ML20080G428

Rev 1 to Interim Deficiency Rept DER 83-49 Re Impeller Blades & Diffuser Bolts Broken/Loose in Reactor Coolant Pumps.Initially Reported on 830715.Final Rept Will Be Submitted by 840615.Results of C-E Review Encl

ML20080G428
Person / Time
Site:	Palo Verde
Issue date:	01/27/1984
From:	Van Brunt E ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	Bishop T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
References
ANPP-28733-BSK, DER-83-49, NUDOCS 8402130386
Download: ML20080G428 (7)

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' Arizona Public Service Company

" P.O. Box 21666 . PHOENIX, ARIZONA 8SOM January 27, 1984 ANPP-28733-BSK/KCP

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r 1 A U.'S.' Nuclear Regulatory Commission Region V f Creekside Oaks Office Park

.c 1450 Maria Lane - Suite 210

1. - Walnut Creek, CA'94596-5368 L

. Attention: Mr. T. W. Bishop, Director Division of Resident

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Keactor Projects and Engineering Programs

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'Su *,e c t : InterimRepord, Revision 1-DER 83-49 A 50/55(e) Potentielly Reportable Deficiency Relating to Br an Impeller Blades and Diffuser Bolts Broken / Loose In

".. actor Coolant Pumps

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84.-019-026; D.4.33.2 7

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Referdnce: A) Telephone Conversation between P. Narbut and R. Tucker

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on July 15, 1983 .

b _- B) Telephone Conversation between T. Young and R. Tucker on July 18, 1983 6 >C) ANPP-27593,' dated August 19, 1983 (Interim Report)

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D) ARPP-28734, dated January 27, 1984 (DER 63-30 Interim. Report, Revision'l)

'[ ' E) ANPP-28313, dated, November 29, 1983 (Time Extension)

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Dear' Sir:

7 The NRC was notified"of two potentially reportable deficiencies in References (A) and,(B). Intetim. Reports were submitted in References (C) and (D), and a Time Extension requested in Reference (E). At that' time,

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t j J' - .it was estinated that"a Final Report would be submitted by January 27, j 1984.>

y;y ;j Due't'o the duplication of information and reporting involved, DER 83-50 is being combined with and transierred to DER 83-49, in accordance with h .the revised Interite Report attached and as discussed with Mr. Paul Narbut It is expected that this information will be finalized 9 O.;< by of your June 15, office.1984, at which time a complete report will be submitted.

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Very truly .ours 4

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8402130386 840127 ._E. E. Van Brunt, Jr. ,

PDR ADOCK 05000528 APS Vice President, Nuclear U PDR -. ANPP Project Director 3

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Attachment:

CE Doc. No. CEN-271(V)-P

. Proprietary Copy #1

'cc: See Page TwoL )7 ec

Mr. T. W. Bishop DER 83-49 Page Two C E Doc. No. CEN-271(V)-P Proprietary Copies cc: Richard DeYoung, Director #2 Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission Washington, D. C. 20555 T. G. Woods, Jr.- #3 G. C. Andognini

• J. A. Roedel *

.D. B. Fasnacht A. C. Rogers

• B. S. Kaplan

• W. E. Ide

• J. Vorees J. R. Bynum

• D. D. Green P. P. Klute

• A. C. Gehr #4 W. J. Stubblefield #5 W. G. Bingham. #6 R. L. Patterson # 7-R. W. Welcher' #8 R. M. Grant #9 D. R. Eawkinson #10 L. E. Vorderbrueggen #11 G. A. Fiorelli #12 S. R. Frost

• J. Self D. Canady

• Records Center Institute of Nuclear Power Operations

• 1100 circle 75 Parkway, Suite 1500 Atlanta, GA 30339 Mr'..E. Licitra, Project Mang er- #13 through #37 U.S. Nuclaar Regulatory Commission and 2 non proprietary Phf.llips Building copies

. 7920 Norfolk' Avenue Bethesda, Maryland 20814 File: DER 83-49 #38

• Non proprietary copy attached.

