ML20059M812
| ML20059M812 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 08/17/1993 |
| From: | Rueger G PACIFIC GAS & ELECTRIC CO. |
| To: | |
| References | |
| OLA-2-I-MFP-022, OLA-2-I-MFP-22, NUDOCS 9311190348 | |
| Download: ML20059M812 (10) | |
Text
_ _ _ _ _ _ _ _ _ _ - _ _ - _ _ - _ _ _ - _ _ _ _ _ _ _ _ _ _ - _ - _ _ _
eYhiboT 2 L 1l 60
- 2. '75 324 -Ol ft ~~2-
~N$ acific Gas and Electric Company 77 Beale Street. Room 1451 Gregory M. Rueger PO Box 770000
.Senjor Vice President and San Francisco.CA 94177
., 'Ge$ral Manager
,Halear Power Generation -
415/973-4684 Far 415S73-2313
'93 0"~ 28 P6 :16 July 28, 1993 PG&E Letter No. DCL-93-191
,y U.S. Nuclear Regulatory Commission ATTN: Document Control Desk i
Washington, D.C.
20555 Re:
Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Units 1 and 2 Licensee Event Report 2-93-006-00 Anchor-Darling Check Valve Bonnet Dowel Pins Not in Compliance with Design Requirements Due to Manufacturing Error Gentlemen:
9 Pursuant to Item 19 of Supplement I to NUREG-1022, PG&E is submitting the enclosed voluntary Licensee Event Report 2-93-006-00 regarding the discovery of dowel pins of insufficient length in Anchor-Darling check-valves. These events did not affect the health and safety of the public.
Sincerely, t
}
4 Gregory M. Rueger cc:
Bobby H. Faulkenberry Ann"P. Hodgdon u
Mary H. Miller Sheri R. Peterson CPUC Diablo Distribution INP0 DCO-93-MM-N016 Enclosure NUCLEAR REGULATORY CoMMrtst0N 1142S/85K/KAB/2246 777p/L J2A o,w,,g ;79.C L+
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LICENSEE EVENT REPORT (LER)
PAof m DIABLO CANYON UNIT 2 Ol5l0lOl0l3l2l3 1l 'l 9 '
ANCHOR-DARLING CHECK VALVE BONNET DOWEL PINS NOT IN COMPLIANCE WITH DESIGN REQUIREMENTS mts i i DUE TO MANUFACTURING ERROR EVENT DATI(El LIM NUMSER ten REPORT DATE (76 OTHER F ACIUTIES tNVOLVED (St MON DAY YR YR SEO NTIAL REV1 ON MON DAY YR DOCKET NUMBER ESI 5
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DIABLO CANYON UNIT 1 03 10 93 93
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OPsRArimo fees REPOR r is sumANTTED PUR&UANT TO THE REQUIREMENTS OF 10 cm. (116 MODE toi 10 CFR tavEL 01010 VOLUNTAR1 X
OTHER tion
($reCify in Abstr iCt below and in text, WRC form 366A)
UCEN5ff CONT ACT FOR 7655 Lept (12}
DAVID P. SISK, SENIOR REGULATORY COMPLIANCE ENGINEER
- at^ cat 805 545-4420 COMPLETE ONE UNE FOR EACH COMPONENT F AiLURE DESCResED IN 16es REPORT 113)
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SUPPLEMENT AL REPORT EXPECTED 1141 EXPECTED
$UBMISSION DATE W ll YES (if yes, Complete EXPECTED SUBMISSION DATE) lX l NO AuTRACT (1.i This voluntary licensee Event Report is submitted for information purposes only as described in Item 19 of Supplement I to NUREG-1022.
On March In.1993, during inspection of containment spray check valve CS-2-9002A in the Unit 2 fifth refseling outage, the bonnet done. pins indicated on tne Anchor-Darling (A/D) vendor drawing were initially thought to be missing.
-~
On March 17, 1993, in preparation for dowel pin installation,. further investigation identified that the dowel pins were not missing from CS-2-9002A as initially thought.
