ML17241A444
| ML17241A444 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 08/18/1999 |
| From: | Stall J FLORIDA POWER & LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML17241A445 | List: |
| References | |
| L-99-146, NUDOCS 9908300156 | |
| Download: ML17241A444 (21) | |
Text
St. Lucie Unit 2 Docket 50-389 Proposed License Amendment 8/1gygg ~
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ATTACHMENT1 to L-99-146 EVALUATIONOF PROPOSED LICENSE AMENDMENT 1.0 Introduction 2.0 Background and Discussion e 2.1 2.2 St. Lucie Turbine and Overspeed Protection System UFSAR References 2.3 WCAP-11525 2.4 Turbine Trip Failure 2.5 WCAP-'I 4732 2.6 NUREG-1366 .
3.0 Proposed License Amendment: Description and Basis 3.1 Description 3.2 Basis 3.2.1 Probabilistic Basis 3.2.2 WCAP-14732, Revision 1 3.2.3 WCAP-14732, Revision 1, Addendum 1 3.2.4 Evaluation of Turbine Missile Ejection Probability Resulting from Extending the Test Interval of Interceptor and Reheat-stop Valves at St. Lucie Units 1 and 2 4.0 Environmental Consideration 5.0 Conclusion
St. Lucie Unit 2 .L-99-146 Docket No..50-389 'Attachment 1 Proposed License Amendment Page1 of9 EVALUATIONOF PROPOSED LICENSE AMENDMENT 1.0 Introduction The proposed amendment to Facility Operating License NPF-16 for St. Lucie Unit 2 (PSL2) will change the required surveillance test frequency for cycling the steam valves in the turbine overspeed protection system from once per month to once per quarter (92 days). The test requirement is documented in the St. Lucie Unit 2 Updated Final Safety Analysis Report (UFSAR), Section 13.7.1.6.2, and the proposed change will increase the probability of occurrence of a malfunction of turbine overspeed protection equipment. Therefore, an extension of the test interval for the throttle valves, governor valves, reheat-stop valves, and interceptor valves can not be implemented without prior Commission approval, i.e., the change in test periodicity constitutes an unreviewed safety question as defined in 10 CFR 50.59, and as such, 10 CFR 50.59(c) requires the licensee to submit an application for license amendment pursuant to Part 50.90.
Following approval of the amendment, the UFSAR will be updated pursuant to 10 CFR 50.71(e).
The proposed amendment is based on a probabilistic assessment of the effect(s) of various overspeed protection test intervals on the turbine missile ejection frequency for St. Lucie Units 1 and 2. The assessment was performed by the Westinghouse Electric Company LLC, and demonstrates that the calculated turbine missile ejection probability (per year) is acceptable. The report of the Westinghouse study (WCAP-14732, Revision 1, Addendum 1; April, 1999) concludes that, " It is therefore prudent to conservatively interpret the missile ejection frequency results as supporting quarterly testing until reasonable failure rate data can be accumulated based on quarterly testing."
2.0 Back round/Discussion 2.1 St. Lucie Turbine and Overs eed Protection S stem: The St. Lucie Unit 2 turbine is a Westinghouse Electric Corporation BB-296 turbine with steam chests. It consists of one double-flow high pressure (HP) turbine in tandem with two double-flow low pressure (LP) turbines. The turbine is a tandem-compound, four-flow exhaust, -1800 rpm unit with 44 inch last row blades, and has moisture separation and reheat between the high pressure and the two low pressure elements. The ac-generator and brushless-type exciter are direct-connected to the turbine generator shaft.
The HP turbine has two steam chests. Each steam chest has two stop (throttle) valves for steam admission, and two control (governor) valves for steam egress to the turbine. The throttle and governor valves are of the plug-type. Each of the four HP turbine exhausts is routed through a moisture-separator-reheater (MSR) to the LP turbines. Two MSRs supply each LP turbine, and each MSR flow path has one reheat-stop and one reheat-intercept (interceptor) valve arranged in series. The reheat-stop and interceptor valves are of the butterfly type. All 16 of the turbine steam valves are hydraulically operated by the digital-electronic-hydraulic (DEH) control system.
Hydraulic pressure keeps these valves open and loss of hydraulic pressure results in valve closure. The failure of one valve to close in each steam-path will not prevent the shutdown of the turbine.
St. Lucie Unit 2 L-99-146 Docket No. 50-389 Attachment 1 Proposed License Amendment Page2of9 The PSL2 turbine is provided with two automatic overspeed trip systems (electro-hydraulic system and mechanical overspeed trip device) that have conservative trip settings of approximately 111%
of rated speed. The redundant systems have independent and diverse speed sensing devices.