INTERIM REPORT - REVISION 1 - DER 83-49 POTENTIAL REPORTABLE DEFICIENCY ARIZONA PUBLIC SERVICE, COMPANY (APS)

PVNGS UNIT 11' I. Potential Problem After precore hot functional testing, the PVNGS Unit 1 Reactor Coolant Pump (RCP) 1A was disassembled to excavate a linear indication in the pump casing circumferential weld. An inspection of the pump internal assemblies revealed four (4) broken and two (2) loose diffuser to casing retaining cap screws. Additionally, ten (10) of the diffuser to suction pipe cap screws were found to be loose. There was also slight cavitation damage observed on the leading edge of seven (7) diffuser vanes.

As a result of this inspection, the other three (3) Unit 1 RCP's were subsequently disassembled and inspected. In addition to discovering loose and/or broken diffuser and suction pipe cap screws, the following discrepancies were found:

1. The pump casings had sustained fretting or peening damage.

2. The leading edges, of one impeller vane on RCP IB and two (2) vanes on RCP 2A 3 were missing segments. Impeller and diffuser degradation was observed.

3. There were broken and/or loose impeller key retaining screws, shaft pre *.ection sleeve key retaining rings, and carbon journal bearing key retaining screws.

4. The shaf t seals showed wear on the stationary seal ring holders, and heavy deposits of 0-ring lubricant throughout the seal assemblies.

It was also reported that bolts in the seal cartridges were loose.

5. ' Leakage was observed between the carbon bearing sleeve and the seal housing indicating seal ring failure.

6. Surface indications such as scratches, burrs, wear marks, and ARC strikes were also obseried.

The PVNGS Reactor Coolant Pumps are supplied by Combustion Engineering (C-E) and are designed by KSB of West Germany.

II. Approach to and Status of Proposed Resolution C-E has reviewed the potential failure mechanisms and their ,

consequences. These include a locked rotor, degraded pump coast down and core flow blockage. The results of the investigation are as follows:

5867A/1510A

T. W. Bishop Interim Report, Revision 1 - DER 83-49 Page Three .

II. Approach to and Status of Proposed Resolution (cont'd)

4) The function of the key retaining screws is to hold the keys in place during assembly operations. Once the impeller and carbon journal bearing is assembled, tha keys and retaining screws are captured within the assemblies. Failure or loosening of the key retaining screws will not affect pump operability or result in discharde of parts in the RCS. The loose bolts in the seal cartridges are attributed to the high vibration levela experienced because of the impeller and diffuser deficiencies previously reported. Since the seal cartridges are above the water lubricated bearing, any bolts or seal parts could not pass through the close clearance bearing into the RCS.

5) The purpose of the seal ring between the bearing sleeve and the seal housing is to prevent the exchange of water between the pump casing / impeller discharge area and the cooler water lubricated carbon bearing area. Leakage past the seal ring could upset water circulation within the bearing, however, the bearing would continue to function and would not affect pump coast down capabilities.

.6) The total assessment of the effect of the aforementioned deficiencies shows that the Reactor Coolant Pumps will maintain sufficient flow to satisfy the criteria set forth in the safety analysis.

An intensive program was initiated by C-E, C-E KSB, and KSB (West Germany) to determine the causes of these deficiencies, and the modifications necessary to correct the problems. Additionally, a progrse to verify the modifications by model and prototype testing has been established. The programs completed or presently underway are as follows:

1) Model tests with increased impeller / diffuser gaps to evaluate the reduction in pressure loadings on the diffuscr/ casing and diffuser / suction pipe joints. The model tests are necessary to determine the effectiveness of increased gaps to eliminate the diffuser vane leading edge cavitation.

Model tests also verify known impeller stresses, and look for additional loadings which may result from higher than anticipated rgr.out flows.

2) A complete evaluation of the diffuser and suction pipe cap screw stresses considering imposed loads, bolt preload, dimensional tolerances and stack up and assembly techniques.

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T. W. Bishop Interim Report, Revision 1 - DER 83-49 Page Four . ,

II. Approach to and Status of Proposed Resolution (cont'd)

3) 'A metallurgical investigation of the adequacy of the cap screw and impeller materials. Preliminary results show that both the cap screws and impellers are in compliance with the required material specifications.

4) Protctype testing in the CE-KSB test loop to collect base line data on the hydraulic components as originally designed and as modified.

.This testing also includes verification of the adequacy of diffuser

-retention modifications.

