ML20202C562

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Application for Amends to Licenses NPF-4 & NPF-7,modifying Insp Requirements & Frequency for RCP Flywheels & Eliminating Insp Requirements for Unit 1,reactor Coolant Flow Straighteners
ML20202C562
Person / Time
Site: North Anna  Dominion icon.png
Issue date: 02/03/1998
From: Ohanlon J
VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20202C567 List:
References
98-066, 98-66, NUDOCS 9802120279
Download: ML20202C562 (11)
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Text

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VIRGINIA ELECTHIC AND POWER COMI%NY It tcunown,V HOIN!A 20261 February 3, 1998 U.S. Nuclear Regulatory Commission Serial No.98-066 Attention: Document Control Desk NL&OS/GSS/ETS R0 Washington, D.C. 20555 Docket Nos. 50 338 50 339 Licese Nos. NPF-4 NPF-7 Gentlemen:

VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 6CIFICATION CHANGE REACTOR COOLANT PUMP FLYWHEEL INSPECTIONS AND LOOP FLOW STRAIGHTENER INSPECTIONS Pursuant to 10 CFR 50.90, Virginia Electric and Power Company requests amendments, in the form of changes to the Technical Specifications and to Facility Operating License Numbers NPF-4 and NPF-7 for North Anna Power Station Units 1 and 2, respectively. The proposed changes will modify the inspection requirements and frequency for the Reactor Coolant Pump flywheels and eliminate the inspection requirements for the Unit 1 reactor coolant flow straighteners. A discussion of the proposed Technical Specifications changes is provided in Attachment 1.

The proposed Technical Specifications changes have been reviewed and approved by the Station Nuclear Safety and Operating Commit'ee and the Management Safety Review Committee. It has been determined that the proposed Technical Specifications changes do not involve an unreviewed safety question as defined in 10 CFR 50.59 or create a significant hazards consideration as defined in 10 CFR 50.92. The propesad Technical Specifications changes are provided in Attachment 2. The basis for our determination that the changes do not involve a significant hazards consideration is provided in Attachment 3.

In order to implement these revised augmented intoection requirements for the Reactor Coolant Pump motor flywheel inspections during the upcoming Unit 1 Fall 1998 refueling outage and subsequent refueling outages, and to reduce personnel radiation exposure, we request NRC review and approval of the requested changes by August 1, 1998.

9002120279 980203 8 DR ADOCK 0500

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' I If you have an,y further questions, please contact us.

Very truly yours, 1

James P, O'Hanlon -

Senior Vice President ' Nuclear

' Attachments

1.  : Discussion of Changes
2. Proposed Technical Specification Changes l l l 3. Significant Hazards Consideration Determination .

Commitments made in this letter:

4

1. There are no commitments in this letter cc: U.S. Nuclear Regulatory Commission Region ll Atlanta Federal Center

- 61 Forsyth Street, SW

' Suite 23T85

= Atlanta, Georgia 30303 Mr. M. J. Morgan

. NRC Senior Resident inspector North Anna Power Station Commissioner Department of Radiological Health Room 104A 1500 East Main Street Richmond, VA 23219

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) ; -

. COMMONWEALTH OF VIRGINIA-_  :-);

);

C ')UNTY_OF.HENRICO  :;)c fn-The foregoing document was acknow! edged before me, in and for. the County and Commonwealth aforesaid, today by -J. P. O'Hanlon,-_who is. Senior:Vice - .

President - Nuclear, of Virginia Electric and Power Company He has affirmed -

before me that he is duly authorized _to execute and file the foregoing document =

In behalf of that Company, and that the statements in the document are true to -

. the best of his knowledge and belief. _

Acknowledged before me this b day of l 71LidALI/','19b .7 My Commission Expires:: March 31,2000 -

}- Notary Public

[(SEAL)

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ATTACHMENT 1

+ L amt DISCUSSION OF CHANGES VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA UNITS 1 AND 2

Q Discussion of Change Inttoduallon Pursuant to 10 C; R 50.90, Virginia Electric and Power Company requests changes to Technical Specifications 3/4.4.10,

1. The current Surveillance Requirements require the flywheels to be inspected in accordanec with Pegulatory Position C.4.b of Regulatory Guide 1.14 and that the flow straighteners to be ultrasonically examined.

Tho proposed changes will replace the augmented inspection requirements for the leactor Coolant Pump flywheels specified by Regulatory Guide 1.14,

  • Reactor Coolant Pump Flywheel Integrity" Revisica 1 dated August 1975 with those established by WCAP 14535A, " Topical Report on P : tor Coolant Pump Flywheel Inspect!on Elimination" da'ed November 1996, and will eliminate the inspection requirements for the flow straighteners.

