ML20237A120
| ML20237A120 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 08/05/1998 |
| From: | Head S HOUSTON LIGHTING & POWER CO. |
| To: | |
| Shared Package | |
| ML20237A107 | List: |
| References | |
| LER-98-S01, LER-98-S1, NUDOCS 9808130108 | |
| Download: ML20237A120 (7) | |
Text
'
NRC FwR2 366 U.S. NUCLEAR RE1ULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 E4sl EXPIRES 04/30/98 ISilMail8 sengtN Pla RESPeget to ceGPLY Wilt flN5 IMNhatest meesNATien j
estuenegn: se.e sat narents tasseus tunuse ma mesapenstes "n"anEne suasu unn" attn "penEn'e"s 'm"e 'asEmannetut LICENSEE EVENT REPORT (LER) a s
emmen 174 reet mA suotua nasutatear commessen, wasmeston, se resss-(See reverse for required nurnber of ese te m,s,r,aru,wsan g g,,yJtetlame n t e t er ge g gT gugg digits / characters for each block)
FActuTV NAME (1)
DOCKET NUMBER (2)
PAGE (3)
South Texas Unit 1 05000 498 1 of 7 mLE(9 Loss Of Power Supply to the Security System EVENT DATE (5)
LER NUMBER (6)
REPORT DATE (7) oTHER FACILITIES INVOLVED (8)
MONTH DAY YEAR YEAR SE AL REV MONTH DAY YEAR FACIUTY NAME DOCKET NUMBER South Texas Unit 2 05000 499 07 07 98 98 -
S01 00 08 G4 98 FAGIUTY NAME DOCKET NUMBER 05000 OPERATING
]
THIS REPORT IS SLBMirTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 5: (Check one or more) (11)
MODE (9) 20.2201(b) 20.2203(a)(2)(v) 50.73(a)(2)(i) 50.73(a)(2)(viii) 20.2203(a)(1) 20.2203(a)(3)(l) 50.73(a)(2)(li) 50.73(a)(2)(x)
POWER 100 LEVEL (10) 20.2203(a)(2)(i) 20.2203(a)(3)(ii) 50.73(a)(2)(iii)
X 73.71 m gg@ (
20.2203(a)(2)(ll) 20.2203(a)(4) 50.73(a)(2)(lv)
OTHER h
yf" 20.2203(a)(2)(iii) 50.36(c)(1) 50.73(a)(2)(v) gin Abs below or p
20.2203(a)(2)(iv) 50.36(c)(2) 50.73(a)(2)(vii)
LICENUEE CONTACT FOR THIS LEll(12)
NAME TELEPHONE NUMBER (loclude Area Gode)
Scott M. Head -Sr. Consulting Engineer (512)972-7136 COMPLETE ONE LINE FOR EACH COMPdNENT FAILURE DE SCRIBED IN THIS REPORT (13)
~
CAUSE SYSTEM COMPONENT MANUFACTURER R
T E
GAUSE SYSTEM COMPONENT MANUFACTURER REPORTA E S JPPLEMENTA. REPORT EXPLCTED (14)
EXP ECTED MONTH DAY YEAR SUBMISSION DATE (15)
YES
)(
NO (If yes, complete EXPECTED SUBMISSION DATE).
AB STRACT (Limit to 1400 spaces,i.e., approximately 15 single-spaced typewntten lines) (16)
On July 7,1998, Units I and 2 were in Mode 1 at 100% power. At approximately 1433 hours0.0166 days <br />0.398 hours <br />0.00237 weeks <br />5.452565e-4 months <br />, power to the 20 KVA inverter was interrupted which resulted in a loss of power to the security computer system and associated devices. Compensatory measures for a total security system failure were initiated and all required security positions were posted. Power was restored to the security system within minutes. The cause of this event was the inverter switching to the alternate power source due to failure of the Static Switch Board. The Static Switch l
Board has since been replaced. The root cause of the event was that the Root Cause Analysis for a similar event that occurred in July,1997 did not identify a material condition problem with the inverter. Current corrective i
actions include review oflessons learned with Root Cause Analysis investigators and Security Personnel, training, j
procedure revision, drawing revision, revision of Post Order prioritization, and planned participation of Security
)
Personnel in appropriate Control Room briefings.