The dowel pins had been manufactured to an insufficient length, causing them to fall into and become flush with the bonnet surface upon opening the valve.
An evaluation of this condition determined that insufficient dowel pin length would not affect the operability of the valve.
1 On March 26, 1993, inspections of similar Unit 2 A/D check valves that perform safety-related functions identified another dowel pin of insufficient length.
All similar Unit 2 A/D check valves performing safety-related functions were returned to the correct design requirements as necessary during the fifth refueling. outage for Unit 2.
Inspections and necessary repairs of all similar Unit 1 A/D check valves that perform safety-related functions will be completed during the sixth refueling outage for Unit 1.
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Plant Conditions Unit 2 operated in various modes at various_ power levels with the conditions described below.
II.
Descriotion of Event A.
Summary:
On March 10, 1993, during inspection 'of containment spray check valve (BE)(V) CS-2-9002A, the bonnet dowel pins indicated on the Anchor-Darling (A/D) vendor drawing were initially thought to be missing.
On March 17, 1993, in preparation for dowel pin installation, further investigation ideniliieu tiint the dowel pins were not missing from CS-2-9002A as initially thought. The dowel pins had been manufactured to an insufficient length, causing them to fall -into and become flush with the bonnet surface upon opening the valve.
On March 26, 1993, inspections of the Unit 2 A/D check valves that perform safety-related functions identified another dowel pin of insufficient length in safety injection valve (BQ)(V) SI-2-8977.
B.
Background:
The A/D swing check valve is constructed with the check valve disk articulated from the swing arm hinged at hinge blocks attached to a loose fitting hinge plate (Figure 1).
The hinge plate is restrained from rotation in the valve bore by a locking pin to prevent rotation.
1 The hinge plate is restrained from vertical movement by two dowel pins l
180 apart (aligned w G. the valve inlet / outlet axis) that extend from
~
the bonnet flange to 0.020 to 0.090 inches above the hinge plate.
This design provides for the upstream dowel pin preventing the loose-fitting locking pin from moving'out of position.
Surveillance Test Procedure (STP) V-18, " Check Valve Inspection,"
partially implements the In-Service Inspection for certain check valves, including CS-1-9002A and B, CS-2-9002A and B, SI-1-8977, and SI-2-8977.
C.
Event
Description:
1 On March 10, 1993, during inspection of containment' spray check valve CS-2-9002A in the Unit 2 fifth refueling outage (2RS), the bonnet-dowel pins indicated on the A/D vendor drawing were-initially thought to.be missing.
This inspection was performed in accordance with.
STP V-18 as part of the check valve-inspection program.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION
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On March 10, 1993, in a telephone conversation with PG&E, the check valve's manufacturer, A/D, indicated that the dowel pins are required to hold the hinge ring down during a seismic event to prevent improper disk reseating and subsequent potential for reverse flow (Figure 1).
PG&E subsequently performed a component search that identified a total of 12 (six cer unit) eight-inch check valves of this design (model number 2588-5) installed in the plant.
Of this population,~ CS-2-9002A was the only one that had not been previously inspected under the check valve inspection program and STP V-18.
PG&E believed that.since previous inspections had utilized the same drawing which identified the missing dowel pins on CS-9002A, any condition of pins 'nissing from the other valves would have been detected.
Therefore, the condition found on CS-2-9002A was initially thought to be an isolated case.
On March 16, 1993, PG&E discovered that the vendor drawing was in I
conflict with the dowel pin installation instructions provided by A/D l
in the March 10, 1993, telephone conversation.
A/D had corrected the i
l drawing errors in Revision F in 1984; however, PG&E's latest drawing l
revision was Revision E.
l l
On March 17, 1993, in preparation for dowel pin installation, further investigation determined that the dowel pins had been installed by A/D on CS-2-9002A, but the dowel pins as specified on the incorrect early revision of the design drawing, Revision E, were of an insufficient length. When the valve was opened and inspected on W h 10, 1993, the dowel pins had fallen into the bonnet, flush with the bonnet surface, giving the appearance as though there were no pins or holes.