An unreviewed safety question or significant hazards consideration in not generated by the proposed Technical Specifications changes. Changes of the inspecuon requirements for the reactor coolant pump flywheels are based upon the results of Westinghouan Energy Systems Topical Report WCAP 14535A. The Topical Report was initiated to demonstrate that flywheel inspections could be eliminated without impairing plant safety. The results of Topical Report WCAP 14535A have been reviewed, evaluated, and accepted for referencing in license applications by the NRC in their letter entitled

  • Acceptance for Referencing of Topical Report WCAP-14535, Topical' Report on Reector Coolant Pump Flywheel inspection Elimination" dated September 12,1996.

Based upon the results of a visual inspection of the stub ends and an analysis of possible mechanisms of corrosion which could act upon the remaining splitter plate stub ends, it was concluded in 1982 that it was safe to operate Unit 1 with the splitter plates y rernoved and the stub ends in their present configuration. As confirmation of this conclusion, NAPS committed to and performed UT inspections in the region of the stub ,

ends at the number 5,6,7, and 8 Unit 1 refueling outages. However, the current Technical Specification augmented inspection requirements for the flow straighteners should have been eliminated upon the removal of the flow straighteners and the completion of the required stub end examinations. Thus, the elimination of the inspection requirements for the flow straighteners are based upon their removal in 1982 7 and the ccmpletion of subsequent examinations of the stub ends as committed to in previous correspondence to the NRC.

Page 1 of 7

1. '

Backg'ounc(*

r Current Licensing Basis General Design Criterion 4,

  • Environmental and dynamic effects design bases" of Appendix A,
  • General Design Critoria for Nuclear Power Plants" to 10 CFR 50 requires that nuclear plant structures, systems, and components important to safety be protectoo against the effects of missiles that might result from equipmont failures.

Regulatory Guide 1.14 describes a method acceptable to the NRC staff for implementing this requirement with regard to minimizing the potential for failures of reactor coolant pump motor flywheels.

Design Basis The reactor coolant pumps locater' in each loop provide the motive force to circulate the reactor coolant throughout the Reactor Coolant System. The reactor coolant pumps are vertical shaft, single suction, single stage, contrifugal pumps designed to move 94,667 gpm of reactor coolant through each loop. The RCP flywheel is located cbove the motor upper bearing and provides the RCP an extended flow coastdown capability during accidents which involve a loss of forced circulation. The stored kinetic energy / momentum of the flywheel provides the flow coas:down at an adequate rate to ensure core cooling.

Each RCP flywheel consists of two thick plates bolted together fabricated from vacuum d0 gassed A 533 Grade B Class I steel. It was determined during the initial design that the flywheel plate material was suitable for use and met the acceptance criteria specified in Regulatory Guide 1.14.

OltralaDion Flywheelinspection Reactor coolant pump motor flywheels have been subjected to an augmented inspection program that satisfies the requirements of Regulatory Position C 4.b of Regulatory Guide 1.14, Revision 1

  • Reactor Coolant Pump Flywheel Integrity" since 1979. Regulatory Guide 1.14, prepared in response to a concem over overspeed of the RCP and its potential for failure, describes an acceptable method to ensure RCP flywheel integrity. These inspections include an in place volumetric ultrasonic (UT) examination of the areas of higher stress concentration at the bore and keyway every 3 years, and a surface examination of all exposed surfaces and complete UT volumetric examination overy 10 years.

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Operating power plants have inspected their reactor coolant pump flywheei. for over 20 years with no' flaws identified that affect flywheel integrity. This inspection record, plus the concems over Inspection costs and personnel radiation exposure prompted Westinghouse Energy Systems to prepare WCAP 14535A to demonstrate through fracture mechanics analysis that flywheel inspections can be climinated without impairing plant safety. Therefore, West!nghouse Energy Systems prepared report WCAP 14535A, " Topical Report on Reactor Coolant Pump Flywheel Inspection Elimination" to quantify the effects of eliminating flywhool inspections, and it was reviewed and evaluated with the technical basis approved by the NRC.

WCAP 14535A which applies to the flywheels manufactured by Westinghouse provides the technical basis for climinating the augmented inspection of the reactor coolant pump flywheels. The topical report reviewed previous ISI results, provided a stress analysis and fracture mechanics evaluation of the flywheels, and assessed the risk -

significance of conducting the inspections. The conclusions are summarized below:

1. The material specification for the North Anna reactor coolant pump flywheels is SA 533 Grade B
2. Flywheel inspections have been performed for 20 years with no indications of service induced flaws
3. Flywheels exhibit a very high flaw tolerance based upon flywheel imegrity evaluations
4. Crack extension over a 60 year service life is negligible based upon failure probability evaluations
5. Eliminating inspecdon after 10 years of plant life will not change the probability of failure based on structural reliability studies
6. Inspections result in man rem exposure and the potential for flywheel damage during disassembly and reassembly Based upon these conclusions, Westinghouse recommended that continued inspections of reactor coolant pump flywheels could be eliminated without any significant change in risk. Although accepting the technical arguments presented in the report, the NRC only granted partial relief from the RCP motor flywheel inspection requirements.

