ML20059F092

Forwards Request for Addl Info Re Fire Protection Modeling in Probability Safety Assessment.Answers to Questions Will Form Basis for 900919 Meeting in Rockville,Md

ML20059F092
Person / Time
Site:	South Texas
Issue date:	08/30/1990
From:	Dick G Office of Nuclear Reactor Regulation
To:	Hall D HOUSTON LIGHTING & POWER CO.
References
TAC-73009, TAC-73010, NUDOCS 9009110088
Download: ML20059F092 (4)

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' August 30, 1990 . -i

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DISTRIBUTION 3

%' J Docket Nos' 50-498~

Docket Filer- E. Jordan and 50-499 NRC PDR E._che111ah< i Local PDR .G. Kelly.  !

. _ D. Crutchfield ACDS (10).

1 Mr. Donald P." Hall B. Boger A. El-Bassioni ~.,

. Group Vice-President, Nuclear. C. Grimes M. Slosson

' Houston Lighting & Power' Company E.'Peyton' H. Vandermolen .,

, P. O. Box 1700- G. Dick M. Cunningham

, Houston, Texas 77251 PDIV-2 Reading M. Wohl.

• PDIV-2 Plant File J.-Wiebe i

Dear Mr. itall:

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SUBJECT:

REQUEST FOR ADDITIONAL INFORMA7 HA REGARDING FIRE PROTECTION MODELING IN THE PROBABILITY SAft(Y ASSESSMENT (PSA), SOUTH- .)

TEXAS PROJECT, UNITS 1 AND 2 (TAC NOS. 73009 AND 73010) )

By: letter dated June 18, 1990, we transmitted to Houston Lighting & Fower >

Company, the draft of the Fire Review Status Report prepared by our contractor,.

Sandia National Laboratories. Requests for additional.information were included withir.the text of.the report. The staff, in reviewing the draft report, has, N

-extracted the questions and, with some clarification, have included them in-the enclosure to this letter. These questions now supersede those either explicitly stated or implied in the draft report.

As discussed with members of your staff, we propose that the answers to the- j quet..fons form-the basis for a meeting in Rockville, Maryland. The meeting is presently scheduled to be held on September 19, 1990.

Sincerely, I I

OdginalSigned By: i l

George F. Dick,, Jr. ,. Project Manager 'J Project Directorate IV-2 I i Division of: Reactor Projects- 'III, I L IV, V and Special Projects 1 L Office of Nuclear Reactor' Regulation . I

Enclosure:

As stated i cc w/encitsure: ,

See next page i;

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IJ OFFICIAL RECORD. COPY 4

. Document N me: RAI FIRE PROTECTION MODELING /

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' 9009110008 900830 . <

ADOCK 05000498.4 I? PDR 9 PNU M

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Mr.. Donald P. Hall = - at-

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Senior Resident Inspector Jack R. Newman, Esq.  :

U.S. Nuclear Regulatory Commission Newman & Holtzinger, P.C. ,

l P. O. Box 010' 1615 L Street. N.W.

Bay City, Taxas- 77414 Washington, D.C. 20036

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Nr. J. C. Lanier Licensing Representative Director of Generation. Houston Lighting _and Power Company- i

-City of Austin Electric Utility Suite 610 L 1721 Barton Springs Road -Three Metro Center l, Austin, Texas 78704 Bethesda,-Maryland 20814 L

i Mr. R. J. Costello. Bureau of Radiation Control L Mr. M..T. Hardt State of Texas-City Public Service Board 1101 West 49th Street  :

n. P._0. Box.1771 Austin, Texas 78756 l~

San Antonio,iTexas .78296 l~- Rufus S. Scott Mr. R. P. Verret Associate General: Counsel Mr. D. E.-Ward Houston Lighting & Power Company "

Central Power and Light Company P. O. Box 61867 l P.'O. Box 2121 Houston, Texas 77208 .i l_ Corpus Christi, Texas 78403 l L.