When the overspeed trip setting is reached, each protection system operates to drain the high pressure hydraulic fluid from under the servo-actuator for each valve, which results in closure of all throttle, governor, reheat-stop, and reheat-intercept valves and isolation of the HP and LP turbine elements from their respective steam supplies. In addition, the overspeed protection controller is designed to limit a turbine overspeed condition in the event of a partial or complete loss of load and if the turbine reaches or exceeds 103% of rated speed, by modulating the governor and reheat-intercept valves. The system design is such that loss of hydraulic pressure or power failure in the electro-hydraulic system will trip the turbine and the reactor.
Because the function of the turbine valves is to control and limit the turbine speed and, in the case of loss of load, trip the turbine by stopping the supply of steam, regular testing and inspection of each valve reduce the probability of valve failure which, in turn, reduces the potential for turbine overspeed. A turbine overspeed condition increases the potential for turbine missile generation due to increased stress in the turbine rotor at higher operating speeds.
Therefore, the valve test interval can affect the estimated reliability of the overspeed protection system to perform its intended function upon demand, and, in turn, affects the probability of turbine overspeed and turbine failure missile ejection.
Turbine overspeed protection must be operable in Mode 1, and in Modes 2 and 3 if all steam paths to the turbine are not isolated. In those plant conditions, demonstration of operability must be performed at least once per month by cycling each of the 16 steam control and stop valves through at least one complete cycle from the running position, and by direct observation of each valve's movement through a complete cycle. In addition, a channel calibration must be performed on the turbine overspeed protection systems at least once per 18 months, and at least once per 40 months at least one throttle valve, governor valve, reheat-stop valve, and reheat-intercept valve must be disassembled to perform a visual and surface inspection of the valve seats, disks, and stems to verify no unacceptable flaws or corrosion.
2.2 UFSAR
References:
The turbine control and protective devices, including the overspeed protection system,-are described in-Subsections 7.7.1.1.10, '10.2.2.2, and 10.2.2.3 of the PSL2 UFSAR. A brief description of turbine rotor testing and inspection is provided in UFSAR Section 10.2.5. Operability and surveillance requirements for turbine overspeed protection are described in UFSAR Section 13.7.1.6. The licensing basis evaluation of turbine failure missiles is described in UFSAR Section 3.5.1.3. Approval of this proposed license amendment will authorize the appropriate revisions to the Unit 2 UFSAR that are necessary to implement an extension of the turbine overspeed protection system test interval from monthly to quarterly. The UFSAR would then be updated pursuant to 10 CFR 50.71(e).
It should be noted here that the initial PSL2 operability and surveillance requirements for turbine overspeed protection were issued as part of the original facility operating license (April 6, 1983),
and testing the system was required at least once per 7 days (formerly technical specification (TS) 3/4.3.4). The weekly test interval was extended to monthly by license amendment No. 4 (December 20, 1983). Subsequently, PSL2 license amendment No. 86 (August 20, 1996), in part, authorized re-location of the turbine overspeed protection specifications to the UFSAR. The re-location was accomplished without change to the specified requirements.
St. Lucie Unit 2 L-99-146 Docket No. 50-389 Attachment 1 Proposed License Amendment Page 3 of 9
2.3 WCAP-11525
The Westinghouse topical report, WCAP-11525, entitled "Probabilistic Evaluation of Reduction in Turbine Valve Test Frequency," June 1987, was developed in support of several owners of Westinghouse nuclear steam turbines and submitted to the NRC staff for review. The St. Lucie Plant units were included in this study. Consequently, the NRC staff documented the results of their review in a letter with an enclosed safety evaluation to FPL (Docket Nos. 50-335 and 50-389, Jan A. Norris (NRC) to W.F. Conway (FPL),
Subject:
St. Lucie Units 1 and 2 Staff's Assessment of WCAP-11525 Probabilistic Evaluation of Reduction in Turbine Valve Test Frequency; January 6, 1989).
The Staff concluded that WCAP-11525 is acceptable as a methodology reference, and that the topical report may be used to enable licensees to recalculate the missile ejection probabilities for their plants to account for significant changes in valve failures, control and trip system anomalies, turbine rotor inspection intervals, or any other factors which may affect the potential for overspeed or missile generation. However, it was determined that the failure data used to calculate the missile ejection probabilities in WCAP-11525 was not representative of St. Lucie Units 1 and 2 due to (then) recent experience with failure of valves similar to those found on the St. Lucie units, e.g., failures had been observed on other Building Block BB-296 turbines with steam chest, in which throttle valves failed to close on demand under test conditions. The staff's letter to FPL states, "Should you wish to use WCAP-11525 in support of your future submittais for licensing actions for the St. Lucie Plant, such submittals should be supported also by evidence that the plant failure data used in the subject report is representative of the St. Lucie Plant. Alternately, a reanalysis should be submitted. Such reanalysis may use the methodology of WCAP-11525" The failure rates for BB-296 steam chests were recalculated in 1988 and the resultant probabilities of turbine destructive overspeed were promulgated to the applicable operating plants by Westinghouse Operations and Maintenance Memo 093 (OMM-093, November, 1988). In addition, "Westinghouse Availability Improvement Bulletins" were issued to address turbine valve issues. FPL implemented the vendor recommended maintenance and improvement actions related to the applicable turbine valves.