9808130108 980805 PDR ADOCK 05000498 S
PM l
NRC FORM 366 (4 95) wpinlinre-ap\\r:r-98ber98s01. doc STI3%:lll6
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACluTY NAME (1) l DOCKET LEH NUM ?ER (6)
PAGE (3)
South Texas Unit 1 L
05000 498
%?J5ff Ma@
2 of 7 ~
98 - S01 00 TEXT (If more space is required, use additional copies ofNRC Form 366A) (17) l
\\
DESCRIPTION OFRENI:
On July 7,1998, Units 1 and 2 were in Mode 1 at 100% power. At approximately 1433 hours0.0166 days <br />0.398 hours <br />0.00237 weeks <br />5.452565e-4 months <br />, power to the 20 KVA inverter was interrupted which resulted in a loss of power to the security computer system and associated devices.
The 20 KVA security UPS is a 120Vac single phase uninterruptible power supply. The system consists of a rectifier / charger, a DC-AC power inverter, an external battery bank, a static switch, and a manual bypass switch. The normal and bypass power sources are fed from non-class lE 480 Vac MCC 12K3 which is backed
(
up by the lighting diesel generator. The security loads are normally fed from the inverter via the static switch and a manual bypass switch. In the event of a loss of the nonnal AC power source, the UPS batteries will supply the inverter to maintain continuity of power to security loads for at least 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> or until the lighting diesel generator starts and powers MCC 12K3. In the event of an inverter failure, a low inverter output j
voltage, an overload or load faults, the load will be transferred from the inverter to the bypass source.
On July 7,1998, at approximately 1424 hours0.0165 days <br />0.396 hours <br />0.00235 weeks <br />5.41832e-4 months <br />, maintenance was being performed for load center bre'aker 12L cubicle 3D (supply to MCC 12K3); an overhaul of the breaker. At 1424, the normal supply breaker on load center 12L was opened resulting in an expected dead bus. At this time, alarms from the 20 KVA battery l
charger,15 KVA battery charger, and the 12L normal supply breaker were received in the security alarm l
stations. The battery charger alarms indicated that power to the battery chargers was lost and the batteries j
were supplying the inverter loads. At 142.5, the lighting diesel generator output breaker was closed to energize l
the 12K3 bus appropriately clearing the alarms (20 KVA battery charger and 15KVA battery charger). Four j
seconds after the output breaker closed, the Central Alarm Station and the Secondary Alarm Station received l
an unexpected 20 KVA UPS TS BYPASS alarm. Patrol offica were dispatched to verify / investigate alarms on the 15 KVA,20 KVA battery chargers, and the alarm on e acurity inverter. In addition, at 1432 hours0.0166 days <br />0.398 hours <br />0.00237 weeks <br />5.44876e-4 months <br />, a report was received that the 'in sync' and ' alternate source' lights were on.
1 As part of the maintenance activity, at 1432, the normal supply breaker located in cubic!e 3D on 12L load j
center was placed in the ' Test' position and manually cycled to the ' closed' position. This caused the output I
breaker on the lighting diesel generator to open. The opening of the output breaker resulted in a loss of power to security loads on the 20 KVA inverter due to the 20 KVA inverter being in bypass (no battery backup).
Compensatory measures were implemented for a Total System Failure and all required Security positions were j
posted.
At 1434, the power was restored to MCC 12K3 and the security battery charger alarms (20KVA and 15KVA) returned to normal. At 1441 hours0.0167 days <br />0.4 hours <br />0.00238 weeks <br />5.483005e-4 months <br />, the security computer system was operational. At 1608, the 20 KVA l
inverter was restored to the normal lineup. At 2148, opersility testing was completed and system failure l
positions were secured.
i wp\\nlinrc-ap\\ser-98%cr98s01 doc STI 30681116 i
t
alt NHN rA81 M-nut ATORY er""MMN LICENSEE EVENT REl' ORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUM ER (6)
PAGE (3) l South Texas Unit 1 05000 498 YEAR Ugj0TR 3
of 7
98 S01 00 TEXT (Ifmore space is required, use additional copies ofNRC Form 366A) (17)
DESCRIPTION OF EVENT: (continucdj Prior to commencement of the work activity, a shift briefing was conducted with the security force. The briefing included notification that maintenance activities would be taking place on the security power supply normal supply breaker. At approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, security supervisors were notified when the maintenance
. activity was about to commence; however, this information was not effectively communicated to the alarm stations. As a result, when the 12L Normal Supply Breaker,15KVA Battery Charger, and 20KVA Battery
' Charger alarms were received, they were treated as unexpected alarms.
