ST-HL-AE-5280, Forwards Revised Table to ,Deleting Item for Hydrogen Analyzers & Revised Table to ,Revising Column Heading.Stp PSA Info Re Containment Isolation Also Encl

Forwards Revised Table to ,Deleting Item for Hydrogen Analyzers & Revised Table to ,Revising Column Heading.Stp PSA Info Re Containment Isolation Also Encl

ML20097H147
Person / Time
Site:	South Texas
Issue date:	01/23/1996
From:	Leazar D HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-5280, TAC-M92169, TAC-M92170, NUDOCS 9601290283
Download: ML20097H147 (11)

Text

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a The light l company seeth Tesas Project Dectric Generating Station P.O. Box 289 Wadsworth, Tesas 7,483 Houston rJghting & Power 1996 January ST-HL-AE-5 23'280 FileNo.: G20.02.01 1 10CFR50.90,50.92 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 South Texas Project Units 1 and 2 Docket Nos. STN 50-498; STN 50-499 l Additional Information Regarding Proposed Special Test Exception 3.10.8 (TAC No. M92169/M92170)

References:

1. Letter from D. A. Least to the Nuclear Regulatory Comnussion Document I Control Desk dated January 4,19')6 (ST-HL-AE-5261)

2. Letter from D. A. Leazar to the Nuclear Regulatory Commission Document  ;

Control Desk dated January 8,1996 (ST-HL-AE-5272)

I As a result ofconversations with the NRC Staff, the South Texas Project has revised the table g attached to Reference I to delete the item for Hydrogen Analyzers and the table attached to Reference 2 to revise a column heading. The revised tables are attached. Also attached is South Texas Project Probabilistic Safety Assessment information regarding containment isolation that was previously  ;

provided to the NRC Staffinformally.

Should you have any questions, please contact Mr. A. W. Harrison at (512) 972-7298 or me at (512) 972-7795.

b . C. -

D. A. Leszar /

Director, NuclearFueland Analysis FCK/

Attachments:

1. Replacement Table for ST-IIL-AE-5261

2. Replacement Table for ST-HL-AE-5272

3. PSA Information re Containment Isolation 9601290283 960123 PDR ADOCK 05000498 P PDR AliVi '

i,

. .s .

1 Houston Lighting & Power Company ST-HL-AE-5280 South Texas Project Electric Generating Station File No.: G20.02.01 Page 2 c: i Leonard J. Callan Rufus S. Scott

. Regional Administrator. Region IV Associate General Counsel U. S. Nuclear Regulatory Commission Houston Lighting & Power Company )

611 Ryan Plaza Drive, Suite 400 P. O. Box 61067 ,

Arlington, TX 76011-8064 Houston, TX 77208 '

Thomas W. Alexion Institute of Nuclear Power i Project Manager Operations - Records Center I

- U. S. Nuclear Regulatory Commission 700 Galleria Parkway 1 Washington, DC 20555-0001 13H15 Atlanta, GA 30339-5957 David P. Loveless Dr. Joseph M. Hendrie Sr. Resident Inspector 50 Bellport Lane  ;

c/o U. S. Nuclear Regulatory Comm. Bellport, NY l1713 l P. O. Box 910 Bay City, TX .77404-0910 Richard A. Ratliff Bureau of Radiation Control J. R. Newman, Esquire Texas Department of Health Morgan, Lewis & Bockius 1100 West 49th Street 1800 M Street, N.W. Austin, TX 78756-3189 i Washington, DC 20036-5869 U. S. Nuclear Regulatory Comm.

K. J. Fiedler/M. T. Hardt Attn: Document Control Desk City Public Service Washington, D. C. 20555-0001 P. O. Box 1771 San Antonio, TX 78296 J. C. Lanier/M. B. Lee J. R. Egan, Esquire City of Austin Egan & Associates, P.C.

Electric Utility Department 2300 N Street, N.W.