2.4 Turbine Tri Failure: Failure of the turbine overspeed protection systems to trip the respective turbine as a result of mechanical failure of the throttle, governor, reheat-stop, or interceptor valves has not occurred at either St.-Lucie unit. However, an event did occur at PSL2 on April 21, 1992, wherein the turbine failed to trip on demands from both the automatic turbine-trip-by-reactor-trip feature and the control room manual turbine trip pushbuttons. The cause of the event was attributed to a malfunction of solenoid valve 20/AST, in conjunction with blockage of a hydraulic-fluid drain port by particulate matter in solenoid valve 20/ET. The mechanical and electrical overspeed trips were not challenged during the event, and shutdown was accomplished by operating the local trip-lever at the turbine front standard (Docket 50-389, LER 92-001 and LER 92-001, Revision 1, dated May 20 and June 29, 1992, respectively).
Additional details of the April 21, 1992 event and the associated failure analysis were also provided to the NRC staff by FPL letter L-92-149: D.A. Sager (FPL) to NRC (DCD), Docket 50-389, "Turbine Trip Failure Update," May 14, 1992. This PSL2 event, in addition to a system failure that had previously occurred in 1991 at another station, led to revisions to the 20/ET and 20/OPC solenoid valve models and failure rates that are used in the probabilistic analysis discussed in this submittal as WCAP-14732.
St. Lucie Unit 2 L-99-146 Docket No. 50-389 Attachment 1 Proposed License Amendment Page4of9
2.5 WCAP-14732
A more recent study that, in part, provides the basis for this proposed license amendment is described in the Westinghouse topical report WCAP-14732, Revision 1, which is entitled, "Probabilistic Analysis of Reduction in Turbine Valve Test Frequency for Nuclear Plants with Westinghouse BB-296 Turbines with Steam Chests," June 1997. The report contains the results of extending the test interval of turbine valves on the annual probability of turbine missile ejection due to destructive overspeed, using BB-296 turbine throttle and governor valve failure rates and system separation frequency. Turbine missile ejection probabilities (per year) for various valve test intervals ranging from 7 days to 12 months were calculated following the applied basic methodology described in the 1987 Westinghouse report WCAP-11525.
Although data collected and evaluated in this study included data from St. Lucie, e.g., the previously mentioned 1992 event, St. Lucie Units 1 and 2 were not specifically addressed in the WCAP-14732, Revision 1, results. As such, applicability of the report to St. Lucie needed to be evaluated on a plant-speciTic basis. In 1999, Addendum 1 to WCAP-14732, Revision 1, was issued to document the applicability of the recent BB-296 turbine study to St. Lucie Units 1 and 2.
2.6 NUREG-1366
To supplement the work performed by the NRC staff in support of the Technical Specifications Improvement Program (TSIP), the staff performed a comprehensive examination of all TS surveillance requirements in order to identify those that should be improved.
The results of that work are given in NUREG-1366, "Improvements to Technical Specifications Surveillance Requirements," published in December 1992. As previously discussed, turbine overspeed protection system requirements do not appear in the current St. Lucie TS; however, the following discussion remains applicable to an evaluation of the periodicity of turbine overspeed protection system testing.
Turbine overspeed protection system testing is identified in NUREG-1366 as a major source of reactor trips that occur during or as a result of on-line surveillance testing. The test is also a surveillance that results in some wear to the valves and stress to the steam system. In addition, because power is typically reduced to minimize the potential for a reactor trip during performance of the test, the unit capacity factor is impacted. However, NUREG-1366 cites a previous Westinghouse study (WCAP-11525) wherein it is stated, "[t]his type of testing is beneficial for (1) detecting non-or sluggish operation of the valves,. and (2) identification of gross outward appearance of valve condition." The staffs report then recognizes that "the test is beneficial in some ways and serves a safety function," and further states that, "The issue here is not whether the test should be done, but rather how often it should be done." (Ref: NUREG-1366, Sections 3.7, 3.10, and 5.13).
