ML20059M817
| ML20059M817 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 08/17/1993 |
| From: | AFFILIATION NOT ASSIGNED |
| To: | |
| References | |
| OLA-2-I-MFP-023, OLA-2-I-MFP-23, NUDOCS 9311190353 | |
| Download: ML20059M817 (19) | |
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NCR: DC493.MENQ16 DRAFT: egg,,@3 NCR DCO-93-MM-N016
'93 OC' 28 P6 :16 ANCHOR DARLING CHECK VALVE COVER DOWELS DRAFT: JUNE 02, 1993 h,ii:
? 4 3 MANAGEMENT
SUMMARY
On March 10, 1993, during inspection of containment spray check valve CS-2-9002A, it appeared as though the bonnet dowel pins indicated on the vendor drawina were missing.
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.
On March 17, 1993,'further investigation revealed that the dowel pins had been installed on CS-2-9002A, but had been manufactured to the incorrect length as specified en Revision E.to the associated design drawing.
A total of 28 (14 per unit) A/D check valves'are installed at DCPP that utilize dowel pins for proper retention of the' hinge ring.
Of this population, PG&E decided to inspect all. valves that perform a safety related function.
Subsequent inspections of the Unit 2 A/D check valves that perform a safety related function revealed another short dowel ein in safety injection valve SI-2-8977.
An Operability Evaluation (OE) was generated to address the-potential for similar conditions to. exist on Unit 1.
OE 93-04 concluded that the Unit 1 A/D check valves of concern did not i
pgse an unreviewed safety question.
These valves will ba i
~
n.opected during 1R6.
l During the remaining Unit 2 inspections, PG&E' discovered additional conditions of non-compliance with the design requirements.
All problems were noted and' corrected.
The root cause of this event is that the vendor of the' valves supplied PG&E with equipment that did not comply with the design-requirements.
I This event will be reported to the NRC via voluntary !.ER 1 004-00.
l The closure date for this NCR is' June 15, 1994.
1 93NCRWM93MMN016 KAB Page 1
of 19 9311190353 930817 PDR ADOCK 05000275
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l NCR: DCtM3-MM N016 DRAFT: JUNE 02,1993 NCR DCO-93-MM-N016 ANCHOR DARLING CHECK VALVE COVER DOWELS l
I.
Plant Conditions Unit 1 was in Mode 1 (Power Operation) at 100% power and Unit 2 was in Mode 6 (Refueling) at 0%_ power.
II.
Descriotion of Event A.
Summary:
On March 10, 1993, during inspection of containment spray check valve CS-2-9002A, it appeared as though the bonnet dowel pins indicated on the vendor drawing were missing (ref. 1 and 2).
On March 17, 1993, in preparation for dowel pin installment, further investigation revealed that the dowel pins had been installed on CS-2-9002A, but had been manufactured to the incorrect length as specified on Revision E to the associated design drawing.
On March 26, 1993, inspections of the Unit 2 A/D check valves that perform safety related functions revealed another short dowel pin in safety injection valve SI 8977, as well as other conditions of non-compliance with the design.
B.
Background:
The A/D swing check valve is constructed wijp the check valve disk articulated from the soing arm hinged at hinge blocks attached to a loose fitting hinge plate.
The hinge plate is restrained from lateral movement by the hinge plate outside diameter to valve body bore (approximately a.010" to.070" clearance)..The hinge plate is restrained from rotation in the valve bore by a locking pin to prevent rotation.
The hinge ~ plate is restrained from vertical movement by capture between the valve body bore landing from below and the valve bonnet (hold down) dowels.. Hinge plate restraint _is accomplished by two dowels 180 apart (aligned with the valve inlet / outlet axis) that extend from the bonnet flange to 0.020" to 0.090" above the hinge plate.
This design provides for the upstream hold down dowel to prevent the loose fit locating pin from moving out of position.