721 Barton Springs Road Washington, D.C. 20037 Austin, TX 78704 Central Power and Light Company J. W. Beck ATTN: G. E. Vaughn/C. A. Johnson Little Harbor Consultants, Inc.

P. O. Box 289, Mail Code: N5012 44 Nichols Road ,

Wadsworth, TX 77483 Cohassett, MA 02025-1166

Attachment 1 -

ST-HL-AE-5280 Page1of3 ,

Systems with Reduced Design Basics Capability in Single Train Operation SYSTEM FUNCTION ALTERNATIVE EVENT COMMENTS AFFECTED ACTION PROBABILITY t M MdWM@M En DR$$ W R91L% G $$4 Safety Cannot mitigate None(minimalcooling 1.91E-10 One trainin the STE Injection (LHSIand LBLOCAif the SItainis from using hotleg Onetraininopemble injectinginto the broken recirculation) Note: Accountsfora One traininjectsinto the HHSI)

RCS loop 25% chance ofinjectingin brokenloop brokenloop Leakbefore break not credited SafetyInjection Steamline break None required 2.25E-8 DNB not expected to (HHSI) mitigation capability occur reduced Note: Accountsfora rupture eitherinside or outside containment Safety Injection (LHSI Cannot mitigate SBLOCA Operator action per EOPs 1.75E-9 One trainin the STE and HHSI) without operatoractionif to depressurize One traininoperable the SI trainisinjecting Note: No credit taken for One train ofHHSInot into the broken RCSloop operatoraction to enough to match break depressurize flow Operatoractionis expected to be effective ResidualHeat Removal Cannot providelongterm Continue toiniect using See Comments RHRis required coolingifonly a single LHSIuntilRHRis approximately 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> ESF busis enasmiorif restored. afterevent. Recoveryof RHRisinjectmginto powerto ESF busis '

broken loop expected within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />

Attachment 1 .

ST-HL-AE-5280 Page 2 of 3 ,

SYSTEM FUNCTION ALTERNATIVE EVENT COMMENTS AFFECTED ACTION PROBABILITY t BRisntM?s %hWM @ % % i 4 @ $iE? dI@ $ $1 WNOiWM&X iSffi34MM9; Conta.inment Spray Iodine removalduringa MonitorTSC doses and 1.97E-8 LBLOCAor SBLOCA relocate tolower dose area Note: Assumingmost probable event of SBLOCA ControlRoom Envelope. Cannot maintain 1/8" Positive pressureis 7.64E-10 HVAC positive pressure expected to be ined so systemis Note: Hisisthe expected to be functional probability ofa LBLOCA, failure ofDG and LOOP whilein the STE FuelHandhngBuilding Cannot provide filter path Provide attemate power 637E-11 HVAC for recirculation phase supply from operable leakageifC trainis only diesel Note: Duetodesign operable train dependencies probabilities are calculated based on trains Aor B being operable

Attachment 1 -

ST-HL-AE-5280 Page 3 of 3 ,

SYSTEM FUNCTION ALTERNATIVE EVENT COMMENTS AFFECTED ACTION PROBABILITY t Component Coohng CCW flow to RCFC's and - Manually isolate non- 5.75E-5 Iftrain Cis the operable Water RHR Heat Exchangerless safetyheaderto restore train, CCW flow than design design flow. Note: Accountsforthe approximates design ficw.

pul isstyoftrain C Effect ofreduced CUV isolating non-safety flows flowis slight even witnout manual action.

Hydrogen Recmulaners Cannot use Hydrogen See Comments Not required until RecombinersifAis only approsnately 11 days operable train after accident Recovery ofpownto ESF busis expected within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> t The ewmt probability is the likelihood of an initiating event (i.e., Large Break LOCA) with a loss ofoffsite power and failure of a standby diesel generator given a diesel generator is unavailable for the whole 21 days ofthe STE. It conservatively does not include recovery factors or support system failures.

