NOC-AE-03001631, Clarification of Response to NRC Questions Regarding a Proposed License Amendment to Eliminate the Turbine Missile Design Basis

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Clarification of Response to NRC Questions Regarding a Proposed License Amendment to Eliminate the Turbine Missile Design Basis
ML033170295
Person / Time
Site: South Texas  STP Nuclear Operating Company icon.png
Issue date: 11/06/2003
From: Jordan T
South Texas
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
NOC-AE-03001631, STI: 31670354
Download: ML033170295 (16)
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Text

tamb- AI N1 Nuclear Operating Company South Teas Profed Ekclnc Gein 5 Sttio PO. Sar 28.9 Widsith. Tas 77483 November 6, 2003 NOC-AE-03001631 I OCFR50.90 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852 South Texas Project Units 1 & 2 Docket Nos. STN 50-498, STN 50-499 Clarification of Response to NRC Questions Regarding a Proposed License Amendment to Eliminate the Turbine Missile Design Basis

Reference:

1. Letter dated November 14, 2002 from J. J. Sheppard, STPNOC, to NRC Document Control Desk, "Proposed License Amendment to Eliminate the Turbine Missile Design Basis" (NOC-AE-02001335)
2. Letter dated October 30, 2003 from T. J. Jordan, STPNOC, to NRC Document Control Desk, "Response to NRC Questions Regarding a Proposed License Amendment to Eliminate the Turbine Missile Design Basis" (NOC-AE-03001605)

In Reference 1, STP Nuclear Operating Company (STPNOC) proposed to amend the operating licenses for South Texas Project Units 1 and 2 to delete the UFSAR turbine missile design basis.

STPNOC has determined that the turbine missile contribution to risk is so small that no special measures are required beyond normal commercial operating practices.

Reference 2 responds to several NRC staff questions regarding this submittal. This submittal clarifies information in Reference 2 and provides additional information to facilitate the staff's review. Changes to the information in Reference 2 are indicated by change bars in the margin.

A001 03001631(Turbine Missile Elimination RAI clarification).DOC STI: 31670354

NOC-AE-03001631 Page 2 If there are any questions, please contact Mr. A. W. Harrison at 361-972-7298 or me at 361-972-7902.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on: NoyerA br? GCz0 Vice President Engineering & Technical Services awh Attachments:

1. Responses to Request For Additional Information on STPNOC's Request to Eliminate the Turbine Missile Design Basis South Texas Project (STP), Units 1 & 2
2. Conditional Core Damage Probability Given a Turbine Missile Is Generated

NOC-AE-03001631 Page 3 cc:

(paper copy) (electronic copy)

Bruce S. Mallett A. H. Gutterman, Esquire Regional Administrator, Region IV Morgan, Lewis & Bockius LLP U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 L. D. Blaylock Arlington, Texas 76011-8064 City Public Service U. S. Nuclear Regulatory Commission David H. Jaffe Attention: Document Control Desk U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike R. L. Balcom Rockville, MD 20852 Texas Genco, LP Richard A. Ratliff A. Ramirez Bureau of Radiation Control City of Austin Texas Department of Health 1100 West 49th Street C. A. Johnson Austin, TX 78756-3189 AEP Texas Central Company Jeffrey Cruz Jon C. Wood U. S. Nuclear Regulatory Commission Matthews & Branscomb P. 0. Box 289, Mail Code: MN116 Wadsworth, TX 77483 C. M. Canady City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704

Attachment I NOC-AE-03001631 Page 1 REQUEST FOR ADDITIONAL INFORMATION ON STPNOC'S REQUEST TO ELIMINATE THE TURBINE MISSILE DESIGN BASIS SOUTH TEXAS PROJECT (STP), UNITS 1 & 2

1. Please provide the following information about the turbine blade missile event of January, 2003:
a. Please include (i) a sketch of a top view showing the strike zone, the turbine, the safety-related essential cooling water (ECCW) buried piping, and the portion of the diesel generator building inside the strike zone; (ii) the exiting and landing locations of the broken turbine blade; and (iii) the weight of the broken turbine blade.

The STP turbine blade ejection event occurred on December 15, 2002.

(i) STP UFSAR Figure 3.5-1 is a depiction of the strike zones. The Diesel Generator Buildings (DGB) are labeled on the figure, by the southeast corner of their respective unit's Turbine Generator Building. ECW buried piping runs from the ECW Intake Structure (shown in the northeast quadrant of the site protected area) to the Unit 1 and Unit 2 Mechanical Auxiliary Buildings and the Unit 1 and Unit 2 DGBs.