93NCRWP;93MMN016 KAB Page 2
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I NCRs DCG93-MM-N016 DRAFT: JUtst.u2.1993 If the hold'down dowels were not, installed (or were-i capable of movement into the bonnet),'during a. seismic l
event resulting in vertical accelerations of 1.0 g'or greater at the valve the hinge-plate could: move-upwards, out'of' position,.untilorestrained by-the valve bonnet.
After the~ seismic event-the. hinge plate may.
7 not return to its original position. This ' movement:
would raise the check valve disk approximately the same amount as the movement. or approximately 3/8".
.This disk toLseat misalignment would allow.the valve to-leak through in the reverse flow direction. :The operability' of the valve in the forward. flow would not=be affected due.to restraint' afforded by the valve, bonnet.
C.
Event
Description:
On March 10, 1993, during inspection of containment.
spray check valve CS-2-9002A, fit appeared as;though<the-l bonnet dowel pins ^ indicated on the' vendor drawing were missing (Ref. 1 and 2).
This inspection was performed in accordance with Maintenance Procedure (MP) M-51.14.
In a telephone conversation with PG&Ej the. valve's..
manufacturer, Anchor-Darling (A/D),-indicated'that the dowel pins are required to hold the hinge ring (Ref.12)-
~
down during a seismic event, to prevent improper-disk-y i
reseating and subsequent potential for3 reverse flow
- j fRef. 1).
PG&E subsequently performed a. component historyfsearch-l which identified a total of 12 eight-inchscheck valves 1
l of-this design installed in.the plant..
Ofl thia:
population, CS-2-9002A was the only one'that had never been inspected under theLCheck Valve Program and STP.V-15 (Ref. 1).
_PG&E believed that. since previous inspqctions had utilized the same drawingtwhich identified the missing ~ dowel-pins on.CS-9002A, any.
condition of pins missing from the other valves would have been detected.
Therefore,-the condition found on 4
CS-2-9002A was thought to;be_an; isolated' case.
On March 16, 1993, PG&E discovered!that1the. vendor drawing was in conflict with'the dowel pin installation instructions provided'by A/D.in the; March ~10 telephone conversation.
A/D had' corrected the" drawing 'errorsfin 4
Revision F in 1984; however,-PG&E was in possession of Revision E.
93NCRWP93MMN016 KAB
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NCR: DC093-MM-N016 DRAFT; JUNE 02,1993 i
On March 17, 1993, in preparation for dowel pin j
installment, further investigation revealed that the dowel pins had been installed on CS-2-9002A, but had been manufactured to the incorrect length as specified on Revision E to the drawing.
When the valve was opened and inspected on March 10, the dowel pins had fallen into the bonnet, fluch with the bonnet surface, giving the appearance as though there were no pins.
PG&E assumed that previous check valve inspections j
would have detected any short pins in the inspected valves, and any problem would have been corrected.
This was based on the fact that the same drawing and inspection procedure that' detected the condition in CS-2-9002A were used for previous inspections.
On March 18, 1993, a Prompt Operability Assessmer.
(POA) identified a total of 28 (14 per unit) A/D check valves installed at DCPP that utilize dowel pins for proper retention of the hinge ring (Ref.-1).
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.
Inspections of the Unit 2 A/D check valves that perform safety related functions revealed another short dowel pin in safety injection valve SI-2-8977, as well as the following additional conditions of non-compliance with the design requirements:
problems with hinge ring locating pin length a.
resulting in the potential to disengege, even
.w if the proper gap between tne hinge ring and dowel pin is maintained, b.
problems with gasket groove dimensions, causing the gap between the bonnet and hinge ring to exceed the 0.090-inch limit c.
one case of the bonnet cover rotated 90 degrees so that the upstream dowel'cannot prevent the upward movement of the locating pin.
On March 30, 1993, a Technical Review Group (TRG)
{
decided to report this event to the NRC in a voluntary Licensee Event Report (LER).
I 93NCRWP'93MMN016 KAB Page 4
of 19 3
NCR: DC043-MM-N016 DRAFT: JUNE 02,1993 On April 2, 1993, an Operability Evaluation (OE) concluded that the Unit 1 A/D check valves of concern did not pose an unreviewed safety question.
