ML17304B316
| ML17304B316 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 06/28/1989 |
| From: | Conway W ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| To: | Martin J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| 102-01317-WFC-T, 102-1317-WFC-T, NUDOCS 8907130287 | |
| Download: ML17304B316 (7) | |
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REGULATORY INFORMATION DISTRIBUTION;SYSTEM (RIDS) )'
I ACCESSION NBR:8907130287,'OC.
DATE,: 89/06/28 NOTARIZED': YES
'OCKET g FACIL:STN-'50-529'alo'erde Nu'c'lear Station, Unit 2, Arizona Publi 05000529 AUTH.NAME AUTHOR 'AFFILIATION CONWAY,W.F.
Arizona'Public,Service Co.,(formerly Arizona. Nuclear Power RECIP NAME..'"'ECIPIENT A/FILIATION~>
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MARTIN,J.B.
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Region 5, Ofc, of.'the Director
SUBJECT:
Certifies that. steam bypass control sys fully functional.
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TITLE: Startup Report/Refueling Report (per TecE Specs NOTES:
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Arizona Public Service Company P.O. BOX 53999
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PHOENIX. ARIZONA85072-3999
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102-01317-WFC/TOS~'une 28, 1989 WILLIAMF. CONWAY EXEC UTIVE' I0 E PR ES I0 EN 7 NUCLEAR Hr. John B. Hartin, Regional Administrator Region V
U. S. Nuclear Regulatory Commission 1450 Haria Lane, Suite 210 Walnut Creek, CA 94596-5368 lz C~
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Reference:
Letter from W. F.
- Conway, APS, to J.
B. Hartin, NRC, dated June 23, 1989
Dear Sir:
Subject:
Palo Verde Nuclear Generating Station (PVNGS)
Unit 2 Restart File:
89-056'-026 On June 23, 1989 I sent you a letter certifying that Unit 2 was ready for restart with the exception of Steam Bypass Control Valve 1008.
Additionally, I stated that Unit 2 would not start up until the valve was functional.
Subsequent to my letter it was discovered that that valve's internals were not in the configuration required by the design.
Specifically, three wave springs were found in the valve rather than the one required by the design.
A formal investigation was initiated in accordance with PVNGS administrative controls.
The results of this investigation and corrective action, to date, are described in the attachment to this letter.
Steam Bypass Control Valve 1008 has been restored to its design configuration and tested satisfactorily.
This letter and attachment, certifying that the Steam Bypass Control System is fully functional, combined with the referenced letter completes the commitments made prior to restart of Unit 2.
Very truly yours, W.
Conw Executive i e President-Nuclear WFC/TDS/kj Attachment cc:
R.
P.
A. E.
S. A.
T. L.
H. J.
T. J.
A. C.
3907130287 PDR ADOCK P
Zimmerman Chaffee Richards Chan Davis Polich Gehr 890628 05000529 PDC
STATE OF ARIZONA
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COUNTY OF MARICOPA I, William F.
Conway, represent that I am Executive Vice President
- Nuclear, that the foregoing document has been signed by me on behalf of Arizona Public Service Company with full authority to do so, that I have read such document and know its contents, and that to the best of my knowledge and belief, the statements made therein are true.
William F.
Conw y Sworn to before me this
<P$
day of
- awe, 1989.
Notary Public Hy Commission Expires:
Hr. John B. Hartin Page 1
102-01317-WFC/TDS June 28, 1989 Attachment Back round On June 22,
- 1989, an initial inspection of Steam Bypass Control System (SBCS) valve 1008 internals was completed.
This inspection revealed damage to the piston ring and valve plug.
The piston ring was steam cut.
The valve plug showed evidence of higher than normal contact forces with the piston ring.
These combined impairments explained why the valve would not operate as designed.
The damage to the piston ring and plug allowed excessive steam leakage past the piston ring.
Excessive leakage past the piston ring can cause bonnet pressure to remain high when the valve is called upon to open.
The high contact forces between the piston ring and.plug resulted in increased frictional forces.
The resulting forces (high bonnet pressure and increased frictional force) can exceed the capability of the pneumatic actuator; thereby preventing the valve from opening.
More detailed investigation was required to determine the cause of the piston ring and plug deterioration.
On June 23, 1989 the assembly of SBCS valve 1008 (with internals of a new design) was allowed to progress since the new modification utilizes a modified piston ring and plug assembly and increases the capacity of the pilot valve which will enhance valve operation.
Final testing was scheduled for the following day, Saturday, June 24, 1989.
Concurrently, detailed inspections of the removed valve internals were being conducted by the system engineer and an engineer from the valve vendor, Control Components, Inc. (CCI).
The two engineers were utilizing the technical manual for the valve, CCI proprietary drawings and CCI Field Service Instructions to compare the detailed as-found conditions to the current design 'requirements for the valve in an effort to determine what caused the piston ring steam cutting and increased frictional forces.
During this inspection additional information regarding the failure of SBCS valve 1008 was discovered.
Specifically, three "wave springs" were found in the valve when only one "wave spring" was specified to be installed in accordance with current design.
The additional two wave springs resulted in the piston ring being tightly constrained when the valve bonnet hold down stud hex nuts were torqued.
This prevented the piston ring from "floating" as designed during thermal transient and other dynamic conditions.
The resulting contact between the piston ring and plug led to the damage noted on these components.
The final result being excessive steam leakage to the bonnet region and high frictional forces between the piston ring and plug.