5) . Examination of the broken impeller key retaining screws indicated that the sockets in the heads were formed too deep. This resulted 1pinsufficientwallthicknessintheheadtoshankarea. The replacement screws have been redesigned with a large head to a!ccommodate the socket. Tighter manufacturing control has been employed to insure that the sockets'are not broached too deep.

These screws will also be installed with retaining sleeves and staked in place.

.The shaft protection sleeve and carbon journal bearing key retaining screws are smaller screws .and their looseness is attributed to high pump vibration. The method of torquing these screws and the possibility of. staking them is being investigated.

6) The bearing sleeve to seal housing seal ring will be replaced with a flexitallic type gasket. The size of the bolts in the joint has been increased to insure that the ' gasket is properly seated.

7) The solution to the shaft seal, deficiencies are not as critical and the investigations are more'long' term. Excessive "O" ring lubrication can lead to reduced' seal life'and instructions will be issued on the proper use of the lubrication. Precautions will also be taken to insure that the seal cartridge bolts'are properly torqued;

8) 'A special test program -for Unit 1, to demonstrate the adequacy of the modifications to the. Reactor. Coolant Pumps, will take place prior to fuel load. An operating sequence has been developed to test the modified components, under conditions similar to those during which the damage occurred, This program is scheduled for April 1984. .

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T. W. Bishop Interim Report, Revision 1 - DER 83-49 Page Two ,

II. Approach to and Status of Proposed Resolution _ (cont'd)

1) The discovery of loose and/or broken diffuser bolting could cause diffuser movement and subsequent impeller binding. However, during full power operation hydraulic forces alone can maintain the diffuser in place. Only during start-up or coast down is there any potential for axial movement of the diffuser. The design is such that the diffuser-suction pipe assembly is captured radially throughout any axial movement. The diffuser cannot rotate because it is restrained by two (2) keys which engage the mating pump casing

-ledge. With these design features, the potential for impeller binding is remote during start-up and coast down.

2) Loose diffuser to suction pipe cap screws resulted in some movement of the diffuser / suction pipe assemblies as evidenced by wear on the suction pipe seating surface and the diffuser ledge in the pump casing. However, there was no evidence of impeller binding. The keys in the diffuser to casing joint prevented radial movement of the diffuser halves. The RCP's with the broken impeller vanes did show some minor scratching on the impeller wear surfaces, but not of sufficient magnitude to affect pump coast down.

3) The potential for core flow blockage has been examined, and it has been concluded that the observed deficiencies would not lead to flow blockage.

The radial gap between the impeller and diffuser is small enough to prevent the escape of particles that are large enough to cause local flow blockage. This conclusion was verified in RCP 1A, in that the three (3) broken diffuser cap screw heads which came free f rom their locking sleeves did not pass through the impeller / diffuser gap.

The broken impeller vane segments were found in the flow skirt of the reactor vessel because they were too large to pass through the j flow skirt. The long cracks found in the damaged impellers indicate !

that any additional segments would be too large to pass through the

• flow skirt. t i

-Any particles generated from the diffuser vane leading edge cavitation would be microscopic in size, and would not lead to core flow blockage. The diffuser vane cavitation observed was minor and no material was found in the Reactor Coolant System (RCS) which could be identified as diffuser material. .

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T. W. Bishop Interim Report, Revision 1 - DER 83-49 Page Five - .. ,

I II. Approach to and Status of Proposed Resolution (cont'd) 2

9) .Bechtel will implement the required corrective action prior.to the above mentioned demonstration test via the following Design Change Packages (DCP's).

ISM-RC-107 ISM-RC-109 ISM-RC-113 Additionally, these changes will be implemented in Units 2 and 3 prior to fuel load via DCP's.

2SM-RC-107 3CH-RC-107 2SM-RC-109 3CM-RC-109 2SM-RC-ll3 3CM-RC-113 These DCP's'will provide the corrective action disposition of NCR's SM-2657, -2658, -2659, and -2660.

Additional information is provided in the attached C-E Interim Report,

. "Palo Verde Nuclear Generating Station Unit #1 Reactor Coolant Pumps (Proprietary)."

III. Projected Completion of Corrective Action and Submittal of the Final /

Report

-Evaluation of this condition and submittal of the Final Report is forecast to be completed by June 15, 1984.

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