The proposed Technical Specification changes implement the NRC recommended Inspection criteria as specified in the conclusion of NRC Letter, " Acceptance for Referencing of Topical Report WCAP-14535, ' Topical Report on Reactor Coolant Pump Flywheel Inspection Elimination' dated September 12, 1996" as supplemented by Safety Evaluation Report, " Safety Evaluation by the Office of Nuclear Reactor Regulation, Topical Report on Reactor Coolant Pump Flywheel Inspection Page 3 of 7

Examloation " Based upon the NRC recommended critoria, the proposed changes will requiro an inspection once every 10 years by a qualified in place UT oxamination over the volume from the inner bore of the flywhool to the circle of one half tbs outor radius or a surface examination (MT and/or PT) of exposed surfaces defined by the volumo of the disassembled flywhools, implomontation of these inspection requirements will also addross the concem of protecting against events or degradatlun that are not ant cipated and have not been considorod in the generic analysis.

This inspection approach is consistent with the requirements in the ASME Codo for successive inspections for flaws ovaluated to 1ho Soction XI acceptance critoria.

Furthermore, overall plant safety could be increased by reducing the frequency of these inspections due to the elimination of potential flywheel damage during disassembly and )

reassembly for inspection.

1 Flow Straightener Inspection Flow splitter plates (flow straighteners), which are not structural members, were installed in the reactor coolant loops to enhance flow distribution at the pump impellor ,

Inlet at .I to increase uniformity in velocity distribution. On March 21,1979, the NRC {

was notified that during a routino cleaning of the reactor coolant loop crossover leg '

pipos in Unit 2 cracks were discovered in the splitter plate installed in the RCS pipe elbow leading into the suction side of the RCP. Therefore, the flow splitter plates for Unit 2 woro removed prior to plant operation.

Since the Unit 1 elbows were of the same design, the flow splitter plates were ultrasonically examined in February,1981 whereby several indications were detected.

At that timo, the indications were acknowledged by the NRC and it was concluded that the indications did not represent a safety conccm. During the 1982 outage for Unit 1, the results of an augmented UT examination disclosed that the indications in all the flow splitters except one had grown significantly since the last outage. Therefore, in August and September of 1982, the flow splitter plates were removed from Unit 1 and a baseline UT examination was performed on the remaining stub ends.

Based upon the results of a visual inspection of the stub ends and an analysis of possible mechanisms of corrosion which could act upon the remaining splitter plate stub ends, it was concluded that it was safe to operate Unit 1 with the splitter plates removed and the stub ends in their present configuration. As confirmation of this conclusion, NAPS committed to perform UT inspections in the agion of the stub ends at the number 5,6,7, and 8 Unit refueling outages. These stub ends were ultrasonically examined during these next four rafueling outages as required by NRC Safety Evaluation Report transmitted to Virginia Electric and Power Company on December 6, 1982.

The augmented inspection requirements for the flow straighteners are being removed from Technical Specifications to eliminate a potential compliance concom. Therefore, Page 4 of 7

these changes will eliminate the Technical Specifications augmented inspection requirements for the flow straighteners removed in 1902.

Specific Channen Delete the following current Surveillance Requirement 4.4.10.1.1 for Units 1 and 2 and -

replace with following:

Current Unit 1 Surveillance Requirement 4.4.10.1.1 4.4.10.1.1 in addition to the requirements of Specification 4.0.5,1) the Reactor Coolant pump flywheels shall be inspected per the recommendations of Regulatory Position C.4.b of Regulatory Guide 1.14, Revision 1. August 1975 and 2) the flow straighteners in each steam generator to RCP elbow shall be W.isonically examined whenever a RCP shaft deflection of greater than 20 mils is indicated and at least once per 18 months."

Change to:

"4.4.10.1.1 In addition to the requirements of Specification 4.0.5, the Reactor Coolant pump flywheels shall be inspected once every 10 years by a quellflod in-place UT examination over the volume from the inner bore of the flywheel to the circle of one-half the outer radius or a surface examination (MT and/or PT) of exposed surfaces defined by the volume of the disassembled flywheels.'.'

Current Unit 2 Surveillance Requirement 4.4.10.1.1 "4.4.10.1.1 In addition to the requirements of Specification 4.0.5, the Reactor Coolant pump flywheels shall be inspected per the recommendations of Regulatory Position C.4.b of Regulatory Guide 1.14, Revision 1, August 1975."