The potential for reverse flow is a concern only with respect to a seisnic event.
Any seismic event of 0.2 g or greater ground acceleration requires DCPP to shut down for inspection.
A seismic event of less than 0.2 g would not result in any vertical accelerations at any of the check valves of more than 1.0 g, and hence would not be sufficient to dislodge the hinge ring.
The hinge ring must move upward to allow any of the found conditions of non-compliance with the design to cause back leakage through the valves.
On April 5, 1993, PG&E submitted letter number DAT-016-93 to Westinghouse regarding 10 CFR 21 reportability (Ref. 12)s By April 13, 1993, inspections and required corrections of the Unit 2 valves providing safety related functions were complete, assuring the adequacy of the installation.
D.
Inoperable Structures, Components,oor Systems that Contributed to the Event:
None.
E.
Dates and Approximate Times for Major. Occurrences:
March 10, 1993:
Event / discovery date.
The bonnet dowel pins indicated on-PG&E drawing 663219-434 appeared to be missing from containment spray valve CS-2-9002A.
March 16, 1993:
PG&E discovered that the drawing was an old revision which contained errors.
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.
93NCR%P93MMN016 KAB Page 5
of 19
NCR: DCD 934mi-N016 DRA FT: JUNE 02,1993 March 26, 1993:
Inspections of safety related Unit 2 A/D check valves revealed another short dowel pin on SI-2-8977.
March 30, 1993:
The TRG decided to submit a voluntary LER to report this event to the NRC.
April 5, 1993:
PG&E submitted a letter to Westinghouse regarding 10 CFR 21 reportability.
April 13, 1993:
Inspections and required corrections of the Unit 2 valves-providing safety related functions were complete,-assuring the adequacy of=the inst-llation.
F.
Other Systems or Secondary Functions Affected:
None.
G.
Method of Discovery:
As part of routine inspections of safety related check valves during 2RS, PG&E personnel discovered that the dowel pins were not protruding from the' bonnet as they should have been (Ref. 1).
PG&E personnel later_ discovered in conversation with the valve manufacturer that the manufacturer held an incorrect drawing at the time of valve fabrication, and
""that CS-2-9002A was not mahufactured to th correct ~
design requirements (Ref. 1).
H.
Operator Actions:
None.
I.
Safety System Responses:
None.
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NCR: DC493-MM N016 DRAFT; J(1Nr.w,1993 III.
Cause of the Event A.
Immediate Cause:
Without the correct dowel. fit the potential-uxisted_for-the valve hinge ring.to lift.under. dynamic. conditions (defined by A/D as a seismic event)-and not return.to its required position.
This would result in improper orientation of the val"a disc with the seat _and the.
potential for valve leakage.
B.
Determination of Cause:
Not applicable.
L C.
Root Cause:
l No root cause determination is-required.
The manufacturer supplied equipment-and drawings.that did
~
not comply with the original design requirements.
(
D.
Contributory Cause:
4 Not applicable.
IV.
Analysis of the Event A.
Safety Analysis:
The described condition of bonnet dowel pins of incorrect length creates the potential for valve disk to seat misalignment (Ref. 4) from a seismic evant of 0.2 g ground acceleration or greater.
. Valve disk misalignment would result in reverse' flow leakage, but would not affect the ability of the valve"to> pass' flow in the forward direction.
Reverse flow leakage poses a potent'ial issue with respect _to the ability of the valve.and associated system to perform their design function.
Out of the i
total population of 28 valves of models 2587-5'and-2588-5, 16 (8 per unit) perform safety-related' functions and were. determined to pose a potential operability concern (Ref. 4).
The eight valves of concern are as follows:
CS-9002A/B CS-9011A/B SI-8924 SI-8977 I
93NCRWM93MMN016 KAB Page 7
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I NCR; DC0 93 MM N016 I
DRAFT; JUNE 02,1993 I
CVCS-8440 RCS-8028 The design of the A/D check valve internals.is such that during all conditions of nornal operation (opening and closing), the valve disk is 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 ring to move upward and the locating pin to disengage, resulting.in disk misalignment.
