ML20062J978
| ML20062J978 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 08/18/1993 |
| From: | Rueger G PACIFIC GAS & ELECTRIC CO. |
| To: | |
| References | |
| OLA-2-I-MFP-050, OLA-2-I-MFP-50, NUDOCS 9311190389 | |
| Download: ML20062J978 (9) | |
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-l Pacific Gas and Electric Company 77 Beale Street. Room 1451 Gregory M. Rueger P0 Box 770000 Senior Vice President and SanFrancisco CA941MCKLILD GeneralManager 415!973-4664
'Jt NRC Nuclear Power Generation Fax 415/973-2313
'93 0"I 28)91 # M d f 5 b April 5, 1993 b
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PG&E Letter No. DCL-93-077 M:'".
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U.S. Nuclear Regulatory Commission i
ATTN: Document Control Desk Washington, D.C.
20555 1
Re: Docket No. 50-323, OL-DPR-82 i
Diablo Canyon Unit 2 Licensee Event Report 2-93-002-00 Entry Into Technical Specification 3.0.3 Due to Auxiliary Building Ventilation System Inoperability Caused by Inadequate Work.
Instructions Gentlemen:
Pursuant to 10 CFR 50.73(a)(2)(1)(B), PG&E is submitting the enclosed 3
Licensee Event Report (LER) regarding entry into Technical Specification 3.0.3 due to the auxiliary building ventilation system inoperability caused by inadequate work instructions.
The root cause of this event will be provided in a supplement to this LER.
This event has in no way affected the health and safety of the public.
Sincerely,
)
f Ilnw AAu p Gregory M. Rueger cc: Ann P. Hodgdon
-a-John B. Martin i
Mary H. Miller Sheri R. Peterson CPUC Diablo Distribution INP0 DC2-93-MM-N012 fiUCLIA2 R!GULAfoRY CDMMISSloN w SM S -tit _ ou,, r
'nFP 50 Enclosure re,2 no 1106S/85K/PGD/2246
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5 LICENSEE EVENT REPORT (LER) e F ACIUTv N AME Ol DOCEFT NUMBUI(16 PAGE (3) 1 DIABLO CANYON UNIT 2 0l5l0l0l0l3l2l3 1l'l 8 ENTRY INTO TECHNICAL SPECIFICATION 3.0.3 DUE 10 AUXILIARY BUILDING VENTILATION nru ia SYSTEM INOPERABILITY CAUSED BY INADEQUATE WORK INSTRUCTIONS i
EVENT DATE (Gl LER NMM (06 REPORT DATE (73 OTHEa FACILITIES INv0LVED (8) l uom par vn vn eso nat REvisoN won oAv vn pocx1T NuussR ts:
y 0
5 0
0 0
03 04 93 93 0l0l2 0l0 04 05 93 0
5 0
0 0
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THIS REPORT 15 $USMITTED PVR5uANT to THE REQUIREMENTS OF 30 CFRa (13) 1 i
Lr7tY x 10 crR 50.73(a H 2HiF B) l l 5l 0
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OTHER -
(Specify in Abstract below and in text, NRC Form 366A)
UCENsu CONT ACT FOn T6et L94 O f t fftIpHONE NUMBfR DAVID P. SISK, SENIOR REGULATORY COMPLIANCE ENGINEER
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l 805 545-4420 l
COMPLETE ONE UNE FOR EACH COuPONENT FAILURE DESCftBED IN THis REPORT (131 CAUSE System COMPONENT MAN AC.
R PO E
CAUSE SYSTEM COMPONEh?
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III III I
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III III suPPuurntat REPORT ExPtcTEn ties D^'
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EXPECTED SUBMI$$ ION IXl YES (if yes, conplete EXPECTED SUBMISSION DATE) l l No 07 30 93 A851RACT (46)
Or. March 4, 1993, at 1242 PST, with Unit 2 in Mode 1 (Power Operation) at 50 percent power, Technical Specification (TS) 3.7.6.1 was not met and TS 3.0.3 was entered.
One train of the auxiliary building ventilation system (ABVS) was made inoperable by the closure or a manual damper during the perf.: nance of a preventive maintenance
~~
activity.
SinceThe other train of the ABVS was already inoperable for th'is maintenance activity, TS 3.0.3 was entered.
1 On March 4, 1993, at 1257 PST, PG&E operators instructed maintenance personnel to i
ieopen the manual dampers that had been closed. One train of the ABVS air flow was reestablished and the TS 3.0.3 action statement was exited.