On March 18, 1993, a total of 28 (14 per unit) A/D check valves were
'"~ identified to be*fittalled at Diablo Cmiyon that utilize Gal pins e
for proper retention of the hinge ring.
This. population consists of the 12 eight-inch valves of model number 2588-5 previously identified, plus 16 four-inch valves of model number 2587-5.
Of the entire population, PG&E decided to inspect all valves that perform safety-related functions.
Subsequent inspections of the Unit 2 A/D check valves that perform safety-related functions identified another short dowel pin in safety injection valve SI-2-8977, as well as the following additional conditions of noncompliance with the design requirements (Figures 1 and 2):
i i
1.
insufficient hinge ring locking pin length.
2.
inadequate gasket crush (lack of metal-to-metal contact between the bonnet body and the bonnet cover) causing the gap between the bonnet and the hinge ring to exceed the 0.090-inch limit.
3.
90 rotation of the bonnet cover so that the upstream dowel pin and the locating pin are not vertically aligned.
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TFJT ilh Each of the above conditions contributes to the potential for the locking pin to disengage during a seismic event, allowing the hinge l
ring to rotate and preventing the disk from properly reseating.
On April 2,1993, an evaluation concluded that the Unit 1 A/D check valves c. hat perform safety-related functions and that could potentially have the above deficiencies did not pose any unreviewed safety question.
On April 5,1993, PG&E submitted a letter to Westinghouse (the supplier of the A/D check valves) informing them of the deficient conditions for consideration as a potential 10 CFR 21 reportability concern.
By April 1,1993, inspections and required corrections of the Unit 2 valves providing safety-related functions were complete, assuring the adequacy of the installation.
l A review of the applicable maintenance history concluded that no maintenance had been performed by PG&E on any of the subject valves that could have altered the configuration of the dowel pins.
D.
Inoperable Structures, Components, or Systems that Contributed to the Event:
None.
E.
Dates and Approximate Times for Major Occurrences:
1.
March 10, 1993:
Event / discovery date.-,Jhe bonnet dowel pint indicated on the vendor drawing appeared to be missing from containment spray valve CS-2-9002A.
2.
March 16, 1993:
PG&E discovered that the vendor drawing was an old revision that contained errors.
3.
March 17, 1993:
PG&E discovered that the bonnet dowel pins were not missing from CS-2-9002A, but had been manufactured to the incorrect length, and were flush with the bonnet.
4.
March 26, 1993:
Inspections of safety-related Unit 2 A/D check valves identified another short dowel pin on SI-2-8977.
5.
April 5, 1993:
PG&E submitted a letter to Westinghouse, informing them of the deficient conditions.
l
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION
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April 13, 1993:
Inspections and required corrections of the i
Unit 2 valves providing safety-related functions were complete, assuring the adequacy of the installation.
F.
Other Systems or Secondary Functions Affected:
None.
G.
Method of Discovery:
As part of routine inspections and related evaluations of safety-i related check valves during 2R5, PG&E personnel identified the discrepant conditions.
l H.
Operator Actions:
None.
I.
Safety System Responses:
None.
l III.
Cause of the Event l
l A.
Immediate Cause:
CS-2-9002A and 51-2-8977 contained dowel pins of insufficient length.
B.
Rooj,Cause:
The root cause of these events was manufacturing error, in that the l
manufacturer supplied PG&E with equipment and drawings that did not comply with the original design requirements.
IV.
Analysis of the Event If the dowel pins were not installed or were capable of movement into the bonnet, the hinge plate could move upwards and out of position during a seismic event with vertical accelerations of 1.0g or greater at the valve location.
After the seismic. event, the hinge plate may not return to its original position.
This disk-to-seat misalignment would allow the valve to leak through in the reverse flow direction. The operability of the valve in the forward flow direction would not be affected due to restraint afforded by the valve bonnet, i
4
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION i
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,w on Reverse flow leakage poses a potential issue with respect to the ability of the valve and associated system to perform their design function. Out of the total population of 28 valves of models 2587-5 and 2588-5,16 (eight per unit) perform safety-related functions and were determined to pose a potential safety concern.