A component which has been discovered to lack full l
seismic qualification may be determined to be operable if all of the following conditions are met (ref. 4) :.
1.
The component will function satisfactorily or i
failure will not prevent a safe shutdown of't'.a Unit following a seismic event (coincident LOCA not considered).
2.
The component will function properly (or will not prevent proper function) for all~ required accident conditions except following the postulated seismic event (LOCA, HELB, abnormal operating condition, etc).
3.
The component will be repaired or replaced at the next Unit outage of sufficient duration.
The described condition is acceptable based upon the following (ref. 4):
1.
M-4, "Eartbquake,"
^
requires that the Unit be. brought to Cold Shutdown in an orderly manner for evaluation of all potentially affected plant equipment for a seismic event with a base mat (ground) acceleration equal to or greater than 0.2g.
All suspect valves are located in lines such that 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.
2.
DCPP Reactor Protection System,' Functional Unit 23, l
" Seismic Trip," is initiated to promptly trip the-reactor in the event of a seismic event greater than 0.35g.
93NCRWF93MMN016.KAs Page 8
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NCR: DCS93-MM N016 DRAFT: JUNE 02,1993 l
l 3.
The probability of a concurrent.(or: closely l
coupled) seismic and LOCA eventLis sufficiently low-that the margin of safety relied upon in the FSAR l
is not significantly altered.
Based on the above-discussion, the col.dition' described l
l in this NCR does: not af f ect the-health and saf ety of.
the public.
l B.
Reportability:
1.
Reviewed under QAP-15.B and determined to be' non-conforming in:accordance with-Section 2il.2.
2.
Reviewed under 10 CFR-50.72'and.10 CFR 50.73 per_.
NUREG 1022 and determined'to be=not reportable'in I
accordance'with 10 CFR'50.72 or.50.73. -However, j
PG&E has-decided to submit voluntary.LER 1-93-004-00 to reportLthe event described in this NCR.
Note:.since this.will'be a voluntary LER, the event l
discovery date is the date on which the TRG decided.
to submit the LER, March.30,-1993.
]
3 heviewed under 10 CFR Part 21 and. determined that I
this problem will not require a 10 CFR[21 report, since it will be reported under'10 CFR 50.72/73.
40 This problem was reported via lut INPO Nuclear i
Network entry, j
1 5.
Reviewed under 10 CFR 50.9 and'determinedJto be not i
l reportable under 10 CFR'50;9 since this event is being reported under.10.CFR 50.73 as'a voluntary LER.
6.
Reviewed under the' criteria of AP C-29;requ' iring the issue and approval?of an OE and determined-that.
an Operability Evaluation (OE) is required.
The OE associated with this'NCR is OE 93-04.
V.
Corrective Actions A.
Immediate Corrective Actions:
1.
All Unit 2 valves. performing a safety related function were returned to the correct design requirements as'necessary during 2R5: (ref. 3,sAE
- 03).
93NCR%P93MMN016 KAB Page
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~ of. 19 l
l NCR: DC&93 MM-N016 DRAFT; JUNE 02,1993 2.
Generate a Field Correction Transmittal (FCT) to document the dimensional requirements and fabrication details that were obtained from Anchor-Darling (A/D) for the inspection and maintenance of the 4" and 8" A/D check valves.
(Ref. PG&E Drawing 663219, Shts. 433 and 434,-respectively)
RESPONSIBILITY:
R. Nanninga.
DEPARTMENT:
MECHANICAL MAINTENANCE TRACKING AR:
- A0299642, AE #07 ECD:
6/30/93
{
STATUS:
COMPLETE B.
Investigative Actions:
1.
Determine if Westinghouse Electric Corporation considers uhemselves to be subject to reporting requirements under 10 CFR 21 for the drawing deficiency identified in this NCR.
RESPONSIBILITY:
R.
Waltos DEPARTMENT:
Mechanical Maintenance TRACKING AR:
- A0299642, AE #01 ECD:
3/26/93 STATUS:
COMPLETE 2.