(ii) The blade was ejected from the low pressure turbine into the condenser.

No ECW buried piping or parts of the diesel generator building were in the vicinity of the blade's impact.

(iii) The weight of the blade was 44 pounds.

b. If the damaged piping is ECW piping or if structures, systems, and/or components (SSCs) that are credited in the probabilistic risk assessment (PRA) were damaged, provide an assessment of the damage.

No ECW piping or other components credited in the PRA were damaged.

c. Provide a plant-specific turbine missile frequency estimate based on this and all previous STP plant-specific turbine missile incidents and actual reactor years for both units.

The turbine missile event described in the STP UFSAR is a turbine disk or fragments of a turbine disk being ejected through the turbine casing. The design basis is in accordance with SRP 3.5.1.3, "Turbine Missiles" and meets the intent of R.G. 1.115, Rev.1, "Protection Against Low-Trajectory Turbine Missiles". The design basis requirements are for large missiles as discussed in the STP UFSAR. R.G. 1.115 states:

This guide addresses only large missiles that might be ejected in the event of a turbine failure. The inherent protection provided in most plants (generally 1 1/2 to 2 feet of reinforced concrete) ensures that minor missiles, which could be ejected NOC-AE-03001631 Page 2 in significant numbers and in widely scattered directions once the casing is breached, would not result in damage to essential systems.

The event described above was a turbine blade, which did not penetrate the turbine outer casing. There have been no main turbine missile events at STP and no other main turbine blade ejections. Consequently, the event described above had no effect on the turbine missile frequency estimate.

2. Please confirm that it is your intention to eliminate all current limiting conditions for operation (LCOs), surveillance requirements (SRs), and the turbine system maintenance program described in the updated final safety analysis report (UFSAR)

Section 3.5.1.3.4.

There are no Technical Specification LCOs or SRs affected by the proposed change.

STPNOC intends to delete the LCOs and SRs governing turbine overspeed protection from the Technical Requirements Manual (TRM). In addition, STPNOC intends to delete the UFSAR references as described in the original application of November 14, 2002.

Although these descriptions and requirements will be deleted from the licensing documents, STPNOC plans to continue to maintain the turbine and provide adequate protection from overspeed and its consequences through its normal commercial programs. For instance, STPNOC has implemented additional turbine vibration monitoring as a result of the blade ejection event.

a. Please identify all the SSCs included in these current LCOs, SRs, and maintenance programs for which the programs in the UFSAR will be eliminated.

The components affected in the TRM LCOs and SRs are:

1) Four high pressure turbine stop valves
2) Four high pressure turbine governor valves
3) Six low pressure turbine reheat stop valves
4) Six low pressure turbine reheat intercept valves
5) The electrical and mechanical turbine overspeed protection STPNOC does not plan to actually eliminate any maintenance programs. The proposed change will allow STPNOC to manage the frequency and scope of the maintenance programs outside of regulatory considerations for turbine missile generation.
b. Discuss your "maintenance and monitoring program for the turbine for commercial reasons." Identify elements of the maintenance and monitoring program which serve the same purpose and function of the turbine system maintenance program that you proposed to eliminate. Demonstrate that, without the turbine system maintenance program, your turbines will still have sufficient safety margins, and consistency with the defense-in-depth philosophy will still be maintained through meeting General Design Criteria 4 requirements.

Attachment I NOC-AE-03001631 Page 3 As discussed above, STP does not plan to eliminate the turbine maintenance and monitoring program. It will no longer be governed by criteria described in licensing documents. STP may elect to change the frequency or scope of inspections of the turbine components listed in the response to Question 2.a. The turbine itself remains within the scope of the Maintenance Rule.

STPNOC will continue to comply with GDC-4 when the proposed change is implemented. The safety-related components that are potential targets for turbine missiles are either buried (ECW piping) or protected by safety-related structures (SDGs housed in the Diesel Generator building).

3. UFSAR Section 3.5.13 states that "I[T]he results of this evaluation was that the turbine missile generation probability (P 1 ) is less than 10- 4 per year..."
a. Provide the actual P 1 value.