Attachment 2 -

ST-HL-AE-5280 Page1of1 ,

CONTAINMENT PRESSURE / TEMPERATURE ANALYSIS LIST OF ASSUMPTIONS LOCA MSLB Single ESF-Train Muhiple ESF-Trains Single ESF-Train Multiple ESF-Trains Double Ended Pump Suchon Doubic Ended Pump Suctxm 102% Power,MSIV Failure 1025 Power,MSIV Faihue Guillonne with Muumum Guillonne with Maximum with Muumum Cun . a with Maximum Cub..es Safayinjeaxm and Safetyinjecuan and Heat RenxnalS 3stems in Heat RenunalS3stemsin Minunum Contausnent Heat Minimum Cuw.o.ict Heat Operanon Operanon Removals3stemsin Removal Systemsin Operanon Operation NumberofSpraytrain 1 2 1 3 ssu.ing Spray fkmTate 1885 gpm 3800 rpm 1885 gym 4700 rpm Spray initianon time 140 sec 82.6 sec 140 sec 90.6 see Numberof RCFC trains l 2 1 3 uru. tug Number of RCFCs 1 3 1 5 RCFC initiatxm time 66.1 sec 38 sec 67.7 sec 67.7 see CCW Em.pci.Eae 125*F 110*F 125*F 110*F CCW fknvto each RCFC 1600 rpm 1800 rpm 1600 gym 1800 rpm Total CCW flow to all 1600 gpm 5400 gpm 1600 gpm 9000 gpm RCFCs usaiin the anahsis

Attachment 3 ST-HL-AE-5280 J

Page1 of5 Attachment 3: PSA Information re Contain:nent Isolation PSA vs to questions from the phone conference between HL&P and the NRC on 1/3/96 with respect to the November 22nd supplemental response regarding the proposed Special Test Excepten (ST-HL-AE-5208):

Question Concerning answer to question #7a, please explain why the values cited doni agree with values in table 3.1-4 of May 1st submittal (ST-HL-AE-5076)? What are large and small early release values without the Special Test Exception, based on 1995 PSA?

Response 'Ihe values presented in the response to question #7a are an input into calculatmg the l Large and Small Early Release frequencies. Question #7a requested a comparison of the l containment isolation failure frequency with and without the requested technical specification change The frequencies associated with Table 3.1-4 represent the release frequencies in the STP PSA for LERF and SERF and were not intended to reflect the contribution of contamment isolation failures to LERF/ SERF. The contamment isolation failure frequency, as modeled in the STP PSA, is based on the failure of top events CI and CP. The quantified values used for these top events are uased on a level 1 PSA analysis which calculates the frequencies of plant damage states that are linked to the Ce6 ment Event Tree (CET) for the Imel 2 evaluation. The CET defines and quantifies accident progression from the Level I plant damage states to the Level 2 end states which are referred to as release categories. 'Ihe quantified release categories define the frequency, characteristics, timing and magnitude of radiological releases (e.g., LERF or SERF) from the plant ,

l deyceding on the plant response of severe accident phenomena and containment performance.

The table faxed on 1/3/96 for the phone conference was in error. This faxed table provided an update to Table 3.1-4 of the May 1st submittal that includes the Rebaslined (1995 PSA) release categories. The correct results are presented in the attached Table 1, which provides frequency values for the release categories of the Rebaseline model (i.e.,1995 PSA) along with the frequency j values for the release categories for the proposed Special Test Exception.

i

Attachment 3 ST-HL-AE-5280 Page 2 of 5 ,

Table 1 : Update for Table 3.1-4 of the May 21,1995 sutmuttal to include level 2 results for the Reh=h Model AN Frequency Major Fhe Group ( peryear) 1992 level 2 1993 Risk Based 1995 1995 PSA Fracten of PSA/IPE Sulmuttal Evaluation Rebaseline With 1992 Risk (STPPMT) PSA Proposed Based (STPBASE) Changes Evalumbon (STPPSA495) 1 - Large Early Contamment Failure or Bypass 9.89E-7 1.3E-6 3.49E-7 5.07E-7 0.51 .