Upon receipt of the alarms, a system ' post order' (written instruction electronically tied to an alarm point) was utilized to aid in the appropriate alarm response. The post order steps were:
assess situation...is testing in progress?
o Dispatch a S/O to door 1M4149.
o Immediately notify supervision / test coordinator (if testing in progress).
o Acknowledge alarm.
o Await response /further instructions.
o Clear alarm when appropriate.
o Approximately forty (40) seconds after receipt of the first alarms and while accessing the associated post I
order:;, the 20KVA UPS TS ON BYPASS alarm was received. All alarms were cddressed in order of receipt.
Four (4) minutes after receipt of the first alarm the Security Force Supervisor was informed of the alarms. As the supervisor was attempting to assess the situation, the total lors of power occurred. No alarm notification l
was made to the Unit 1 Control Room.'
l During this event, the static switch transferred to bypass inappropriately. In subsequent troubleshooting, a problem was identified with the voltage sensing circuitry when a transfer to the alternate source occurred when a component on the Static Switch Board was mechanically agitated. The Static Switch Board has been replaced.
l I
The opening of the lighting diesel generator output breaker during the cycling of the normal supply breaker was
. unexpected. Investigation revealed that the elementary drawing for the lighting diesel generator output breaker identifies the function of the cell switches that interlocked with the normal supply breaker (trip, close permissive, etc). liowever, the normal supply breaker drawing does not contain this information.
The Control Room staff was unaware of previous inverter inadvertent transfer issues. Therefore, this eventuality was not planned for nor discussed during the prejob briefing.
wpinhnreapWr-98%:r98s01 Ar STI 30681116
~==
U.S. NUCLEAR REGULA70RYIQMMISSION LICENSEE EE.NT REPORT (LER)
TEXT CONTINUKfION FACILifY NAME (1)
DOCKER LER NUMBER (6)
PA' E (3) f South Texas Unit 1 05000 498 TUBTa" "M,M 4
of 7
98 - S01 --
00 TEXT (Ifmore space is required, use additional copies ofNRC Form 366A) (17)
DESCRWflON OF EVEF-(cnndamell)
A similar event occurrm on July 21,1997 (SER 97-S02). The investigation of SER 97-S02 centered around the conditions which preceded the loss of power. Ti e investigation concluded that the security loads were transferred to bypass power during the time in which the load on the load banks of the lighting diesel generator was being increased. Subsequent review and analysis of the diesel generator single line and UPS schematics drawings revealed that there should be no correlation between the diesel generator loading and the load transfer of the inverter. In addition, the investigation considered several other abnormal conditions that could cause the inverter to transfer the loads to bypass source.
The investigation concluded no specific evidence could be found which would identify the exact cause of the load transfer; the apparent cause was believed to be attributed to a transient or load spike experienced by the inverter. This conclusion was arrived at based 2pon the process of elimination and through discussions with the UPS vendor. Since the inverter did not experience a loss of an inverter square wave, a loss or deterioration of the inverter output voltage, a load fault or an overload, the only remaining condition that could initiate a transfer of the load to the bypass source is if there was a transient or load spike on the inverter load that caused the static switch to sense an overcurrent condition and initiate the transfer. It was also determined that the cause of the load transfer was not associated with the load increase on the lighting diesel generator even though the transfer ofinverter loads and the load increase on the diesel generator took place at approximately the same
, time.
On September 26,1997, an unexpected transfer of the 20KVA static switch occurred. The transfer occurred at approximately the same time as the stanup of a reactor coolant pump. This event was documented in Condition Report 97-15629 with an action to perform troubleshooting on the inverter. This event prompted additional attention to be directed at the inverter. On October 23,1997, the inverter vendor was onsite and troubleshooting of the inverter was initiated. This troubleshooting evolution was terminated when problems developed with the lighting diesel generator. Troubleshooting was re-scheduled for July,1998. This schedule appeared appropriate in light of the corrective actions implemented from the July,1997 event. It was believed that those actions would suffice as barriers to preclude loss of power recurrence.