From WCAP-14732, "Probabilistic Analysis of Reduction in Turbine Valve Test Frequency for Nuclear Plants with Westinghouse BB-296 Turbines with Steam Chests, Revision 1" June 1997, and Westinghouse Report STP Turbine Valve Test Frequency Extension to 3 Months: An Evaluation of the Applicability of WCAP-14732, Revision 1, to STP Units 1 and 2 (Letter Report ST-WN-NOC-01-000129, June 26, 2001), PI is 7.7E-07 per year for a monthly test interval.

b. The dominant contributor to P 1 is the destructive overspeed probability, which is a function of the testing frequency of turbine valves (stop, governor, reheat stop, and intercept). Provide an updated estimate of P 1 based on the maximum anticipated surveillance, maintenance, and monitoring intervals for all SSCs whose programs will be deleted from the UFSAR upon deletion of the turbine missile design basis.

From the Westinghouse letter report cited above, PI is 1.1E-06 for a 3-month test interval.

Note that STPNOC assumes the missile has been generated in the analysis performed for this application (i.e., PI = 1). Although PI is dependent on the inspection interval, the conditional core damage probability (CCDP) calculated for this evaluation does not depend on the inspection interval since PI is assumed to be 1. The results of the analysis are well below the R.G. 1.174 guidance.

STPNOC plans to extend the test interval incrementally while monitoring the performance of the valves. STPNOC's goal is to balance test frequency to assure high valve reliability against the potential for inadvertent closure of a valve during a test resulting in a turbine trip. STPNOC would not expect the test interval to exceed 12 months. This frequency will allow the station to test the valves sufficiently in NOC-AE-03001631 Page 4 advance of refueling outages to be able to incorporate any required maintenance into the refueling outage schedule.

c. Reconcile the updated P1 value in RAI #3.b with that based on the plant-specific failure data that the staff requested in RAI #1.c.

The event described previously has no effect on the turbine missile frequency estimate.

4. Section 4, "Technical Analysis," of the November 14, 2002, submittal, states that, "the probability of core damage, given that a turbine missile is generated, is 3.74E-8 for shear failure and 3.09E-08 for shear and rotational failure."
a. Provide the PRA document showing the detailed PRA analysis and results quoted above. The documentation should identify (i) all sequences and scenarios evaluated and (ii) all SSCs postulated to be failed by missile impacts in each scenario.

Please see the attached assessment (Attachment 2).

b. Please confirm that the evaluation done in support of the submittal included all SSCs that are credited in the PRA as potential targets of the turbine missiles and was not restricted to safety related SSCs as implied by the text in Section 4.

The evaluation focused on safety-related SSC's credited or analyzed in the PRA.

Non-safety-related SSC's credited in the PRA were not evaluated. The non-safety related SSC's credited in the PRA that could be potential targets of a turbine missile are:

1. The Balance of Plant diesel generator in either Unit which supplies one instrument air compressor and an air compressor cooling water pump in the Unit. The instrument air system in the PRA is only used for the alignment of outside air to the control room and electrical auxiliary building ventilation systems in the event of loss of chilled water. Failure of this diesel generator without a loss of offsite power has no effect in the PRA. Failure of this diesel generator in the PRA with a loss of offsite power is much less significant than the systems and trains modeled in the turbine missile assessment of Attachment 2.
2. The Technical Support Center Diesel Generator which supplies the positive displacement charging pump used to provide back-up to reactor coolant pump seal cooling. Failure of this diesel generator with no loss of offsite power has no effect in the PRA. Failure of this diesel generator with a loss of offsite power is much less significant than failure of the systems and trains modeled in the turbine missile assessment of Attachment 2.

. .....- NOC-AE-03001631 Page 5

3. Non-safety related dampers in the control room and electrical auxiliary building ventilation systems used to align outside air for cooling in the event of a loss of essential chilled water. Failure of these dampers without a corresponding loss of essential chilled water has no effect in the PRA. The turbine missile assessment of Attachment 2 does not list the essential chilled water system as a potential target of a missile.
4. Non-safety related electrical distribution switchgear and transformers used to direct power from offsite to Class 1E AC power systems ("off-site power").

Failure of one of the switchgear or transformers has little effect in the PRA because of the Class lE emergency diesel generators provided to each ESF bus. Failure of an individual Non Class 1E 13.8kV bus or 13.8kv/4.16kV ESF transformer is much less significant than failure of the systems/trains modeled in the turbine missile assessment of Attachment 2 (e.g., MEAB 1 target, loss of 1 electrical train).

c. Report and justify the risk-ranking of the turbines and related SSCs identified in the response to RAI #2 as equipment of low safety significance, based on the SSC safety categorization approved for your July 30, 1999, risk-informed exemption requests from special treatment requirements.

