RBG-34-834, Application for Amend to License NPF-47,changing Tech Spec Surveillance Requirement 4.3.8.2.a Re Turbine Overspeed Protection to Allow Monthly Testing of High Pressure Turbine Control Valves in Lieu of Weekly Testing

Application for Amend to License NPF-47,changing Tech Spec Surveillance Requirement 4.3.8.2.a Re Turbine Overspeed Protection to Allow Monthly Testing of High Pressure Turbine Control Valves in Lieu of Weekly Testing

ML20084U818
Person / Time
Site:	River Bend
Issue date:	04/16/1991
From:	Odell W GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20084U820	List: ML20084U822 RBG-34-834, Application for Amend to License NPF-47,changing Tech Spec Surveillance Requirement 4.3.8.2.a Re Turbine Overspeed Protection to Allow Monthly Testing of High Pressure Turbine Control Valves in Lieu of Weekly Testing
References
RBG-34-834, NUDOCS 9104230008
Download: ML20084U818 (10)

Text

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G 7LF STA TCS U'TILITIES C OIVIE'JA NT/

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April 16, 1991 RBG- 34,034 File Nos. G9.5, G9.42 U. S. Nuclear Regulatccy Commission Document Control Desk Washington, D.C. 20555 Gentlement River Bend Station - Unit 1 Docket No. 50-458 Gulf States Utilities Company (GSU) hereby files an application to amend the River Bend Station - Unit 1 Technical Specifications, Appendix A to Facility Operating License NPF-47, pursuant to 10CFR50.90. This applination is filed to change Technical Specification Surveillance Requirement 4.3.8.2.a, " Turbine Overspeed Protection System," to allow monthly testing of the high pressure turbine control valves instead of weekly. The Attachment to this letter and the Enclosure provide the f etifications and proposed revisions to the Technical <pecifications, respectively.

Should you have any questions, please contact Mr. L. L. Dietrich of my staff at (504)381-4866.

Sincerely,.

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. H.'Odell

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Manager- Oversight h ,% River Bend Nuclear Group E/LLD/MSF Attachment e

9104230008 910416 PDR ADOCK 0500045,8

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' 'd cci U.S. Nuclear Regulatory Commission 1 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 NRC Resident Inspector P.O. Box 1051 St. Francisville, LA 70775 Claudia Abbate U.S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852 Mr. Glenn Miller Radiation Protection Division Louisiana Department of Environmental Quality Post-Office Box 14690 Baton Rouge, LA 70890 2

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UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION STATE OF LOUISIANA )

PARISit OF WEST FELICIANA )

Docket No. 50-458 In the Matter of )

GULF STATES UTILITIES COMPANY )

(River Bond Station - Unit 1)

AFFIDAVIT W. H. Odell, being duly sworn, states that he is Manager -

Oversight for Gulf States Utilities company; that he is authorized on the part of said company to sign and file with the Nuclear Regulatory Commission the documents attached hereto; and that all such documents are true and correct to the best of his knowledge, information and belief.

W. 11. 'Odell \

Subscribed and sworn to before me, a Notary Public in and for the State and Parish above named, this day of , 1991. My commission expires with Life.

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Ava C. Roach Notary Public in and for East Feliciana Parish, Louisiana authorized to act in West Feliciana l Parish, Louisiana

ATTAC1! MENT PROPOSED GULF STATE 8 UTILITIES COMPANY RIVER BEND STATION DOCKET 50-458/LICEH8E NO. NPF-47 TURBINE OVERSPEED PROTECTION SYSTEM (91-01)

LICENSING DOCUMENT INVOLVED: TECHNICAL SPECIFICATIONS ITEM: 4.3.8.2.a.3 REABON FOR REQUEST In accordance with 10CFR50.90, Gulf States Utilities Company is requesting a change to River Bend Station Technical Specification (TS) 4.3.8.2.a.3 to incorporate vendor recommendations to decrease the surveillance frequency for the testing of the four high pressure turbine control valves from weekly to monthly. General Electric (GE) Technical Information Letter (TIL) No. 969, dated May 22, 1984, and Service Information Letter (SIL) No. 413, dated October 4,1984, both recommend the reduced testing frequency. The current surveillance requirement has previously incorporated GEs recommendation of reduced testing frequencies for three out of four sets of turbine valvest the main stop valves, the intermediate stop valves and the intercept valves.

The operating experience accumulated on in-service nuclear units during the 24+ years prior to 1984, has shown considerably lower valve failure rates than those values upon which the original GE recommendations were based. These reduced f ailure rates are due to many design improvements to the nuclear turbino valves and controls that have been incorporated into the GE large steam turbine through GE's TILs and Engineering Change Notices (ECNs).

In General Electric's " Memo Report - Hypothetical Turbine Missiles

- Probability of Occurrence," dated March 14, 1973, the probability of runaway failure and' wheel burst of a GE nuclear turbine was given, based on the nuclear experience up to that time. Included in the probability calculations were the recommended valve test intervals (i.e., daily for main stop and intermediate stop and intercept valves, weekly for control valves) . The Nuclear Wheel Information Letter No. 2, dated November 8, 1982, gave comparative values for the increased overspeed probabilities due to increasing test intervals.

Based on past in-service experience with nuclear turbine steam valves, turbine steam inlet valve reliability and testing intervals are no longer the major contributing factors in determining hypothetical turbine missiles. The overall probability of a i

Page 1 of 5 l

l i hypothetical missile is therefore increased only a negligible

! amount by increasing the test interval of the valves. Incraasing test intervals will correspondingly decrease the probability of a system upset during such testing and should therefore increase the nuclear plant availability.