The preliminary root cause for this event was determined to be inadequate work instructions. Additional potential root causes and corrective actions are under investigation and results of these investigative actions will be provided in a supplement to this LER.
Il06S/85K 1
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LICENSEE EVENT REPORT (LER) TEXT CONTINUATION
.. _r 0l0l2 0l0 2 l"l8 DIABLO CANYON UNIT 2 0l5l0l0l013l2l3 93
[
I TERT (17)
I.
Plant Conditions Unit 2 was in Mode 1 (Power Operation) at 50 percent power.
II. Descriotion of Event i
A.
Summary:
On March 4, 1993, at 1242 PST, with Unit 2 in Mode 1 (Power Operation) at 50 percent power, Technical Specification (TS) 3.7.6.1 was not met and TS 3.0.3 was entered. One train of the auxiliary building ventilation system (ABVS) was made inoperable by the closure of a manual Since the damper (VF)(DMP) during a preventive mair.tenance activity.
other train of the ABVS was already inoperable for this maintenance activity, TS 3.0.3 was entered.
On March 4, 1993, at 1257 PST, PG&E operators instructed PG&E maintenance personnel to reopen the manual dampers.
One train of the l
ABVS air flow was reestablished and the TS 3.0.3 action statement was exited.
l 8.
Background:
Each unit has two ventilation trains. The ABVS main function is to maintain the ambient temperature around engineered safety feature (ESF) equipment within acceptable limits and to filter ' exhausted air to minimize the amount of radiation released during accident' conditions.
The ABVS has three modes of operation. The first mode is the building only ventilation mode, with one supply and one exhaust fan (NF)(VF)(FAN) l in operation.
The seconu mode is the building and safeguards mode, with l
two supply and two exhaust fans in operation. -The third mode is the safeguards mode, with one supply and one filtered exhaust fan in l
operation. A safety injection (SI) "S" signal places the ABVS in the safeguards mode and redirects the flow through the charcoal absorber banks (NF)(VF)(ADS).
l TS 3.7.6.1 requires that two auxiliary building (NF) safeguards air filtration system exhaust trains with one common high efficiency particulate air (HEPA) filter (NF)(VF)(FLT)-and charcoal absorber bank and at least two exhaust fans be operable in Modes 1 through 4 (Hot Shutdown).
C.
Event Description.
\\
On March 2,1993, Mechanical Maintenance personnel were preparing to perform a preventive maintenance activity to clean a flow element (FE-5016) (VF)(FI) associated with the Unit 2 ABVS. The clearance 1106S/85K c
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E LICENSEE EVENT REPORT (LER) TEXT CONTINUATION 5
i FACILITY NAMC (I)
CoCEET NUMh[R (2).
L(R NUMBER 5)
PAGE (3)'
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DIABLO CANYON UNIT 2 0l5l0l0l0l3l2l3 93 010l2 0l0 3 l 'l 8 TEXT (17) alignment for this maintenance activity placed the ABVS in safeguards mode with an SI "S" signal, which automatically. opens' Dampers 8A, 8B,.
lA, and IB and closes Dampers 2A, 28, 4A and 4B (see drawing on Page 8).
This maintenance activity had been previously performed successfully using the same clearance alignment.
The work order that implemented the maintenance activity required closing the dampers, but did not specifically identify which dampers.
The alignment of this system enecifies routing of flow through the charcoal filters,. which requires that painting and welding restrictions be imposed in the auxiliary building for the duration of the clearance.
On March 3, 1993, a request was made to impose welding and painting restrictions on the ABVS to be effective on March 4, 1993.
These restrictions would have impacted on-going outage work. An alternate clearance was researched between System Engineering and the Operations coordinator and a new clearance was issued.
This new clearance left the flow through the charcoal filters isolated.
Dampers IA,.1B,~8A and.8B remained closed. The flow path using Fan 2E-1.was through Dampers 2A and 2B and Manual Dampers (MDs) MD-3, MD-5A and MD-5B.. Dampers 4A and 4B remained closed and Fan 2E-2 disabled in order to perform the maintenance activity. The new clearance eliminated the requirement to l
initiate the "S" signal.
On March 4,1993, Mechanical Maintenance personnel requested Operations.
approval to start work. The Unit 2 Shift Foreman determined that the work instructions were not specific regarding which dampers were required to be closed. The Mechanical Maintenance work:.a discussed the damper closure requirement with a maintenance engineer who previously; had performed this activity and who indicated that MD-SA and MD-5B were required to be closed. The workers reported to the Shift Foreman and identified that MD-5A and MD-5B were required to be closed.. The Shift Foreman agreed to the closure of those two dampers since this action maintained a flow path through MD-3.