Submit an INPO Nuclear Network entry informing other plants that the design drawing and associated materials list were revised after the anchor darling check valves were manufactured.
RESPONSIBILITY:
D. Malone DEPARTMENT:
Regulatory Compliance TRACKING AR:
- A0299642, AE #02 ECD:
4/5/93 STATUS:
COMPLETE 3.
Inspect all Unit 2 valves' listed on the POA for bonnet dowel -retaining pin length except for CVCS-2-8279, SFS-2-8763, and SFS-2-8766.
RESPONSIBILITY:
R. Waltos DEPARTMENT:
Mechanical Maintenance TRACKING AR:
- A0299642, AE #03 ECD:
5/30/93 STATUS:
COMPLETE 93NCR%B93MMN016 KAs Page 10 of 19
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J y.
NCR: DCCL934N N016 I
DRAFT: JUNF. 02,1993 '
Note: Please refer to the body of AR A0299642 for 1
the five valves' inadvertently excluded from the inspection list of AE #03.
4.
Inspect valves CVCS-2-8279, SFS-2-8763,-and.SFS-2-:
8766 for bonnet dowel-retaining pin' length as-radiological conditions-permit.
RESPONSIBILITY:
R. '" altos DEPARTMENT:
Mechanical Maintenance TRACKING AR:
- A0299642, AE.#04-ECD:
4/30/94 l
STATUS:
COMPLETE 5.
Inspect.the following Unit i valves (which include valves that perform safety related functions) for compliance with the design requirements.specified correctly in Revision F to drawing 663219-434:
CS-9002A/B; RCS-8020.
CS-9011A/B CVCS-8252A/B/C SI-8924 CVCS-8279 SI-8977 SFS-8763.
CVCS-8440 SFS-8766 l
RESPONSIBILITY:
R. Nanninga DEPAR'INENT:
Mechanical Maintenance TACKING AR:
- A0299642, AE #06
~~
ECD:
5/30/94 STATUS:
ASSIGNED 6.
Prepare and submit voluntary LER 1-93-004-00 to the NRC.
i RESPONSIBILITY:
K. Bruno DEPARTMENT:
Regulatory Compliance TRACKING AR:
- A0299642, AE #08 l
ECD:
6/30/93 i
STATUS:. ASSIGNED C.
Corrective Actions to Prevent Recurrence:-
l t
None required.
D.
Prudent Actions (not required for'NCR' closure)
. Develop a component specific procedure that provides inspection,' disassembly, and reassemblyfdetails-for the 93NCRp93MMN016xAB Page 11 of-19 Y
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NCR; DC091-MM N016 DRAFT: JUNE 02,1993 maintenance of the subject 4" and 8" Anchor-Darling check valves.
RESPONSIBILITY:
R. Nanninga DEPARTMENT:
MECHANICAL MAINTENANCE TRACKING AR:
A0303294 ECD:
2/1/94 l
STATUS:
ROUTED VI.
Additional Information A.
Failed Components:
None.
B.
Previous Similar Events:
NCR DC2-88-MM-N111 discusses the discovery'of reta'ining block stud breakage in Anchor-Darling check valves due to intergranular stress corrosion cracking (as was-later reported in 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.
Similarly, for the current event PG&E has made the necessary corrections to Unit 2 valves to ensure that they are in compliance with the design, and Unit 1 valves will be inspected and corrected as required.
This previous event was reported by PG&E in voluntary LER 2-88-014-00 (ref.
14).
s.-
s:e C.
Operating Experience Review:
1.
NPRDS:
A search of the NPRDS data base found no applicable items.
2.
NRC Information Notices, Bulletins, Generic Letters:
NRC Information Notice 88-85 was issued to report the conditions described above as reported.in LER 2-88-014-00, and'similar conditions found by another utility.
Please see the discussion above regarding NCR DC2-88-MM-N111 (ref. 15).
93NCRw?93MMN016 KAB Page 12 of 19 f
j.'
NCR: DC493-MM-N016 DRAFT: JUNE 02,1993 3.