This change, if incorporated, would 1) greatly decrease unnecessary mechanical wear to the valves, 2) decrease the number of times that the turbine steam load-is not equally distributed, 3) increase capacity factor by not having to reduce reactor power to s 80% to perform this surveillance requirement weekly, and 4) increase capacity factor due to the time it takes to reach 100% Rated Thermal power after a xenon transient that is inherent with any power reduction and subsequent ascension.

This reduced surveillance frequency does not effect the Reactor protection System testing function.

Figure 1 provides a simplified drawing to show that the main steam flows from the four main steam lines into an equalizing header (to equalize main steam line flow), through the four Turbine Stop Valves (TSV), through the four Turbine Control Valves (TCV) and enters the center of the high pressure turbino casing. Each TCV regulates the steam flow to one of the four nozzle boxes, two in the upper half.shell and two in the lower half shell. The uniform flow distribution and the relatively thin walls of the nozzle boxes produce _ uniform heating of the shells to reduce distribution and minimize turbine shaft vibration. l The primary function of the control valves is to regulate reactor pressure and stop the steam flow to the high pressure turbine on a generator trip. They are located immediately downstream of the turbine:stop_ valves.

The control valves (Figure 2) are balanced piston valves, reducing the forces required to lift the valve disc. Each control valve is operated by a single acting spring-to-close servomotor. It is opened by a servo-valve.that receives its_ signal'from the_ Electro-

}lydraulic Control (EHC) System. This servomotor and servo-valve control arrangement comprises-_the power actuator of each valve.

DESCRIPTION:

The turbine overspeed protection system Technical _ Specification 3/4.3.8 is provided to ensure that the turbine overspeed protection system instrumentation and the turbine. speed control valves are operable and.will protect the turbine from excessive overspeed.

This is required since excessive overspeed of the turbine could generate potentially damaging missiles.

The_ surveillance requirements and frequencies reflect GE's recommendations which are based upon accumulated operating Page 2 of 5

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experience and are included in the Technical Specifications to demonstrate that the turbine overspeed protection system is operabic.

General Electric has presented to the NRC their methodology for examining turbine rotors with respect to calculating the probability of a failure which would generate missiles from the turbine. The NRC has approved this General Electric methodology (reference letter to GSU/Deddens from NRC/Paulson dated August 26, 1987). General Electric has employed these NRC approved methods to examine the River Bend Station turbine rotors and has determined the probability of turbine missile generator due to rotor failure.

As discussed in Section 3.5 of the RBS USAR, the overall probability of unacceptable damage occurring from Since turbineNUREG-0800, generated missiles to critical plant regions is 5.0 E-9.

Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants, and RG-1.115, Protection Against Low Trajectory Turbine Missiles, specify 1.0 E-7 as the maximut acceptable probability for turbine missile generated damage to safety related equipment, it is clear River Bend exceeds this criteria up to and beyond 6 years of turbine service. USAR Section 10.2 indicates the minimum LP rotor inspection interval at River Bend is 6 years. When the rotor is inspected at or before the 6 year scheduled inspection, a new missile generation probability report will be issued by General Electric and subsequent inspection intervals will be adjusted if indicated by the report. GSU has committed to follow GE's turbine system maintenance program which has been approved by the NRC, as outline in Supplement 5 of the River Bend Safety Evaluation Report.

GE has determined that, effective with TIL 969, the recommended valve test intervals for nuclear turbine control valves should be monthly.

)LO DISEHlgAN.1_lLMARDB con 8IDERATJRE1 As discussed in 10CFR50.92, the following discussions are provided to the NRC Staff in support of "no significant hazards considerations":

1. No significant increase in the probability or the consequences of an accident previously evaluated results from this change because:

The General Electric (GE) probabilistic analysis for the River Bend Station turbine has demonstrated that the probability of turbine failures are well within acceptable limits. This analysis has been previously reviewed and results approved by the NRC (reference letter to GSU/Deddens from NRC/Paulson, dated August 26, 1987).

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2. This change would not create the possibility of a new or different kind of accident from any accident previously evaluated because:

The change in surveillance frequencies does not create the possibility of a new or different kind of accident.

4 Additionally, the turbine control valve surveillance frequency has negligibic affect the GE missile probabilistic results.

3. This change would not involve a significant reduction in the

, margin of safety becauset ]

The GE probabilistic analysis demonstrates that the !

probability of unacceptable damage to plant safety-related  !

equipment due to potential turbine missile generation is considerably within the limits specified in NUREG-0800, section 2.2.3, and RG 1.115.

The proposed amendment will not increase the possibility or the consequences of a previously evaluated event and will not create a new or different kind of accident from any previously evaluated.

Also, the results of this proposed change are clearly within all acceptable criteria with respect to system components and design requirements. The ability to perform as described in the USAR is maintained and therefore, the proposed change does not involve a significant reduction in the margin of safety or significant hazards.-

REVISED TECHNICAL SPECIFICATIONt-The-requested revision is provided in the Enclosure.

SCHEDULE FOR ATTAINING COMPLIANCE:

GSU is currently in' compliance with the applicable Technical Specification requirements.

NOTIFICATION OF STATE PERSONNEL:

A copy of this amendment request has been provided to the State of Louisiana, Department of Environmental Quality -

Radiation Protection' Division.

' ENVIRONMENTAL IMPACT APPRAISALt

- GSU has reviewed the proposed license amendment against the criteria of 10CFR51.22 for environmental considerations. The proposed changes do not involve a significant hazards consideration, nor increase the types and amounts of effluents that may be released ~offsite, nor significantly increase individual or cumulative occupational radiation exposures. Based on the

' GSU' concludes that the proposed change meets the foregoing, Page 4 of 5

r criteria given in 10CFR51.22(c)(9) for a categorical exclusion from the requirement for an Environmental Impact statement.

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