Section 5.13 of NUREG-1366 also states, "The NRC staff recommends that, where the turbine manufacturer agrees, the testing interval for turbine valves as part of the turbine overspeed protection system surveillances be extended from weekly and monthly tests to one test done quarterly, in which a direct visual observation will be made of the movement of each of the turbine valves currently required by Technical Specifications to be tested."
3.0 Pro osed Amendment: Descri tion and Basis 3.1 Descri tion: This proposed license amendment will revise the PSL2 license requirement currently specified in UFSAR Sections 13.7.1.6.2.a and b., as follows (the characters shown with
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l
St. Lucle Unit 2 L-99-146 Docket No. 50-389 Attachment 1 Proposed License Amendment Page 5of9 strike-through will be replaced by those shown in bold italics):
"The above required turbine overspeed protection system shall be demonstrated OPERABLE:"
- a. At least once per meath quarter by cycling each of the following valves through at least one complete cycle from the running position.
- 1. Four high pressure turbine stop valves.
- 2. Four high pressure turbine control valves.
- 3. Four low pressure turbine reheat stop valves.
- 4. Four low pressure turbine reheat intercept valves.
- b. At least once per 84 92 days by direct observation of the movement of each of the above valves through one complete cycle from the running position.
3.2 Basis Turbine overspeed protection is required since excessive overspeed of the turbine could generate potentially damaging missiles which, in turn, could impact and damage safety related components, equipment or structures. Although the design, manufacturing, and testing practices minimize the potential of a major turbine structural failure, such failures are hypothesized and either barriers or equipment separation is provided where indicated by analysis to protect Class I systems from turbine failure missiles. UFSAR Section 3.5.1.3 describes the St. Lucie Unit 2 licensing basis analysis performed to evaluate turbine generated missile hazards from an unfavorably oriented turbine, and classifies turbine failures into two general types referred to as design overspeed failures (120% of normal running speed) and destructive overspeed failures (194% of normal running speed). Risk probabilities were calculated for both low and high trajectory missiles associated with design and destructive overspeed. Based on this analysis in conjunction with a confirmatory, independent assessment of low trajectory missiles performed by the NRC staff, the calculated probabilities were found acceptable.
The staff's evaluation of turbine missile protection is documented in Section 3.5 of Supplement No. 1 to NUREG-0843, "Safety Evaluation Report related to the operation of St. Lucie Plant, Unit No. 2, Docket 50-389;" December 1981, and included review of the PSL2 overspeed protection system, inservice inspection program for the main steam stop and control valves and reheat valves, and data involving turbine disk integrity. The staff concluded that, " ... the total turbine missile risk from high and low trajectory missiles for the St. Lucie Unit 2 design is acceptably low so that the plant structure, systems, and components, important to safety are adequately protected against potential turbine missiles."
The PSL2 turbine is provided with redundant overspeed trip systems that have conservative trip settings of approximately 111% of rated speed. These systems have independent and diverse speed sensing devices, and actuate to close all throttle, governor, reheat-stop, and reheat-intercept valves (16 valves), which isolate the HP and LP turbine elements from their respective steam supplies. In addition, the overspeed protection controller is designed to limit a turbine overspeed condition in the event of a partial or complete loss of load and if the turbine reaches or exceeds 103% of rated speed, by modulating the governor and reheat-intercept valves. The system is also designed such that loss of hydraulic pressure or power failure due to any cause will
'k St. Lucie Unit 2 L-99-146 Docket No. 50-389 Attachment 1 Proposed License Amendment Page6of9 trip the turbine and the reactor.
FPL uses an "all volatile treatment" program for maintaining secondary water chemistry, which minimizes the buildup of foreign materials in the turbine steam valves. Based on plant operating experience, a turbine overspeed event as a result of mechanical failure of the stop and control valves or as a result of degraded performance of these valves has not occurred at PSL2.
Because of redundancy, failure of one of the stop or control valves to close in each steam-path will not prevent isolation of the HP and LP turbines from their respective steam supplies.
Pursuant to the PSL2 UFSAR, each turbine throttle, governor, reheat-stop, and reheat-intercept valve must be cycled from their running position at monthly intervals when the plant is in Mode 1, and in Modes 2 and 3 if all steam paths to the turbine are not isolated. Although this type of testing may be beneficial for detecting sluggish or non-operation of the valves, the test causes some wear to the valves and stress to the steam system, and represents a load threat for Mode 1 operation which could result in a significant reactor transient. NUREG-1366 discusses this test in the framework of "Improvements to Technical Specifications Surveillance Requirements," and recommends that, where the turbine manufacturer agrees, the testing interval for turbine valves as part of the turbine overspeed protection system surveillances be extended from weekly or monthly tests to one test done quarterly, in which a direct visual observation will be made of the movement of each turbine valve. The proposed change to UFSAR Section 13.7.1.6.2 will require the test to be performed at least once per quarter when the plant is in the applicable operating modes, and will continue to require direct observation of valve movement.