The maintenance workers were allowed to begin work and began so by closing MD-5A'and MD-58.
In order to enter the ducting that contained the FE-5016, an access hatch was required to be removed from the plenum in which the dampers were located.
There was a differential pressure across the hatch.
This prevented the workers from opening the hatch.
Work was suspended and the Mechanical Maintenance foreman was contacted. The foreman noted that MD-3 on an upper elevation of the plenum was open. Although the n
maintenance personnel had informed the Unit 2 Shift Foreman that they were only going to close MD-5A and MD-58, the. work order. instructions' that required closure of the dampers were not specific as to which dampers to close.
The Mechanical Maintenance foremar, determined it was acceptable to close MD-3 since the work order instructions were not specific regarding the closure of dampers.
This activity, previously performed under different alignment conditions, required MD-3 to be closed.
When the Mechanical Maintenance foreman moved MD-3, a position 1106S/85K
t LICENSEE EVENT REPORT (LER) TEXT CONTINUATION m
noe m tragra
= cur oea m ucran w m DIABLO CANYON UNIT 2 0l5l0l0l0l3l2l3 93,- 0l0l2 0l0 4 l 'l 8 TE11 (17) switch activated and signaled the ABVS control logic to shut down the only ABVS operable fan (2E-1).
Fan 2E-2 was already inoperable for this maintenance activity.
Since both Unit 2 ABVS fans were inoperable, the requirements of TS 3.7.6.1 were not met and TS 3.0.3 was entered. One train of the ABVS was restored within 15 minutes. As a result, the requirements of TS.3.7.6.1 were met and TS 3.0.3 was exited.
D.
Inoperable Structures, Components, or Systems'that Contributed to the Event:
None.
E.
Dates and Aporoximate Times for Major Occurrences:
l.
March 4, 1993, at 1242 PST:
Event / Discovery date.
The only operable ABVS train B was made i
l inoperable by the closure of dampers for Fans 2E-1 and 2E-2.
This resulted in the violation of f
TS 3.7.6.1 and entry into TS 3.0.3.
l 3.
March 4, 1993, at 1257 PST:
TS 3.7.6.1 requirements were met and TS 3.0.3 was exited when one train of the ABVS was restored to operability.
I l
F.
Other Systems or Secondary Functions Affected:
1 None.
~
G.
Method of Discovery:
The event was immediately apparent to plant operators due to alarms and indications received in the control room.
I H.
Operator Actions:
PG&E operators instructed maintenance personnel to reopen MD-5A, MD-5B, l
and MD-3 and restarted Fan 2E-1, which reestablished air flow through' l
l one train of the ABVS such that the TS 3.0.3 action statement was I
exited.
I.
Safety System Responses:
None required.
1106S/85K i
a j.
g LICENSEE EVENT REPORT (LER) TEXT CONTINUATION 5
l.
FCCILITY NAME (1)
Docatt MUM 8(4 (2)
LER NUMStB in)
D&fsf (3) I j
3
~3 DIABLO CANYON UNIT 2 0l5l0l0l0l3l2l3 93
- 0l0l2 0l0 5 l 'l 8-l III. Cause of the Event A.
Immediate Cause:
~
The immediate cause of this event was the inadvertent trip of the'ABVS Exhaust Fan 2E-1 due to a damper manipulation.
B.
Root Cause:
The preliminary root cause for this event was determined to be inadequate work instructions. The work order did not state which dampers should be closed and which dampers should be left open.- The alternate clearance was not sufficient to allow the access hatch cover-to be removed.
The Technical Review Group (TRG) is investigating additional potentia root causes and the results of these investigative actions will_.be reported in a supplemental LER.
H C.
Contributory Cause:
J Potential contributory causes which led to the work order and clearances not containing enough information to perform this' task are being 3
investigated.
The results of this investigation will-be reported in a revision to this LER.
IV.
Analysis of the Event l
The primary safety function of the ABVS is to maintain the ambient l
temper-%re around the ESF equipment within acceptable limits and filter air j
following a. loss-of-coolant accident (LOCA) during the post-LOCA
{
recirculation phase.
The FSAR Update Chapter 15 analyzes the offsite exposures from post-LOCA circulation loop leakage in the auxiliary building.
Two cases are analyzed:
large leakage and long-term small leakage.
The large' leakage case-assumes a i
single passive failure of a residual heat removal pump seal (BP)-(SEAL) and gives credit for filtration of radioactivity bylthe ABVS. An SI signal aligns the ABVS to the "S" signal mode.