Some of the components associated with SSC's identified in the response to RAI #2 are NOT of low safety significance. The EHC Auto Stop Trip (AST) Solenoid valves, which are part of the electrical overspeed protection, are currently Medium in the Graded Quality Assurance (GQA) program. The turbine trip function is ranked Medium in GQA. The turbine governor and turbine stop valves are ranked Low, the reheat stop and reheat intercept valves are not modeled in the PRA.

The proposed changes will not affect the turbine trip design for STP. The categorization of the AST valves will not be affected by the proposed change.

STPNOC will continue to maintain these valves in accordance with their risk-significance. The treatment of the turbine overspeed protection components does not depend on their description in the UFSAR or TRM requirements.

5. Regulatory Guide 1.174 requires an estimate of the change in core damage frequency (CDF) and the change in large early release frequency (LERF) that could be expected if the proposed changes are implemented. Using your responses to RAI
  1. 3 (regarding the potential change in failure frequency) and RAI #2 (identifying all SSCs to which changes to the surveillance, maintenance and monitoring programs can be made) please estimate this change in CDF and LERF. This analysis should, for example, include the change in reliability in the turbine valves and overspeed devices based on the maximum anticipated surveillance, maintenance, and monitoring intervals.

Using the information provided above and in the PRA analysis attachment, the probability of a turbine missile is 1.1E-06 for a three month test interval. The conditional NOC-AE-03001631 Page 6 probability of core damage is 2.685E-07 for Unit 1 or 3.046E-07 for Unit 2 for shear failure and 2.685E-07 for Unit 1 or 2.981E-07 for Unit 2 for shear and rotational failure.

The estimated core damage frequency is then the initiating event frequency times the conditional core damage probability:

Unit 1 L.1E-06 * (2.685E-07 + 2.685E-07) = 5.91E-13 per year Unit 2 1.IE-06 * (3.046E-07 + 2.98 1E-07) = 6.63E-13 per year The change in core damage frequency is calculated by subtracting the turbine missile generator frequency using one month testing frequency, 7.7E-07, from the three month test interval missile generation frequency and multiplying by the conditional core damage probability from turbine missile, or:

Unit 1 (1.LE 7.7E-07) * (2.685E-07 + 2.685E-07) = 1.77E-13 per year Unit 2 (1.IE 7.7E-07) * (3.046E-07 + 2.981E-07) = 1.99E-13 per year With the exception of the turbine missile that penetrates the containment, the change in Large Early Release Frequency would be, in most instances, at least a factor of 20 below the change in core damage frequency. For the Medium LOCA induced by a missile into the containment, the CCDP is 5.95E-09. This would be an upper limit on a large release from this missile.

The current Core Damage Frequency for Revision 4 of the STP PRA is 9.08E-06 per year and the current Large Early Release Frequency is 5.37E-07 per year.

NOC-AE-03001631 ATTACHMENT 2 CONDITIONAL CORE DAMAGE PROBABILITY GIVEN A TURBINE MISSILE IS GENERATED NOC-AE-03001631 Page 1 Purpose and Scope The purpose of this study is to evaluate the probability of core damage given that the main turbine in either unit generates a missile. Testing of the turbine governor and intercept valves may generate unnecessary exposure to a turbine trip without a commensurate improvement in nuclear safety.

Background

The STP IPE (submitted in letter ST-HL-AE4193, dated August 28, 1992) defines the Turbine Missile Impact and Damage Frequency as follows:

The frequency, f, of unacceptable damage to a system due to a turbine missile is calculated from, f = f,

  • f2
  • f3 , where:

f, = annual frequency of missile generation f2 = conditional probability of a missile striking an essential system given that a turbine missile has been generated f3 = conditional probability of unacceptable damage to the system given that a missile strikes the system Given that a missile is generated, the conditional probability of unacceptable damage to an essential system is given by, CPdamage = f2 *f3 The conditional core damage frequency, CCDFc 0 nd, can be calculated using a RISKMAN model by setting the damaged system to guaranteed failure. The conditional probability of core damage, CPcoredamage, is then calculated from either of the following equations:

CPcore damage = CPdamage

  • CCDPinit CPcore damage = CPdamage
  • CCDFcOn/y,
  • AOT (hrs) / 8760 (hrs/yr); where:

AOT - Technical Specifications Allowed Outage Time for the failed system plus the time necessary to achieve stable hot or cold shutdown conditions.