3.2.1 Probabilistic Basis: An evaluation of the impact from extending the test interval for the St.
Lucie Unit 1 and Unit 2 turbine valves from monthly to quarterly was performed by Westinghouse ~
Electric Company LLC. The probability of turbine missile generation (per year) as a function of various test intervals was examined for design (approximately 120% of rated turbine speed),
intermediate (approximately 130% of rated turbine speed), and destructive (runaway speed in excess of approximately 180%) overspeed events. The results of the evaluation are contained in three reports, which collectively form the basis for the proposed test interval:
(1) WCAP-14732, Revision 1, "Probabilistic Analysis of Reduction in Turbine Valve Test Frequency for Nuclear Plants with Westinghouse BB-296 Turbines with Steam Chests;"
Westinghouse Energy Systems, June 1997.
(2) WCAP-14732, Revision 1, Addendum 1, "Evaluation of the Applicability of WCAP-14732, Revision 1, to St. Lucie Units 1 and 2;" Westinghouse Electric Company LLC, April 1999.
(3) Letter Report, "Evaluation of Turbine Missile Ejection Probability Resulting From Extending the Test Interval of Interceptor and Reheat Stop Valves at St. Lucie Units 1 and 2;" prepared by Westinghouse Electric Company LLC, April 1999 (attachment to transmittal letter WOG-TVTFFPL-99-002 from A.P. Drake (Westinghouse Owners Group) to C. Buehrig (FPL), dated April 30, 1999).
i 1
St. Lucie Unit 2 L-99-146 Docket No. 50-389 Attachment 1 Proposed License Amendment Page 7 of 9 3.2.2 WCAP-14732 Revision 1: This report contains the results of extending the test interval of turbine valves on the annual probability of turbine missile ejection due to overspeed, using BB-296 turbine throttle and governor valve failure rates and system separation frequency. The turbine missile ejection frequencies for various valve test intervals were calculated following the applied basic methodology described in the 1987 Westinghouse report WCAP-11525, .
"Probabilistic Evaluation of Reduction in Turbine Valve Test Frequency," June 1987. WCAP-11525 is approved as an acceptable methodology reference for St. Lucie Units 1 and 2 by NRC letter: Docket 50-335 and 50-389, Jan A. Norris (NRC) to W.F. Conway (FPL),
Subject:
St. Lucie Units 1 and 2 - Staff's Assessment of WCAP-11525 - Probabilistic Evaluation of Reduction in Turbine Valve Test Frequency; January 6, 1989.
The missile ejection frequency results in WCAP-11525, for BB-296 steam chests, indicate that the design and intermediate overspeed failure probabilities are not major contributors to turbine missile ejection probability for plants with fully integral or heavy disc keyplate low pressure rotors.
Therefore, the study discussed in WCAP-14732, Revision 1, focuses on calculating the probability of destructive overspeed, and generic values are assumed for the probability of design and intermediate overspeed that are based upon the results for BB-296 steam chest models presented in WCAP-11525.
The failure rates used in WCAP-11525 for BB-296 steam chest valves were determined to be invalid as a result of incidents of sticking of governor and throttle valves in 1987 and 1988. The failure rates were subsequently re-calculated and the resultant probabilities of turbine destructive overspeed were distributed to all operating plants with BB-296 steam chests in Westinghouse
,Operations and Maintenance Memo 093 (OMM-093; November, 1988). FPL has implemented the vendor recommended maintenance and improvement actions related to the applicable turbine valves.
WCAP-14732, Revision 1, further revises the failure rates for BB-296 steam chest valves based on data collection for the period 1990-1995. This six-year period takes credit for improvements in design and maintenance while retaining adequate time for rare events to occur. The methodology for revising the failure rates is consistent with the methodology presented in WCAP-11525 and OMM-093. Revisions were also made to the 20/ET and 20/OPC solenoid valve models used in the fault trees. This, and the revised failure rates are based, in part, on a PSL2 event that occurred on April 21, 1992. The event is documented in Docket 50-389, LER 92-001 and LER 92-001, Revision 1, dated May 20 and June 29, 1992, respectively. It should also be noted that modifications to the St. Lucie turbine overspeed protection systems were made to prevent recurrence of that event.