The operators manually depress the reset control to start Fan E-1.
Therefore, there is no effect on the FSAR' Update Chapter 15 analysis.
For the small leakage case, no credit was given in the FSAR Update for the charcoal filter. The control room dose has not been explicitly analyzed.
A review of existing analysis and timing indicates th_at 10 CFR 50, Appendix A, General Design Criterion 19 limit will not be exceeded within the time required to restore the system operations (within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />)..
I l06S/85K l
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION DOCKET NUMBER (2)
LIR NUMetR 46)
PAM (3)
- rocn!TV NAME (3) vsu secuen a svmon DIABLO CANYON UNIT 2 0l5l0l0l0l3l2l3 93 0l0l2 0l0 6 l"l8 ttaf (p)
Failure of the ABVS does not immediately jeopardize the operability of any safety-related equipment. A review of room heatup curves indicates that 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is available before any safety-related equipment could adversely be affected.
Emergency Procedure (EP) E-0, " Reactor Trip or Safety Injection,"
has been previously revised to provide the operators with the necessary guidance to recover the ABVS.
Based on the guidance provided in EP E-0 and the fact that EP E-0 is the first procedure implemented following a reactor trip for SI, the operators will promptly restore the ABVS to mitigate the consequences of an accident and provide cooling to the ESF equipment.
In this event, MD-5A, MD-5B, and MD-3 were reopened and the air flow of the ABVS was reestablished within 15 minutes of the initiation of the event.
Therefore, it has been demonstrated that the ABVS can be restored in much less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
In addition, since the safety functions of the ABVS would be accomplished, this event did not adversely the health and safety of the public.
V.
Corrective Actions A.
Immediate Corrective Actions:
MD-5A, MD-5B and MD-3 were reopened. The air flow was reestablished through Fan 2E-1 fan and TS 3.0.3 action statement was exited.
B.
Corrective Actions to Prevent Recurrence:
The TRG is investigating the root causes of this-event and the applicable corrective actions. The results of this investigation will be provided in a supplement to this LER.
VI. Additional Information A.
Failed Components:
None.
B.
Previous Similar Events:
LER 1-92-011 Entry Into Technical Specification 3.0.3 Because of Auxiliary Building Ventilation System Inoperability Due to Noncognitive Personnel Error On December 17,1992, TS 3.7.6.1 was not met for the auxiliary building when Exhaust Fan E-2 and Supply Fan S-34 were secured for maintenance' and testing and the ABVS entered the 7-day allowed outage time of TS 3.7.6.1 action b.
As a result, TS 3.0.3 was entered.
On December 17, 1992, at 2227 PST, TS 3.0.3 was exited when a control room operator restarted Fan E-1.
The root cause was determined to be personnel error, noncognitive, in that licensed 1106S/85K W-A
i LICENSEE EVENT REPORT (LER) TEXT CONTINUATION i
FOCILITV NAME (3)
DOCKET NUMSER (f)
LfD NUMSER
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operators knew that resetting the "S" signal would reposition the i
dampers, but did not know that Exhaust Fan E-1 would shut down and restart while the dampers repositioned.
Corrective actions include the revision of applicable procedures to include precautions when maintenance verification testing is being performed on the applicable ABVS dampers. The corrective actions for the previous event did not prevent this event.
The root causes of the present event are still under investigation and the corrective actions to prevent recurrence have not yet been determined.
LER l-92-012 Entry Into Technical Specification 3.0.3 Due to Auxiliary Building Ventilation System Inoperability Resulting from a Single Failure On August 8, 1992, TS 3.7.6.1 was not met for the auxiliary building when both ventilation trains failed for approximately 38 minutes.
As a result, TS 3.0.3 was entered.
On August II, 1992, a preliminary engineering assessment of the ABVS design determined that a loss of 125 VDC sensor power (JG)(EJ) to one train of the ventilation system could cause a loss of the fans in the other train, resulting in a complete loss of the ABVS.
Consequently, the ABVS appeared susceptible to a common mode failure and therefore might be unable to mitigate the consequences of an accident simultaneously with a single failure.
The root cause of this event was personnel error, cognitive, in that the responsible engineer for the addition of flow switches (in the mid-1970s) did not eviate the effect on the control logic of a loss of DC power as part of the design change failure modes and effects analysis.
The corrective action for this previous LER is to implement a design change to eliminate the potential for an ABVS common mode failure.
The corrective actions for this previous LER would not have prevented the current event since the current event does not involve a loss of 125 VDC sensor power to the ABVS.
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