Change to:

"4.4.10.1.1 in addition to the requirements of Specification 4.0.5, the Reactor Coolant pump flywheels shall be inspected once every 10 years by a quellfled in-place UT examination over the volume from the inner bore of the flywheel to the

- circle of one-half the outer radius or a surface examination (MT.and/or PT) of exposed surfaces defined by the volume of the disassembled flywheels."

Safety Slanificance The proposed Technical Specification changes for the reduction in inspection requirements for the reactor coolant pump flywheels, generically approved by the NRC and supported by WCAP 14535A,' and the elimination of the inspection requirements Page 5 of 7

t .

for the flow straigleteners do not affect the design or operation of the plant. The changes also'do not involve any physical modification to the plant or result in a change in a rnethod of system operation.

The postulated failure consequence frorn reducing the inspection requirements is the undetected inillation of a crack in a flywheel growing to the point of flywheel failure before subsequent examination. WCAP 14535A determined that discontinuing the flywheel examinations after the first 10 years of operation had essentially no impact on the failure probability. Tu tMs for this conclusion is that most critically sized flaws which can lead to failure wg W tlatected during preservice inspection or early in the plant life during subsequent inspwon and that crack growth is negligible over the plant life. All RCP flywheels at North Anna have been examined several times during the first ten years of operation and no cracks have been detected. Therefore, the consequences of not detecting a crack in a flywheel after 10 years of operation are considered to be negligible.

In previous reports to the NRC upon removal of the flow straighteners in 1982, it was determined that there was no impact on the external piping supports with the removal of the flow splitter plates as wall as no impact on pressure and thermal hydraulic effects.

With removal of the flow straighteners, only a portion of the stub ends extending approximately 1 1/2 inches from the reactor coolant pipe inside diameter wall remained.

Ultrasonic examinations of these flow straighteners stub ends for Unit 1 were performed during the next four refueling outages and demonstrated that base line defects had not increased. Therefore, it is considered highly unlikely that a piece of the stub end could become loose, a) The elimination of the inspection requirements for the flow straighteners and the reduction of the inspection requirements for the reactor coolant pump flywheels, as generically approved by the NRC anri supported by WCAP 14535A, do not increase the probability of an accident or malfunction of equipment important to safety previously evaluated in the safety analysis report.

The surveillance frequency changes for the RCP flywheels are based upon the results of Westinghouse Energy Systems Topical Report WCAP 14S35A These results have been reviewed, evaluated and accepted for referencing in license applications by the NRC in their Safety Evaluation Report attached to Letter entitled " Acceptance for Referencing of Topical Report WCAP 14535, Topical Report on Reactor Coolant Pump Flywheel Inspection Elimination" dated September 12,1996.

The revised surveillance requirements (inspection) only reduce the inspection requirements / frequency for the reactor coolant pump flywheels and eliminate the inspection requirements for the flow straighteners. There is no change in the method of plant operation or system design. The WCAP established that there is no increase in the risk of flyv; heel failure given ten years of inspections. The flow straighteners were previously removed and therefore are no longer present for Page 6 of 7

potential failure consideration. Therefore, the proposed changes do not increase the pr6bability of occurrence or the consequences of any previously analyzed accident.

b) The proposed changes for the el;mination of the inspection requirements for the flow straighteners, and for the reduction in inspection requirements for the reactor coolant pump flywheels, as generically approved by the NRC and supported by WCAP 14535A, do not create the possibility of an accident or malfunction of a different type than any evaluated previously in the safety analysis report.

The proposed surveillance requirements (inspection) only reduce the inspection requirements / frequency for the reactor coolant pump flywheels and eliminate the inspection requirements for the flow straighteners in Unit 1. There is no change in the method of plant operation or system design. Therefore, there are no new or different kinds of accident or rnalfunction from any accidents previously evaluated, c) The proposed changes for the elimination of the inspection requirements for the flow straighteners, and for the reduction in inspection requirements for the reactor coolant pump flywheels, as generically approved by the NRC and supported by WCAP 14535A, do not impact the accident analysis assumptions or the basis of any Technical Specifications.

The revised surveillance requirements (inspection) only reduce the inspection requiremonts/ frequency for the reactor coolant pump flywheels and eliminate the inspection requirements for the flow straighteners in Unit 1. As previously  ;

noted, the WCAP established no risk of flywheel failure given the initial ten years of periodic inspections. Additionally, the flow straighteners were previously removed and are no longer present for potential failure consideration. Therefore, the proposed changes in the surveillance (inspection) frequency do not result in a reduction in the margin of safety.

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