INPO SOER 86-3, " Check Valve Failures or Degradation," was issued in response to the high number of check valve failures that had been reported to INPO.
As a result of this SOER,-DCPP developed a check valve inspection program, under which the conditions described in this-current NCR were discovered (ref. 16).
D.
Trend Code:
Responsible department: 10C (Manuf acturer/ supplier) ;
cause code: F (Root cause not required).
E.
Corrective Action Tracking:
1.
The tracking action request is A0299642.
2.
Are the corrective actions outage related?
Yes.
F.
Footnotes and Special Comments:
None.
G.
References:
l'.
Initiating Action Request (AR) A0297315.
2.
Drawing 663219-434-4, Revision E.
3.
Tracking AR A0299642.
4.
Operability Evaluation (OE) 93-04.
5.
Telephone records of conversations between PG&E and Anchor Darling, dated March 10, 1993, March 22, 1993, and March 29, 1993.
6.
Summary of surveillance test history for Safety Injection valves SI-8924 and SI-8977, dated March 20, 1993' 7.
Design deviations of Unit 2 Anchor Darling check.
valves discovered during 2R5 inspections-8.
NRC IE Information Notice No. 81-35, " Check Valve Failures," dated December 2, 1981 93NCR%793MMN016XAB Page 13 of 19
e NCR: DC493-MM-N016 DRAFT: JUNE 02.1993 9.
DCPP " Response to December 2, 1931 NRC Information Notice 81-35, ' Check Valve Failures'," dated May 11, 1982
- 10. AR A0303294, prudent action
- 12. Letter number DAT-016-93 from D. Taggart of PG&E to S. McHugh of Westinghouse, dated April 5,
- 1993, regarding 10 CFR 21 responsibility
- 13. Page 2 of a letter dated February 5, 1993, from J.
Hoch, regarding operability considerations relating to a loss of coolant accident and simultaneous seismic event
- 14. Licensee Event Report (LER) 2-88-014-00, transmitted via PG&E Letter DCL-88-281
- 15. NRC Information Notice No..88-85,
" Broken Retaining Block Studs on Anchor-Darling Check Valves"
- 16. INPO SOER 86-3, " Check Valve Failures or Degradation" H.
TRG Meeting Minutes:
On March 22, 1993, the TRG convened and considered the following:
1.
The event description The TRG discussed the discovery of the short dowel pin in containment spray valve CS-2-9002A.
Please refer to part II, " Description of Event."
2.
The prompt operability assessment (POA) l Diablo Canyon has a total of 28 Anchor' Darling check valves that-were manufactured to the erroneous drawing and material list, and which therefore potentially have short dowels.
Out of this total population, the POA identified 16 valves (eight per unit) that pose a potential operability concern, including CS-9002 A/B.
1 L
l 93NCRWP'93MMN016 KAB Page 14 of 19
i NCR: DCCL93-MM N016 DRAFT: JUNE 02,1993 l
l Using the same drawing and procedure that l
identified the short dowels on CS-9002A, l
inspections of these valves have been performed in l
the past and no problems were found.
The POA l
therefore concludes that there is no evidence that the dowels in the other valves of concern are not capable of retaining the-hinge ring during a i
seismic event.
(Ref. 1)
At this point, an Operability Evaluation (OE) will only be needed if a problem is found on another valve identified in the POA as a potential concern.
3.
Reportability l
l It was determined that this event was not reportable under 10 CFR 50.72 or 10 CFR 50.73.
However, this event may-be reportable under 10 CFR 21.
The'TRG decided to request that Westinghouse, the actual vendor of the valves, perform a Part 21 j
investigation.
l 4.
Investigative actions The TRG initiated investigative actions 1 through 4 above (AEs 01 - 04 on AR A0299642).
L The TRG reconvened on March 30,.1993 and considered the following:
1.
Results of A-D check valve inspections to'date At the time of the meeting all of the' remaining Unit 2 check valves of concern had been inspected.
l The most significant finding was the discovery of a bonnet dowel pin shorter than the design ler.gth in safety injection valve SI-2-8977.