11 - Small Early Contamment Failure or Bypass 6.67E-6 . 7.9E-6 4.14E-6 5.56E-6 0.83 l 111 - Late Contamment Failure 1.08E-5 1. lE-5 1.34E4 1.39E-6 0.54 i

IV -Intact Contamment 2.56E-5 2.7E-5 1.35E-5 1.35E-5 0.52 Total Core Damage 4.41E-5 4.7E-5 1.93E-5 2.10E-5 0.48  :

i l

l s

_________._______.____m__ _ _ _ , _ _ _ _ . _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ . _ _ . _ _ _ _ _ _ _ _ . _ _ . _ _ _ .

Attachment 3 ST-HL-AE-5280 Pe;;;e 3 of 5 Question Concerning answer to question #70 of ST-HL-AE-5208: De response implies LERF is 5 times as large as SERF. However, this doesn't seem to be the case, based on the answer to question #7a. Please explain why not? l i

Response De table provided in the response for question #7b provided the percentage contributions for each modeled penetration to the total sum of the containment isolation failure frequency. This was done by l summing the fault tree cutsets containing those basic events associated with each modeled penetration over the sum of all cutsets for all modeled penetrations. This table w3s not intended to re81ect the contribution of a particular penetration to a release category (i.e., LERF/ SERF) but was only intended to reflect the contribution of each penetration to contamment isolation failure frequencies.

Based on the conference call on 1/3/96 additional information relative to penetration contributions to )

containment isolation failure frequencies is provided as follows:

De question proposed from the phone conference on 1/3/96 was "What are the values for the percentage contributions to the response for question #7b? How do these values relate to the containment isolation failure frequency?"

Table 2 below presents the probabilistic importance value for ach of the modeled containment penetrations  !

in the PSA. As stated in the response for question #7a, the containment failures are modeled in the PSA as l Top Events CI (<3") and CP (>3"), which are defmed as failure to close at least one valve in each modeled l penetration. De values presented in Table 2 below do not directly correlate to the percentages presented in the response to question #7b of the November 22nd supplemental response. Question #7b of the November 22nd supplemental response requested "a list of the penetrations with greatest contribution to containment isolation failure frequency and their respective contributions." To further enhance the respond to question

1. 7b of the November 22nd supplemental response, two approaches have been used to correlate penetration contributions to those plant damage states where containment isolation has failed. The approach reflected in the November 22nd supplemental response was to provide a weighted average contribution of each PSA-modeled penetration to the total containment isolation failure frequency, his was done by multiplying the fractional importance of split fractions associated with containment isolation failure times their respective fault tree cutset values. The second approach differs from the first approach in that the second approach calculates the probabilistic importance of a penetration by multiplying fractional importance of split fractions associated with containment isolation failures and their respective cutset importance. Again, it should be noted that these values are based on a Level 1 analysis and do not progress through the Containment Event Tree. Therefore, the values are not intended to be compared to radiological release frequencies (i.e., LERF, SERF).

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Attachment 3

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ST-HL-AE-5280 Page 4 of 5 The probabilistic importance values in Ta.ble 2 reflect the importance of the modeled penetrations to those plant damage states where containment isolation failure has independently occurred.

Table 2: Penetration Importance Penetration Probabilistic Importance Containment Normal Sump Drain Line (Top Event CI) 1.42E-5 Supplementary Containment Purge Supply and Exhaust (Top 7.09E-3 Event CP)