The conditional core damage probability, CCDPinit, is given for initiating events in file: Initiators STP_1999.xls. The conditional probability of core damage, CPcore damage, given that a generated turbine missile results in an initiating event (e.g. Steam Line Break, MLOCA, Loss of ECW, Loss of EAB HVAC), is calculated from, CPcorc damage = CPdamage

  • CCDPinit NOC-AE-03001631 Page 2 Technical Analysis The probabilities of system damage due to generation of a turbine missile are given in Tables I and 2 below. The f2 and f3 data are taken from Tables 3.4.7-3 and 3.4.7-4 of the IPE. Damage probabilities are calculated based on the target.

Table 1. Turbine Missile Damage Probabilities, CP .,,, (Shear Failure)

Unit 1 Unit 2 Target if2 I l__ ____I_____t, 'If.

RCB I 1.430E-03 0.0118 1.687E-05 RCB 2 3.450E-04 0.0 0.0 DGB I 3.176E-04 0.1583 5.028E-05 1.615E-04 0.7850 1.268E-04 DGB 2 5.206E-04 0.5122 2.667E-04 3.176E-04 0.1583 5.028E-05 FHB I FHB2 MEAB I 2.155E-04 0.1206 2.599E-05 MEAB 2 1.900E-05 0.0 0.0 AFW Tank I 2.018E-04 0.8332 1.68 1E-04 AFW Tank 2 IVC I 4.072E-04 0.8178 3.330E-04 IVC 2 3.770E-05 0.1709 6.443E-06 ECW Intake Structure 1.350E-04 0.8089 1.092E-04 Table 2. Turbine Missile Damage Probabilities, CPd,.m,, (Shear and Rotation Failure)

Unit 1 Unit 2 Target i'f, C 1`_ _ _If._ 'f, RCB I 1.566E-03 0.0 0.0 RCB 2 3.779E-04 0.0 0.0 DGB I 5.288E-04 0.0 0.0 0.0 0.0 0.0 DGB 2 7.882E-04 0.3782 2.98 1E-04 5.288E-04 0.0 0.0 FHB I FHB2 2 _

MEAB I 2.534E-04 0.0073 1.850E-06 MEAB 2 2.340E-05 0.0 0.0 AFW Tank I 2.066E-04 0.7849 1.622E-04 AFV Tank 2 IVC I 4.502E-04 0.8207 3.695E-04 IVC 2 4.570E-05 0.1438 6.572E-06 ECW Intake Structure 1.422E-04 0.7197 1.023E-04 Note: Blanks are for those targets located either outside the low trajectory missile strike zone or shaded by other targets.

' South Texas Project IPE, Table 3.4.7-4 and 3.4.7-3 Given a turbine missile impact on one of the targets identified in Table 1 or Table 2, the following assumptions are used to develop a conditional probabililty of core damage.

1. A turbine missile striking the Reactor Containment Building (RCB 1 & 2) could be assumed to cause unacceptable damage to a Reactor Containment Fan Cooling train or to the reactor coolant piping systems resulting in a Medium LOCA or to the steam generator steam or feed lines.
2. A turbine missile striking the Diesel Generator Building (DGB 1 & 2) could be assumed to cause unacceptable damage to an Emergency Diesel Generator.

NOC-AE-03001631 Page 3

3. A turbine missile striking the Mechanical Electrical Auxiliary Building (MEAB 1 & 2) could be assumed to cause unacceptable damage to Class 1E Electrical Systems or EAB HVAC systems resulting in loss of a train of EAB HVAC or Class 1E electrical power.
4. A turbine missile striking the Auxiliary Feedwater Storage Tank (AFW Tank 1 & 2) could be assumed to cause unacceptable damage to the storage tank resulting in the unavailability of all four trains of Auxiliary Feedwater.
5. A turbine missile striking the Isolation Valve Cubicle (IVC 1 & 2) could be assumed to cause unacceptable damage to piping systems resulting in a Steam or Feed Line Break. The limiting event in terms of Conditional Core Damage Probability (CCDP) is the Steam Line Break Outside Containment with a value of 3.25SE-05.
6. A turbine missile striking the Essential Cooling Water Intake Structure (ECW Intake Structure) could be assumed to cause unacceptable damage to an Essential Cooling Water train.
7. It is not likely that a turbine missile would penetrate additional barriers, such as reinforced concrete walls or flooring and physical spacing, that separate safety trains in safety related structures. Therefore it is reasonable to assume that damage to safety related structures would be limited to a single safety train in the targeted structure.
8. Generation of a turbine missile causes a trip of the affected unit.