Discussion The discovery of the two additional wave springs resulted in APS initiating a formal investigation in accordance with PVNGS administrative control procedures for incident investigations.
As part of the incident investigation, a review of the work documents which installed the wave spring modification in Unit 2 was conducted.
The results of that review are summarized below.
During April of 1988, seven (7) of the eight (8)
SBCS valves were modified to add a wave spring underneath the piston seal ring.
The remaining valve
Hr. John B. Hartin Page 2
102-01317-WFC/TDS June 28, 1989 (CV-1007) had this modification installed under a Startup Non-Conformance Report (NCR) in July of 1985.
The wave spring was designed to be installed under the piston ring to maintain contact between the top surface of the piston ring and the disk stack spacer.
The continuous contact at this interface would minimize the introduction of foreign material into the piston ring slot.
Foreign material could lead to misalignment of the piston ring with subsequent leakage past the piston ring into the valve bonnet.
As explained before, excessive leakage past the piston ring into the valve bonnet can prevent proper operation of the valve.
The modification to the SBCS valves was installed sequentially as follows:
Valve CV-1007 1st CV-1003 2nd CV-1001 3rd CV-1004 4tI1 CV-1005 5tI1 CV-1008 6tI1 CV-1002 7tI1 CV-1006 Date Wave Spring Was Installed
- July, 1985 April 08, 1988 April ll, 1988 April 12, 1988 April 12, 1988 April,15, 1988 April 20, 1988 April 21, 1988 Implementing Document NCR-SJ-5907 WO ¹00286252 WO ¹00286241 WO ¹00286253 WO ¹00286254 WO ¹00286256 WO ¹00286251 MO ¹00286255 A review of the Request for Stores (ROS), related to the above work orders, showed that seven (7) wave springs were initially issued to work on the seven (7) valves in question (ROS ¹212960).
Reassembly of the SBCS valve internals proceeded in the sequence shown above using the seven wave springs until CV-1002 reassembly began.
At this time, it was noted that all seven wave springs had been used.
Two additional ROS's
(¹211350 and ¹211349) were then issued to acquire the two (2) wave springs necessary for reassembly of CV-1002 and CV-1006.
- Thus, a total of nine (9) wave springs had been issued for work on the seven (7) valves which were being modified in April of 1988.
Based on the logic presented below, it is concluded that one (1) wave spring was installed in six (6) valves, and three (3) wave springs were installed in CV-1008.
To ensure that the installation of three (3) wave springs in CV-1008 was in fact an isolated incident, the following logic was employed to ensure that all seven SBCS valves, which were modified during the April 1988 time-frame, are configured as designed:
1.
Valve CV-1008 accounted for three (3) of the initial seven (7) wave springs issued.
2.
The remaining four (4) wave springs from the initial seven (7) are installed in CV-1001, CV-1003, CV-1004, and CV-1005.
Based on disassembly and inspection of CV-1001,
- 1003, and 1004, which confirmed that each va1ve contained only one wave spring, it is concluded that CV-1005 has only one wave spring.
3.
Valves CV-1002 and CV-1006 accounted for the additional two (2) wave springs issued.
Mr. John B. Martin Page 3
102-01317-MFC/TDS
'une 28, 1989 Following disassembly and inspection of CV-1001,
- 1003, and
- 1004, these valves were reassembled with a modified piston ring and plug assembly as previously discussed.
During the disassembly and inspection of these valves, stackup dimensions were taken and close examination performed with no abnormalities noted.
To ensure there was no replication of this event to the Unit 1 or Unit 3
- valves, the internals of all eight Unit 3 SBCS valves and 3 of the Unit 1
SBCS valves were inspected by the system engineer and the Lead Balance of Plant Engineer.
No abnormalities were discovered.
Of the remaining five valves in Unit 1, the wave spring modification was never implemented on four of the valves and the fifth valve currently has the modified internals installed.
Prior to return to service of Unit 1 and Unit 3 all SBCS valves in those units will have the modified piston and plug assembly installed.'lthough the Atmospheric Dump Valves (ADVs) are similar to the SBCS valve in design, their internals have been modified by the installation of a new plug
- design, a two piece piston ring, and a modified disk stack.
There is not, nor has there ever been a modification to the ADVs which installed a wave spring under the piston ring.
Currently, all eight Unit 2 SBCS valves have been tested and are considered completely functional and reliable.
Four of the valves contain the modified piston ring and plug assembly, and four of the valves contain the wave spring modification described on page 2 of this attachment.
The four valves without the improved internals will be modified as soon as parts become available and plant conditions permit following Unit 2 restart.
The complete detailed investigation to determine why the three wave springs were installed in CV-1008 is in progress with an expected completion date of July 21, 1989.
This is not considered a restart issue since all Steam Bypass Control valves are functional.
~Sammar Based on a review of the work orders which implemented the wave spring modification, the inspections conducted on the four Unit 2 SBCS valves and the applicable Unit 1 and Unit 3 SBCS valves, and satisfactory operation of all the Unit 2 SBCS valves, APS believes no additional jnspections of the Unit 2 SBCS valves are necessary and the SBCS is fully functional.
- Also, an inservice surveillance program is in place to periodically (every 2 weeks) check the functionality of the SBCS valves.
Additionally, SBCS functionability will be demonstrated during ADV testing as the ADV steam flow will be balanced by a SBCS valve during the monthly ADV stroke testing.
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