Section 7 of WCAP-14732, Revision 1, states, in part, "The missile ejection frequencies shown in Figure 7-1 meet the acceptance criterion of 1.0E-5 per year for all test intervals analyzed. These results include conservative values for system separation frequency and the allowance for design and intermediate overspeed probabilities. The governor and throttle valve failure rates are based on plant operating experience (primarily monthly testing). Although extending the valve test interval is not expected to dramatically increase the valve failure rates, sufficient failure information at longer tests intervals do not currently exist. It is therefore prudent to conservatively interpret the missile ejection frequency results as supporting quarterly testing until reasonable failure rate data can be accumulated based on quarterly testing."
St. Lucle Unit 2 L-99-146 Docket No. 50-389 Attachment 1 Proposed License Amendment Page8of9 3.2.3 WCAP-14732 Revision 1 Addendum 1: WCAP-14732, Revision 1, presents the results of work performed by the Westinghouse Owner's Group (WQG) BB-296 Turbine Valve Test Frequency (TVTF) Mini Group to provide the probabilistic justification for extending the test intervals of the turbine governor valves and throttle valves. Addendum 1 to the report documents the applicability of the BB-296 mini group's work to FPL's St. Lucie Units 1 and 2, which joined the mini group after the issuance of WCAP-14732, Revision 1, and demonstrates that the results and conclusions of that report are applicable to the St. Lucie units. A separate study, described below, examined the missile ejection frequencies due to design and intermediate overspeed for various reheat-stop and interceptor valve test frequencies.
3.2.4 Evaluation of Turbine Missile E'ection Probabilit Resultin from Extendin the Test Interval of Interce tor and Reheat-sto Valves at St. Lucie Units 1 and 2: This part of the overall evaluation focused on two out of the three overspeed events previously defined that are affected by the failure probabilities of the reheat-stop valves and the interceptor valves, i.e., design overspeed (120% of normal running speed) and intermediate overspeed (132% of normal running speed). Destructive overspeed does not result from failures of the reheat-stop and interceptor valves.
The missile ejection probabilities due to design and intermediate overspeed were calculated using the latest BB-296 control (governor) valve failure data and generic data from both WCAP-11525 and WCAP-14732, Revision 1. Probabilities were calculated for reheat-stop valve and interceptor valve test intervals ranging from 3 to 18 months. However, the test interval of the control valve in the analysis is assumed to be quarterly based on the recommendations in Section 7 of WCAP-14732, Revision 1. Conditional probabilities are presented in the letter report (identiTied as report (3) in Section 3.2.1 above) that are based on LP turbine rotor inspection intervals of 5 years for the installed rotors in St. Lucie Units 1 and 2, and the spare rotors when they are installed in one of the units. The 5-year interval is consistent with the St. Lucie turbine rotor inspection program.
Page 3 of the report states, in part, "Table 3 shows that the missile ejection probabilities per year (P(T)), for design and intermediate overspeed for all three sets of rotors, are considerably less than 5% of 1.0E-5/yr (5.0E-07/yr) at all of the evaluated reheat stop valve and interceptor valve test intervals. -Therefore, the contribution of turbine missile ejection probability due to design and intermediate overspeed events remains a small fraction of the general acceptance criterion." The letter report also demonstrates that the allowance set for the design and intermediate overspeed missile ejection probabilities (generic) given in Section 4 of WCAP-14732, Revision 1, are valid and, therefore, the conclusions of that report remain valid for St. Lucie Units 1 and 2.
4.0 Environmental Consideration The proposed license amendment changes requirements with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20, and changes certain surveillance requirements. The proposed amendment involves no significant increase in the amounts and no significant change in the types of any effluents that may be released offsite, and no significant increase in individual or cumulative occupational radiation exposure. FPL has concluded that the proposed amendment involves no significant hazards consideration, and meets the criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9) and that, pursuant to 10 CFR 51.22(b), an
St. Lucie Unit 2 L-99-146 Docket No. 50-389 Attachment 1 Proposed License Amendment Page 9of9 environmental impact statement or environmental assessment need not be prepared in connection with issuance of the amendment.
5.0 Conclusion Appropriate barriers and separation exist such that the total turbine missile risk to plant structures, systems, and components important to safety remain adequately protected from turbine generated missiles, and the requirements of General Design Criterion 4 (environmental and dynamic effects design bases) are maintained. The proposed surveillance interval for the turbine overspeed protection system steam valves is adequate to ensure that the intent and design basis function for turbine overspeed protection remain satisfied. The analysis performed to support the proposed license amendment is based on acceptable analytical methods, and uses component failure data that is representative of the St. Lucie Units 1 and 2 turbine generator systems. The evaluation demonstrates that the impact on turbine missile generation frequency from extending the valve test interval is acceptable, and establishes the probabilistic basis for quarterly testing of the turbine valves. Following approval of the proposed amendment, the UFSAR will be updated pursuant to 10 CFR 50.71(e).