CAUSE OF Ti1E EVEN_T:
The initiating cause of this event was the inverter switching to the alternate power source due t intermittent failure of the Static Switch Board. The root cause of the event was that the Root Cause Analysis of the July, 1997 event did not identify a material condition issue with the invener. Contributing Causes identified were:
an incorrect prioritization c'the Security System Post Order action steps, o
The prejob briefing for the security alarm station operators was madequate due to the lack of specific e
l information regarding work start time and information regarding the expected alarms / responses to work activities, and an unexpected opening of the lighting diesel output breaker.
o wpinthap\\ser-98ber98x01.dce STl 30681116
- run- --
UA paart 8AR RFalH ATORY CC" dini 14481 LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUM ER (6) pat E (3)
South Texas Unit 1 05000 498 MR sgggyR
,fu EN 5
of 7
98 - S01 -
00 TEXT (If more space is required, use additional copies ofNRC Form 366A) (17)
ANALYSIS OF EVENT:
Tt.is event is reportable per 10CFR73.71(b)(1) as described in Regulatory Guide 5.62 paragraph 2.2.20. The event is significant because the compensatory measures required by the Physical Security Plan during the loss of all AC power supply to security systems had to be taken CQPRECTIVE ACTIOb:
The following corrective actions have been or will be taken as a result of this event:
1.
Troubleshooting of the inverter identified a problem with the Static Switch Board. The Static Switch Board has been replaced.
2.
Alarm Station Operators and supervisors were briefed on the event and it was communicated that any future receipt of the 15/20KVA Bypass alarm would be immediately communicated to the Unit 1 Control Room via telephone or radio.
3.
Security Post Orders for the 15KVA and 20KVA Inverter have been revised to properly prioritize the action Steps to ensure prompt notification to the Control Room.
4.
Security Post Orders related to other security power supply equipment will be reviewed to determine if revision is required. This will be completed by August 6,1998.
5.
Security personnel will participate in future Control Room prejob briefings and specific information regarding work / test activities will be provided to the alarm station operators. This management expectation will be communicated to all Security Force Supervisors and staff. This will be completed by
. August 6,1998.
6.
Review event and lessons learned with security alarm station operators. This will be completed by August 27,1998.
7.
Revise appropriate drawing (s) to add addihonal i..hrmation regarding the lighting diesel interlock. This will be completed by December 31.
8.
The results of this investigation and the leswns learned on Root Cause Analysis will be communicated to all Root Cause Analysis investigation;. This will be completed by September 15,1998.
wpinlinrc-apkr-98W,98s01.&s ST130681116 -
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET
_ LER NUMBER (6)
PAGE (3)
South Texas Unit !
05000 498 "l *Ede'if "ffs$
6 of 7
98 - S01 -
00 TEXT (ifmore space is required, use additional copies ofNRC Form 366A) (17)
ADDITIONAL INFORMATION:
A review of industry events and Equipment Performance & Information Exchanges (EPIX) report for inverters indicated that there were several instances in which the inverter load transferred to the alternate source.
However, these transfers were not as a result of a Static Switch Board intermittent operation.
During the investigation, it was discovered that plant procedure OPOP02-DB-0004, " Emergency Lighting Diesel Generator" was not revised to include cautions about verifying the inverter on the normal power source prior to switching the lighting diesel generator when plant procedure OPOP07-DB-0004, " Lighting Diesel Generator Performance Test", was revised in response to the last inadvertent loss of the 12K3 bus. Had this present event proceeded beyond the unexpected opening of the lighting diesel output breaker, the lack of this barrier would have led to a loss of power event. This procedure has since been revised to include the above cautions.
As a result of this investigation, it was determined that information on previous inverter problems was not effectively shared with Operations staff. The events discussed in this event will be included in lessons learned training during licensed operator requalification. This will be completed by February 25,1999.
There has been one Security Event Report submitted in the last three years by South Texas Project to the Nuclear Regulatory Commission for loss of power to tiie security system: SER 97-S02 " Loss of Power to the Security System".
\\
i 1
wpinNac-ap\\ner-9ther98s01. doc ST130681116 l
U S NUCLEAR REGULATORgMMI51(N_
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACluTY NAME (1)
DOCKET LER NUM J ER (6)
PA* E (3)
South Texas Unit 1 05000 498
"#deTn" "efu"$
7 of 7
98 - S01 -
00 TEXT (If more space is required, use additional copies ofNRC Form 366A) (17)
SIMPLIFIED LIGHTING DG & 20 KVA UPS SCHEMATIC LC 12L
)
MCC12K3 ALT SOURCE NORMAL S01URCE 480 VAC
=_
)
BATTERY RECT / CHARGER 125VDC
)
f*_
480/120 VAC
)= = d==
)
n TEST l
l LOAD INVERTER PANEL l BANKS
)
)
A H
STATIC TRANSFER a
SWITCH Q
LTG DG H
MANUAL BYPASS SWITCH CDl02104A DISTRIBUTION PANEL (SEC. LOADS) i wp\\nl\\nrc-ap\\ser 98Ver98s01 Aw STI 30681116