The core damage probabilities, CPcore damage, resulting from possible system damage given a turbine missile are given in Tables 3 and 4 below. Core damage probability is calculated as follows:

  • For initiating events, the CCDPinit from model STP_1999 is multiplied by the conditional probability of damage from a turbine missile, CPdamnage. The effect of support system initiators are included with the associated equipment failure CDF contribution. The CCDP for the turbine trip is included for each unit.
  • For equipment failures that are not initiating events caused by turbine missiles from the other Unit, the core damage frequency per year given the equipment failure, CDFond/yr is multiplied by the conditional probability of damage from a turbine missile, CPdcamage, and by the total time identified in the Technical Specifications to achieve stable conditions (AOT +

mode changes). This product is divided by 8760 hours0.101 days <br />2.433 hours <br />0.0145 weeks <br />0.00333 months <br /> per year to convert to the probability of damage, CPcore damage-Core damage probability, CPcore damage, is the sum of the two calculations. The data in Tables 3 and 4 are presented for missiles generated in either Unit 1 or Unit 2, and for damage in either Unit.

NOC-AE-03001631 Page 4 Table 3 Conditional Core Damage Probabilities, CP core danmge- Shear Failure Damage event CPdamage CCDPijt CDFcondlyr AOT(') CPcore damage l ~~~~~~~(hrs)/8760 l_____ _____ ___ _ (h rs/yr)

Unit I Missile, Unit 1 Effect Turbine Trip 1.00 2.678E-07 -- 2.678E-07 DGB 1, loss of I DG train, 5.028E-05 1.449E-06 l -- 7.283E-11 Turbine Trip l Total 2.679E-07 Unit 1 Missile, Unit 2 Effect DGB 2, loss of I DG train 2.667E-04 -- 4.085E-05 372/8760 4.625E-10 IVC 2, Steam line break") 6.443E-06 3.258E-05 -- 2.099E-10 Total 6.724E-10 Unit 2 Missile, Unit 2 Effect Turbine Trip 1.00 2.678E-07 2.678E-07 DGB 2, loss of I DG train, 5.028E-05 1.449E-06 7.283E-I I Turbine Trip ECW Intake Structure, loss of 1.092E-04 1.497E-06 1.635E-10 1 Unit 2, ECW train, Turbine Trip Total 2.680E-07 Unit 2 Missile, Unit 1 Effect RCB 1, loss of I RCFC train 1.687E-05 1.17 1E-05 204/8760 4.602E-12 RCB 1,MLOCA 1.687E-05 3.528E-04 -- 5.953E-09 RCB 1, SG steam or feed line 1.687E-05 3.079E-05 -- 5.195E-10 break DGB 1, loss of I DG train 1.268E-04 -- 4.085E-05 372/8760 2.199E-10 IVC 1, Steam line break"' 3.330E-04 3.258E-05 1.085E-08 MEAB 1, loss of 1 EAB train 2.599E-05 -3) 3.754E-04 204/8760 2.272E-10 MEAB 1, loss of 1 electrical 2.599E-05 -- 2.055E-04 44/8760 2.682E-1 1 train AFW Tank 1, loss of all AFW 1.681E-04 -- 6.045E-02 16/8760 1.857E-08 ECW Intake Structure, loss of 1.092E-04 ( 9.241E-05 204/8760 2.350E-10 1 Unit I ECW train Total 3.660E-08 (1) AOT includes the time to a stable plant condition as defined in the Technical Specifications (Cold shutdown or hot shutdown)

(2) Steam line break outside containment is limiting. SLBO CCDP - 3.258E-05; Feed Line Break Outside Containment CCDP - 3.4211E-07 (3) The effect of the support system initiator - Loss of EAB HVAC, Loss of ECW, and Loss of CCW are included in the CDF~.0 d/year presented.