The inspections also revealed:
l a.
the potential for the hinge ring locating pin to disengage, even if the proper gap between the hinge: ring and dowel pin is maintained, b.
some valves with the. gap between the body and the bonnet cover out of tolerance, and l
l 9mCRWP93MMN016 KAB Page 15 of 19 l
9 NCR: DCS93-MM-N016 DRAFT: JUNE 02,1993 c.
one valve with the bonnet cover rotated 90 degrees so that the upstream dowel cannot prevent the upward movement of the locating pin.
2.
Operability As a result of the discovery of anther short dowel pin, an Operability Evaluation was initiated (prior to this meeting).
The TRG discussed the Emergency Procedure for seismic events.
DCPP is required to bring'the plant to cold shutdown for inspection /-evaluation following an earthquake with a ground acceleration' of 0.2g or greater.
The probability of a LOCA within this time frame is insignificant.
An earthquake with a ground acceleration of 0.2g or less would result in a vertical acceleration of-1 less than 1.0g at the identified valves.
- Hence, the hinge ring could not move upward and dislodge.
The TRG noted that none of the new discoveries negate the original POA.
3.
Reportability The TRG decided to cubmit a voluntary LER to report this event to the NRC, in order to address 10 CFR l
21 reportability in a timely manner, j
The TRG reconvened on April 13, 1993, Andcons[$ered the following:
1.
10 CFR 21 reportability PG&E sent a letter to Westinghouse dated April 5, 1993, to inform the valve. supplier of the found=
conditions with respect to 10 CFR 21 reportability.
2.
Root cause The TRG determined that the root cause of this event is that the valve supplier provided PG&E with' equipment that didn't comply with the design requirements.
No corrective actions to prevent 93scRWE93MMN0161A8 Page 16 of 19
e NCR: N93 MM N016 DRAFT: JUNE 02,1993 recurrence are required since PG&E is not responsible for this event.
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93scawr9mMN016 KAB Page 17 of 19 j
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NCR: DC093 MM-N016 dun: HAE M.199) 3.
New actions The TRG decided to initiate a new investigative action to ensure that the inspections of the Unit i valves of concern are performed during either 1R6 or a forced outage before IR6.
The TRG agreed on a new immediate corrective action to generate an FCT to ensure that the correct design requirements are included on drawings 663219-433 and 663219-434.
The TRG agreed on a prudent action to develop a component specific procedure for_ maintenance of 4" and 8" Anchor Darling check valves.
4.
2R5 inspection results The TRG reviewed the problems that were found on the Unit 2 A/D check valves.
Every 4" valve inspected on Unit 2 had a problem.
There were three categories of problems: (1) incorrect bonnet dowel length, (2) hinge ring pins with the potential to disengage as a result of a seismic event, and (3) incorrect gasket crush.
The TRG reconvened on April 27, 1993 and reviewed and edited the draft of voluntary LER 1-93-006.
The TRG considered whether this event is generic to check valves.
The TRG agreed that this is an isolated case.
There was nothing that PG&E could have done to Frevent the problem with the vendor drawing.
For the purpose of the LER, the TRG decided that the event date was the date on which the-TRG decided to submit a voluntary LER (March-30).
The TRG reconvened on May 6, 1993 to review and edit the NCR and LER write-ups.
The TRG will reconvene on May 18 to review the draft LER.
The TRG reconvened on May 18, 1993 to review the draft t
LER, and will reconvene on June 2, 1993 to sign off this NCR.
The TRG reconvened on June 2, 1993 to sign off this NCR.
The wording of the non-conformance description 93NCRW93MMN016 KAB Page 18 of 19 I
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NCR: DCS93-MU MN6 DRAFT: JUNE 02,1993 l
was changed on the original NCR, and an NCR closure date of June 15, 1994, was assigned.
The TRG reviewed this NCR write-up and made minor editorial changes.
The TRG extended the submittal due date for voluntary LER 1-93-004-00 to June 30, 1993.
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Remarks:
l None.
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