, UNITS 1 AND 2 (TAC NOS. M73009 AND M73010)

Enclosed is the safety evaluation (SE) on the external events portion of the '

South Texas Project (STP) Probabilistic Safety Analysis (PSA). This review was undertaken to determine that the external events portion of the PSA was sufficiently complete in its scope so that its findings could be accepted.

Since the seismic hazard and most of the other external events at STP are not significant from the core damage point of view, and the results of the PSA do not show major contributions for external events, the staff review of the external events portion of the PSA was limited.

The staff's review concludes that the contribution of external events to the

^otal core damage frequency (CDF) is insignificant. The relatively low contribution from external events is due to: (1) the physical separation of the 3-train systems; (2) the modern design of the plant; and, (3) the relatively low initiation frequency for external events at STP.

The seismic contribution to the total CDF (estimated to be 1.7E-04/ year) was calculated to be between 0.1 percent and 12 percent, depending on the hazard curves used (i.e., Electric Power Research Institute or Lawrence Livermore National Laboratory, respectively). The staff found that the fragility approach used by the licensee, which has been used in other PSAs, is acceptable, and that the analysis of seismic events identified no significant weaknesses. Additionally, on the basis of the licensee's analysis and current data for the site, the staff further concludes that the impact of other external events (e.g., high winds, floods, turbine missiles, aircraft crashes and other transportation accidents) are insignificant.

The staff believes that the external events portion of the PSA, in conjunction with the supplemental information developed during its review, can be used in support of regulatory or licensing decisions. However, it is stressed that the staff review was limited, and that the evaluation is primarily a scoping evaluation. In general, any licensing action proposed by you that incorporates arguments based on the PSA results needs to be accompanied by detailed information on the application of the PSA to the specific issue under evaluation. Additionally, this SE does not constitute an IPEEE review and 93091002s4 DR 930831 p ADOCK 0500049a 6

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Mr. William T. Cottle 2- August 31, 1993 the IPEEE review will be conducted separately. However, this SER contains an evaluation of many IPEEE topics and should provide a basis for that review. .

This completes cur activities under TAC Nos. M73009 and M73010. I i

Sincerely, Original Signed By  ;

Lawrence E. Kokajko, Senior Project Manager '

Project Directorate IV-2 Division of Reactor Projects III/IV/V i Office of Nuclear Reactor Regulation i

Enclosure:

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- l Mr. William T. Cottle August 31, 1993 .

cc w/ enclosure: l Mr. David P. Loveless Jack R. Newman, Esq.

Senior Resident inspector Newman & Holtzinger, P.C.

U.S. Nuclear Regulatory Commission 1615 L Street, N.W.

P. O. Box 910 Washington, D.C. 20036 Bay City, Texas 77414 Licensing Representative Mr. J. C. Lanier/M. B. Lee Houston Lighting and Power Company City of Austin Suite 610 ,

Electric Utility Department Three Metro Center 721 Mrton Springs Road Bethesda, Maryland 20814 ,

Ausi h , Texas 78704  ;

, Bureau of Radiation Control l

Mr. K. J. Fiedler State of Texas l l Mr. M. T. Hardt 1101 West 49th Street I City Public Service Board Austin, Texas 78756 i P. O. Box 1771 San Antonio, Texas 78296 Rufus S. Scott  :

Associate General Counsel

Mr. D. E. Ward Houston Lighting and Power Company '

! Mr. T. M. Puckett P. O. Box 61867 Central Power and Light Company Houston, Texas 77208 1 P. O. Box 2121 Corpus Christi, Texas 78403 INPO Records Center ,

700 Galleria Parkway Atlanta, Georgia 30339-3064 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 1000 Arlington, Texas 76011 Mr. Joseph M. Hendrie i 50 Bellport Lane  :

Bellport, New York 11713 j Judge, Matagorda County  :

Matagorda County Courthouse l 1700 Seventh Street Bay City, Texas 77414 Mr. James J. Sheppard General Manager, Nuclear Licensing Houston Lighting and Power Company ,

P. O. Box 289 i Wadsworth, Texas 77483 l

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