Letdown and Seal Return Lines (Top Event CI) 3.53E-5 Radiation Monitoring (Top Event Cl) 3.81 E-5 RCDT to LWPS Hold Tank (Top Event CI) 2.42E-5 RCS Pressuriser Relief Tank Vent (Top Event CI) 2.24 E-5 Reactor Coolant Drain Tank Vent (Top Event CI) 1.27E-5 Pre-existing Small Leak (Top Event CI) 1.74E-3 As can be seen from the table, the supplementary containment purge supply and exhaust line represents the only contribution for Top Event CP. Failure of Top Event CP represents a special case were the failure mode occurs during a required purging of the containment; otherwise, the valves are in their fail safe position (i.e., closed). The dominate contributor for the supplementary purge line is the fraction of time the purge valve is modeled to be open. This is very conservatively modeled in the STP PSA as 2.3E-l. The assumption behind this value is based on an October 1988 letter that utilized some early plant specific operating history.

More recent data indicates that Unit I purges the containment on a regular basis every 3 days for 25 - 30 minutes (i.e.,5 to 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> per month). If the average is assumed to be 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> per month, the yearly total would be 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or 3 days which translates into a fraction of time of 8.2E-3 (i.e., 3/365). Note, Unit 2 does not purge as often as Unit 1. The purges are required in order to satisfy Technical Specifications.

From this analysis it is shown that the current PSA model is very conservative with respect to containment purges. This conservatism impacts the Large Early Release Frequency (LERF). It is STP's intention to update the fraction of time the supplementary valve is open during the next plant specific data update.

The containment isolation failure frequency represented by Top Event CI includes all the other penetrations and the small pre-existing leak term. The probabilistic importance of the pre-existing small leak term was obtained by multiplying the fractional importance of all the split fractions that contain the pre-existing small leak term times the probability of having a pre-existing small leak. As can be seen in Table 2, it is more probable to have a small pre-existing leak than an independent failure of any penetrations modeled in Top Event Cl.

The following analysis is presented in order to relate the probabilistic importance of the individual penetrations to the their respective containment isolation failure frequencies. Note, the containment isolation failure frequency (i.e., Top Event frequency) is obtained by multiplying the group frequency by the total importance of the containment isolation failure. The group frequency is obtained from the

Attachment 3 ST-HL-AE-5280 Page 5 of 5 l I

sequence database and is the sum of all the sequence frequencies mapped to core damage. The total unportance is the sum of the probabilistic importance and the guaranteed failure importance The 4

probabilistic importance is the i%t occurrence of a containment isolation failure and is obtained by summing the penetration importance values presented in Table 2. The guaranteed failure importance is based upon a containment isolation failure due to a support system. (e.g., no signal to isolate the valve) and

is obtained from the sequence database. The calculated Containment Isolatica Failure Frequencies are

presented in the sixth column of Table 3. The values in the last column represent the containment isolation failure frequency obtained frcm the STP PSA model. Table 3 represents the mathematical process for calculating the Containment Isolation Failure Frequewy from the penetration probabilistic importance value.

Table 3: Values for comparmg Penetration Contributions to the Contamment Isolation Failure Frequency a Top Probabilistic Guaranteed Probabilistic Group Calculated Containment Event importance Importance plus Frequency Containment Isolation Guaranteed Isolation Failure Failure Frequency Frequency I (A) (B) (A + B) (C)

(A+B)*C CI 1.89E-3 0.33 0.33 1.82E-5 6.04E-6 6.12E-6 CP 7.09E-3 0.0 7.09E-3 1.82E-5 1.29E-7 1.27E-7

The differences in the last two columns of Table 3 between the calculated values and the Containment isolation Failure Frequencies obtained from the STP PSA is attributed to the simplicity used in calculating the probabilistic importance for the individual penetrations.

As a final nom, the group frequency is a subset of the Core Damage Frequency (CDF). The group frequency represents the portion of the total frequency (i.e., CDF) saved to the sequerce database. This is

. referred to as the ' accounted for' frequency. The other portion of tim CDF is the ' unaccounted for' frequency that represents the portion of the CDF truncated from the sequence database. Therefore by definition, the CDF is equal to the sum of the ' accounted for' and ' unaccounted for' sequence frequencies mapped to core damage.

4 4