St. Lucie Unit 2 Docket No. 50-389 Proposed License Amendment ATTACHMENT2 to L-99-146 DETERMINATIONOF NO SIGNIFICANT HAZARDS CONSIDERATION
St. Lucie Unit 2 L-99-146 Docket No. 50-389 Attachment 2 Proposed License Amendment Page 1 of 2 DETERMINATIONOF NO SIGNIFICANT HAZARDS CONSIDERATION Descriptio of amendment request: The proposed amendment will change the required surveillance interval for cycling the steam valves in the turbine overspeed protection system from monthly to quarterly. The license requirement is documented in the St. Lucie Unit 2 Updated Final Safety Analysis Report Section 13.7.1.6.2, and the proposed change does not satisfy the 10 CFR 50.59 standards for a change that can be made by the licensee without prior Commission approval.
Pursuant to 10CFR50.92, a determination may be made that a proposed license amendment involves no significant hazards consideration if operation of the facility in accordance with the proposed amendment would not: (1) involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) involve a significant reduction in a margin of safety. Each standard is discussed as follows:
(1) Operation of the facility in accordance with the proposed amendment would not involve a significant increase in the probability or consequences of an accident previously evaluated.
The small increase in turbine missile ejection frequency resulting from extending the test interval for turbine valves is acceptable with respect to the NRC probabilistic acceptance criterion and supports quarterly testing. In addition, there are no physical changes to plant equipment or changes in plant operation that could initiate or adversely affect the mitigation or consequences of an accident previously evaluated. Turbine disk integrity remains unchanged since the turbine rotor inspection cycle is not affected by the change in valve testing frequency. Further, there are no changes to protective barriers or changes in separation of equipment important to safety. Therefore, safety related structures, systems, and components remain adequately protected against potential turbine missiles and the potential for turbine missile generation has not significantly increased. The change to extend the turbine valve test interval maintains the intent and design basis function being veriTied by the surveillance requirement. Therefore, operation of the facility in accordance with the proposed amendment will not involve a significant increase in the probability or consequences of an accident previously evaluated.
(2) Operation of the facility in accordance with the proposed amendment would not create the possibility of a new or different kind of accident from any accident previously evaluated.
There are no physical changes to plant equipment or changes in plant operation that could create a new or different kind of accident. This proposed change does not result in any plant configuration changes or create new failure modes. The small increase in turbine missile ejection frequency resulting from extending the test interval for turbine valves is acceptable with respect to the NRC probabilistic acceptance criterion and supports quarterly testing. New types of turbine missiles or strike probabilities are not created by extending the turbine valve test interval. No new or different kind of accident is created. In addition, turbine disk integrity
St. Lucie Unit 2 L-99-146 Docket No. 50-389 Attachment 2 Proposed License Amendment Page 2 of 2 remains unchanged since the turbine rotor inspection cycle is not affected by the change in valve testing frequency. Further, there are no changes to protective barriers or changes in the separation of equipment important to safety. Safety related structures, systems, and components remain adequately protected against potential turbine missiles, the potential for turbine missile generation has not significantly increased, and new or different kinds of accidents are not created. Therefore, operation of the facility in accordance with the proposed amendment would not create the possibility of a new or different kind of accident from any accident previously evaluated.
(3) Operation of the facility in accordance with the proposed amendment would not involve a significant reduction in a margin of safety.
This proposed surveillance change extends the turbine overspeed protection system turbine valve test frequency from monthly to quarterly. The results of turbine missile ejection frequency remain within NRC acceptance criterion and therefore supports quarterly testing.
There are no physical changes to plant equipment or changes in plant operation that involve a significant reduction in the margin of safety. Turbine disk integrity remains unchanged since the turbine rotor inspection cycle is not affected by the change in valve testing frequency.
There are no changes to protective barriers or changes in separation of equipment important to safety. Therefore, safety related structures, systems, and components remain adequately protected against potential turbine missiles and the potential for turbine missile generation has not significantly incr'eased. The change in turbine valve test interval maintains the intent and design basis function being verified by the surveillance requirement. As such, the assumptions and conclusions of the accident analyses in the UFSAR remain valid and associated safety limits will continue to be met. Therefore, operation of the facility in accordance with the proposed amendment would not involve a significant reduction in a margin of safety.
Based on the discussion presented above and on the supporting Evaluation of Proposed License Amendment, FPL has concluded that this proposed license amendment involves no significant hazards consideration.
St. Lucie Unit 2 't 0"CFR'2;790]NFQRMATlON Docket No. 50-389 Proposed License Amendment EXEMPT FROM DlSGLOSURE ENCLOSURE TO FPL LETTER L-99-146 Docket 50-389 This enclosure contains the following documents:
(1) One copy of the Westinghouse "Copyright Notice," not dated.