The eight valves of concern were CS-9002A and B, CS-90llA and B, SI-8924, SI-8977, CVCS-8440 (CB)(V), and RCS-8028 (AB)(V).
The design of the A/D check valve iMernals is such that during all conditions of normal operation (opudng and closing), the valve disk is i
driven to be self-centering toward the valve seat, as confirmed by the vendor.
However, the vendor has also confirmed that a seismic event of sufficient strength could cause the hinge r'ng to move upward and the locating pin to disengage, resulting in disk misalignment.
A component which has been discovered to lack full seismic qualification may be determined to be operable if all of the following conditions are met:
1.
Following a seismic event, the component will function satisfactorily or failure will not prevent safe shutdown of the unit (a coincident loss-of-coolant accident (LOCA) is not considered a design basis event for operability evaluations).
2.
The component will function properly (or will not prevent the proper safety-related function of other components) for all required accident conditions (LOCA, high energy line break, abnormal operating condition, etc.), except following the postulated seismic event.
3.
The component will be repaired or replaced at the next unit outage of sufficient duratio:..
The described condition is acceptable based upon the following:
1.
Diablo Canyon Emergency Procedure (EP) M-4, " Earthquake," requires that the Unit be brought to Mode 5 (Cold Shutdown) in an orderly manner for evaluation of all potentiaily affected plant equipment for a seismic event with a base mat (ground) acceleration equal to or greater than 0.29 All suspect valves are located in lines such that i
less than 1.0g vertical acceleration would be seen at the valves for a containment base seismic event of 0.2g or less.
An upward seismic force greater than 1.0g is required to affect any significant hinge ring movement.
[
i 2.
Diablo Canyon Reactor Protection System, functional Unit 23 " Seismic Trip," is initiated to promptly trip the reactor (AB)(RCT) in the event of a seismic event greater than 0.35.
9 3.
The probability of a concurrent (or closely coupled) seismic and LOCA event is sufficiently lc.. that the margin of safety relied upon in the FSAR Update is not significantly altered.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION e
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Based on the above discussion, the condition described ir, this LER does i
not affect the health and safety of the public.
V.
Corrective Actions A.
Immediate Corrective Actions:
1.
All Unit 2 A/D valves of model numbers 2587-5 and 2588-5 which j
perform safety-related functions were returned to the correct i
design requirements as necessary during 2RS.
2.
All Unit 1 A/D valves of model numbers 2587-5 and 2588-5 which perform safety-related functions will be inspected and repaired as necessary during the Unit I sixth refueling outage.
3.
PG&E is revising the affected design drawing to document the dimensional requirements and fabrication details that were obtained from A/D for the inspection and maintenance of the four and eight-inch A/D check valves.
B.
Corrective Actions to Prevent Recurrence:
The A/D check valves of model numbers 2588-5 and 2587-5 were not manufactured to the correct design requirements. Therefore no corrective action to prevent recurrence is required by PG&E.
VI.
A:iditioiial Information A.
Failed Components:
None.
m.
n B.
Previous Similar LERs LER 2-88-014-00, " Anchor-Darling Check Valve Retaining Block Stud Breakage Due to Intergranular Stress Corrosion Cracking" This previous LER reported PG&E's discovery of retaining block stud breakage in A/D check valves due to intergranular stress corrosion cracking (as was later reported in NRC Information Notice 88-85).
The root cause of this previous event was incorrect heat treatment of the studs by the manufacturer, and the corrective actions to prevent recurrence were to replace the studs with those made of properly heat treated material.
This corrective action could not have prevented the use of the short dowel pins.
I
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l Figure 2 Parts List l
1.
Bonnet body
- 11. Gasket l
2.
Bonnet cap
- 12. Seat ring j
3.
Disc
- 13. Washer i
4.
Hinge
- 14. Set screw l
S.
Hinge ring
6.
Nut
- 16. Locking pin 7.
Hinge pin
- 17. Name plate 8.
Wire
- 18. Welding rod 9.
Stud
- 19. Bushing
- 10. Nut i
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