NOC-AE-0300163 1 Page 5 Table 4 Conditional Core Damage Probabilities, CP cre danmge - Shear and Rotation Failure Damage event CPdamage CCDP1 11 w CCDFCOnd AOTt1 ' CPcore damage (hrs)/8760

__ __ _ _ _ __ _ _ _ _ __ __ __ __ __ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _(h -s/ yF r

Unit 1 Missile, Unit 1 Effect Turbine Trip 1.00 2.678E-07 -- -- 2.678E-07 Total 2.678E-07 Unit 1 Missile, Unit 2 Effect DGB 2, loss of 1 DG train 2.9811-04 4.0852-05 372/8760 5.1712-10 IVC 2, Steam line break(2) 6.572E-06 3.258E-05 - -- 2.141E-10 Total 7.3122-10 Unit 2 Missile, Unit 2 Effect Turbine Trip 1.00 2.678E-07 2.678E-07 EC2V Intake Structure, loss of 1.0232-04 1.497E-06 1.533E-10 I Unit 2 ECW train Total X 2.679E-07 Unit 2 Missile, Unit I Effect IVC 1, Steam line break-2 ' 3.695E-04 3.258E-05 -- 1.204E-08 MEAB 1, loss of I EAB train 1.8502-06 ( 3.754E-04 204/8760 1.617E-1 I MEAB 1, loss of 1 Electrical 1.850E-06 2.055E-04 44/8760 1.909E-12 train AFW Tank 1, loss of all AFW 1.622E-04 6.0452-02 16/8760 1.7912-08 ECW Intake Structure, loss of 1.023E-04 9.241E-05 204/8760 2.2022-10 1 Unit 1 ECW train Total 3.018E-08 (1) AOT includes the time to a stable plant condition as defined in the Technical Specifications (Cold shutdown or hot shutdown)

(2) Steam line break outside containment is limiting. SLBO CCDP - 3.258E-05; Feed Line Break Outside Containment CCDP - 3.421E-07 (3) The effect of the support system initiator - Loss of EAB HVAC, Loss of ECW, and Loss of CCW are included in the CDFcond/year presented.

NOC-AE-03001631 Page 6 Conclusions As seen in Tables 3 and 4, the risk to the units given a turbine missile event is dominated by the conditional probability of core damage associated with the resultant turbine trip, 2.68E-07. The risk in the other unit is dominated by the effects of Unit 2 missiles on Unit 1 equipment, primarily the auxiliary feedwater storage tank. This analysis does not consider the effects of a turbine missile on non-safety related equipment or the likelihood of the missile event itself.

Based on the this analysis, the risk of core damage associated with the proposed change given a turbine missile is generated is insignificant (<1E-06) and does not involve a significant increase in the probability of occurrence or the consequences of an accident or malfunction of equipment important to safety.

References:

1. South Texas Project Level 2 Probabilistic Safety Assessment Individual Plant Examination, Section 3.4.7.2, Turbine Missile Risk, 2/1992.
2. Initiators STP_1999.xls (attached)
3. STP PRA model STP_1999, October 25, 2001 Initiating event CCDPs From "Initiators STP_1999.xls" Initiator Description DE Freq. CDF CCDP LOEAB I Loss of EAB HVAC, BCRUN, UVAC A=F, HVAC C=F 7.746E-02 0 0 LOEAB2 Loss of EAB HVAC, BCRUN, HVAC A=F 2.4122E-04 1.080E-06 4.479E-03 LOEAB3 Loss of EAB HVAC, BCRUN, All Support 1.867E-06 1.583E-07 8.478E-02 LOECWI Loss of ECV, BCRUN. ECW A=F, ECW C=F 4.841 E-02 0 0 LOECW2 Loss of ECW, BCRUN, ECW A=F 1.767E-04 1.71 0E-08 9.676E-05 LOECW3 Loss of ECW, BCRUN, All Support 7.701 E-07 1.31 OE-09 1.701 E-03 LOCCWI Loss of CCW, BCRUN, CCW A=F, CCW C=F 1.136E-01 0 0 LOCCW2 Loss of CCW, BCRUNCCWA=F 1.104E-03 1.312E-09 1.188E-06 LOCCW3 Loss of CCW, BCRUN, All Support 2.097E-05 1.831 E-10 8.733E-06 MLOCA Medium LOCA 2.661 E-05 9.387E-09 3.528E-04 FLBO Feed line Break Outside Containment 3.363E-03 1.9009-09 3.241 E-07 SLBI Steam Line Break (SLB) Inside Containment 1.030E-03 3.171E-08 3.079E-05 SLBD SLB Outside Containment 1.009E-02 3.286E-07 3.258E-05
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