(2) One copy of the Westinghouse "Proprietary Information Notice," not dated.
(3) One copy of Westinghouse Electric Company letter, H.A. Sepp to Mr. Samuel J. Collins (NRC), APPLICATION FOR WITHHOLDING PROPRIETARY INFORMATION FROM PUBLIC DISCLOSURE, with accompanying affidavit: CAW-99-1350, August 11, 1999 (total 7 pages)
(4) One copy of transmittal letter WOG-TVTFFPL-99-002 (Non-proprietary) from A.P.
Drake (Westinghouse Owners Group) to C. Buehiig (FPL), dated April 30, 1999, with attached Letter Report (Proprietary), "Evaluation of Turbine Missile Ejection Probability Resulting From Extending the Test Interval of Interceptor and Reheat Stop Valves at St. Lucie Units 1 and 2;"
Westinghouse Electric Company LLC, April 1999 (total 10 pages)
(5) 'ne copy of Westinghouse Electric Company letter, John S. Galembush to Mr. Samuel J. Collins (NRC), APPLICATION FOR WITHHOLDING PROPRIETARY INFORMATION FROM PUBLIC DISCLOSURE, with accompanying affidavit: CAW-99-1347, July 22, 1999 (total 7 pages).
(6) One copy of WCAP-14732, Revision 1, Addendum 1 (Proprietary), "Evaluation of the Applicability of WCAP-14732, Revision 1, to St. Lucie Units 1 and 2;" Westinghouse Electric Company LLC, April 1999.
(7) One copy of WCAP-14732, Revision 1 (Proprietary), "Probabilistic Analysis of Reduction in Turbine Valve Test Frequency for Nuclear Plants with Westinghouse BB-296 Turbines with Steam Chests;" Westinghouse Energy Systems, June 1997.
As items (4), (6), and (7) above contain information proprietary to the Westinghouse Electric Company, they are supported by two affidavits (items (3) and (5)) signed by Westinghouse, the owner of the information. Each affidavit sets forth the basis on which the information may be withheld from public disclosure by the Commission and addresses with specificity the considerations listed in paragraph (b)(4) of Section 2.790 of the Commission's regulations.
Accordingly, it is respectively requested that the information which is proprietary be withheld from public disclosure in accordance with 10 CFR Section 2.790 of the Commission's regulations.
Correspondence with respect to the copyright or proprietary aspects of the items listed above or the supporting Westinghouse Affidavits should reference CAW-99-1347 or CAW-99-1350, as appropriate, and should be addressed to the Manager, Regulatory and Licensing Engineering, Westinghouse Electric Company, P.O. Box 355, Pittsburgh, PA 15230-0355.
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Copyright Notice The reports transmitted herewith each bear a Westinghouse copyright notice. The NRC is permitted to make the number of copies of the information contained in these reports which are necessary for its internal use in connection with generic and plant-specific reviews and approvals as well as the issuance, denial, amendment, transfer, renewal, modification, suspension, revocation, or violation of a license, permit, order, or regulation subject to the requirements of 10 CFR 2.790 regarding restrictions on public disclosure to the extent such information has been identified as proprietary by Westinghouse, copyright protection notwithstanding. With respect to the non-proprietary versions of these reports, the NRC is permitted to make the number of copies beyond those necessary for its internal use which are necessary in order to have one copy available for public viewing in the appropriate docket files in the public document room in Washington, DC and in local public document rooms as may be required by NRC regulations ifthe number of copies submitted is insufficient for this purpose. All copies made by the NRC must include the copyright notice in all instances and the proprietary notice ifthe original was identified as proprietary.
Proprietary Information Notice Transmitted herewith are proprietary and/or non-proprietary versions of documents furnished to the NRC in connection with requests for generic and/or plant-specific review and approval.
In order to conform to the requirements of 10 CFR 2.790 of the Commission's regulations concerning the protection of proprietary information so submitted to the NRC, the information which is proprietary in the proprietary versions is contained within brackets, and where the proprietary information has been deleted in the non-proprietary versions, only the brackets remain (the information that was contained within the brackets in the proprietary versions having been deleted). The justification for claiming the information so designated as proprietary is indicated in both versions by means of lower case letters (a) through (f) contained within parentheses located as a superscript immediately following the brackets enclosing each item of information being identified as proprietary or in the margin opposite such information. These lower case letters refer to the types of information Westinghouse customarily holds in confidence identified in Sections (4)(ii)(a) through (4)(ii)(f) of the affidavit accompanying this transmittal pursuant to 10 CFR 2.790(b)(1).