L ~INPO l- Decoros Center 'l 1100 Circle 75 Parkway l

' Atlanta, Georgia 30339-3064. =

l Regional Administrator, Region IV e

U.S. Nuclear Regulatory Commission 611'Ryan Plaza Drive,. Suite'1000-P

-. Arlington, Texas 76011 :l IMr. Joseph M. Hendrie 50 Bellport Lane-j Be11 port, New York 11713 l Judge,-Matagorda. County-

.i Matagorda County Courthouse '

11700 Seventh Street Bay _ City, Texas 77414 s

Mr. M..A. McBurnett l

.  : Manager, Operations-Support Licensing 3 Houston' Lighting & Power Company l- P. O. Box 289' l

_W adsworth, Texas 77483 l'

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b 4f SOUTH; TEXAS PROJECT, UNITS l'AND 2 7 i,

DOCKET N05. 50-498 AND 50-493

i REQUEST FOR ADDITIONAL INFORMATION 1 FIRE PROTECTION MODELING 1 SOUTH TEXAS PSA 1 t

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The following is a list of additional questions which have resulted from the l review of the licensee's response to our previous questions in the areas of fire r.sk. 1 l

1. _The staff observes that the combined reduction factors (a combination of  :

assigned geometry factors and severity factors) documented in Table 9.3-8 L seem to be lower than those documented in other PRAs. For example, the 1 L c reduction factor used for 4.16KV switch gear rooms seem to be substantially I

. lower than used in the Diablo Canyon PRA (1,0) and NUREG-1150 risk analyses.- H' Based on a review of existing deterministic fire analyses (such as-areas of cable location identification, postulated cable (and other transient combus-tible s) burn and/or heat load calculations, associated time dependent

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l suppiession probability distributions) provide the basis for the appro- i priateness of the use of these reduction factors for the critical fire zones,. ,

l' including the 4.16KV switch gear room. If no supporting analyses exist at , 1 l' this time, the licensee should provide detailed rationale (zone-specific.

qualitative arguments) regarding the applicability of the reduction factors

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used for all critical fire zones. Sensitivity analyses of the assignment' 5 of higher combined reduction factors to each fire' zone to develop perspec- . J tives of-the impact on overall core damage frequency could be used to_ support-t_ 'the qualitative arguments.

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2. For control room fire scenario (Scenario 6),_the licensee,has assigned a i severity factor in the range of 0.072 to 0.0015 to evaluate the propagation l L characteristics of the postulated cabinet (panel) fires. Experimental tests- L conducted at SNL have shown that a postulated panel fire could virtually.

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damage the entire panel within a relatively 'short period of time (e.g. , five minutes). Thus, the staff questions the licensee's assignment of the lower 1 severity factor for the panel fires (relative to those used in the Diablo l Canyon PRA and NUREG-1150 risk analyses). Therefore, the licensee should j l provide a detailed rational (qualitative arguments)~regarding the assignment l L of the lower severity factors for the panel-fires. These rationales-should .i

.not be_ limited to panels located only in the control room. )

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3. It is noted that the statements (refer te pages 8.5-15 and 9.4-1) 1 regarding the dominant contributor (panel fires as opposed to' transient '

combustible fires) to the initiating' frequency of_ the control room fires (4.08E-3 per reactor year) appear to be' inconsistent. Current operating ]

l reactor experience shows'that the panel fires dominate the initiating' l event frequency of-the control room fires. Provide clarifications )

H1 regarding the above apparent inconsistent statements made in the PRA. 1

4. For fire scenario Z004-FS-01, provide the derivation procedure used for l l- the initiating fire frequency, discussions related to assignment of an additional random faiiure (0.01) in resulting sequences, and discussions l related to other additional failures assumed prior to screening. '

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5. On page 9.3-4 of the PRA, the second level of fire screening is stated to be at a frequency of 2.0E-7/yr. In Table 0,3-9 of the PRA.11 out of the 24 andstates are apparently screened using this criteria. While this criteria by itself has not completely eliminated the fire area given in the example, it did significant'y contribute to its elimination in that approximately 50 percent of the wudstates were screened. Provide the basis for the selection of 2.0E-7 as the screening critoria.

6. On page 9.3-4 of the PRA, endstates are quoted as being scenened at 10 percent of the equivalent internal event frequency. Referring to the example given in Chapter 9 of the PRA, approximately one-third of the fire area endstates are screened by this (10 percent) criteria. It must be noted that typically much more chance for recovery exists for internal event failures as compared to fire-related failures. Therefore, the potential exists that if further development of the fire scenarios occurred their relative contribution with respect to similar internal events endstates

. might be significantly altered. Provide the rationale for the selection of the screening criteria of 10 percent.

7. In response to previous questions (HL&P letter ST-HL-AE-3414), the licensee stated that the total core damage frequency resulting from fire-initiated events is approximately 5.0E-7/yr. Da page 9.4-23 of the PRA, a simple summation of control room core d. mage frequency yields 8.02 E-7/yr. Explain this difference.

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