ML20211G766
| ML20211G766 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 09/30/1997 |
| From: | Kennedy J NRC (Affiliation Not Assigned) |
| To: | NRC (Affiliation Not Assigned) |
| References | |
| NUDOCS 9710030233 | |
| Download: ML20211G766 (4) | |
Text
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- t UNITED STATES g
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NUCLEAR RESULATORY CflMMISSION t
WASHINGTON, D.C. 20066-0001 s*****/
1 September 30, 1997 NOTE TO:
File, South Texas Project l
l Janet Kennedy, Project Manager M %
FROM:
Project Directorate IV-1 Division of Reactor Projects III/IV
SUBJECT:
QUESTIONS SENT TO LICENSEE TO SUPPORT A REVIEW BY THE OFFICE FOR ANALYSIS AND EVALUATION OF OPERATIONAL DATA (AE0D)
The attached questions were faxed to the South Texas Project on September 29, 1997, to support an ongoing review by AEOD regarding two events at STP in 1989 involving the failure of both solid state protection system undervoltage output boards during surveillance testing.
Both events were entered in the Nuclear Plant Reliability Data System (NPRDS) by the licensee in 1991. AE00 is investigating the possibility of classifying these events as
" risk-significant" and needs the information identified on page 2 of the attachment from the licensee. At this time, the licensee has voluntarily agreed to provide the requested information.
Attachment:
As stated DISTRIBUTION:
TAlexion Central File PD4-1 r/f
-PDR i J: /;l 9710030233 970930 8M"
^
Sept':mber 26,1997 SOUTH TEXAS UNIT-1 POTENTIAL RPS FAILURE EVENT
References:
1.
-Two NPRDS event entries (see attachment 1) a.
Event 1:
South Texas Unit-1 Failure Discovery Date: 8/28/89 Component: INTCPM -
Utility Component ID: 3Z101ZRR001 - A520 b.
Event 2:
South Texas Unit Failure Discovery Date: 8/28/89 Component: INTCPM Utility Component ID: 3Z101ZRR008 - A520 2.
NRC Information Notices:
a.
IN 85-18, dated March 7,1985, " Failure of Undervoltage Output Circuit Boards in the Westinghouse-Designed Solid State Protection System' b.
. IN 85-18, Supplement 1, dated September 10,1991 3.
NRC Inspection Report 50-498/89-30, dated 9/26/89
Background
1.
Utility entered two events into NPRDS on 3/21/91 documenting the failure of both Solid State Protection System (Trains'R' and "S') undervoltage Wput boards during surveillance testing while in a refueling outage (Ref. '1).
2.
Two information notices were issued describing similar RPS failure events and the failure mechanism (Ref. 2).
3.
Unit 1 had an automatic reactor trip on 7/04/89. The unit entered into mode 3 during a controlled shutdowii (no automatic reactor trip) on 8/5/89 for a refueling outage (Ref. 3)
ATTACWtENT
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September 26,1997 Questions:
1.
Was a root cause analysis documented for the 8/28/89 undervoltage (UV) output board failures? P yes, please provide a copy of the report.
2.
What test was being performed on 8/28/89 that detected the failures?
3.
Did both failures occur at the time of the 8/28/89 surveillance test?
4.
If the 8/28/89 surveillance test did cause the failures, then:
a.
What test was being performed on 8/28/89 that caused the failures?
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b.
How was the determination made that a surveillance test caused the failures?
1 How was the determination made that each UV output board was NOT damaged c.
during a previous maintenance or surveillance activity sometime after the 4
7/04/89 automatic reactor trip and before 8/28/89 surveillance test that caused the failures?
d.
Was the trip capability of each board verified before the 8/28/89 surveillance test that caused each failure?
Note: A UV output board produces a 48 vde output voltage when the associated RPS train is NOT in the tripped condition. When a trip signal from the associated RPS train is generated, a non-damaged UV output board is suppose 2
to cut the output voltage to 0 vdc. However, the output voltage from a damaged j
UV output board in the not-failed-safe condition stays at 48 vde when the RPS l
train is tripped.
5.
Concoming surveillance testing of the UV output boards:
l a.
Approximately how often is a UV output board involved in a surveillance test?
i b.
Do procedures at STP require testing of the UV output boards after reactor trip l
breaker maintenance and surveillance tests?
6.
When was each undervoltage output circuit board tested during the time period between the 7/04/89 automatic reactor trip and the 8/28/89 surveillance test? Please provide for each surveillance test the date and type of test.
7.
~
When were maintenance and surveillance activities conducted on each reactor trip breaker during the time period between 7/04/89 and 8/28/897 Please provide for each activity the date and a brief one-line description of the maintenance activity or type of test.
~.. _
3 Septsmber 26,1997 ATTACHMENT NPRDS Event Descriptions Event 1:
DD: 08/28/89 Desc: WHILE PERFORMING TIME RESPONSE TESTING, MAINTENANCE PERSONNEL FOUND THAT THE SOLID STATE PROTECTION SYSTEM TRAIN 'R' UNDERVOLTAGE OUTPUT BOARD OUTPUT FAILED TO DROP FROM 48 VDC TO O VDC ON A REACTOR TRIP SIGNAL SIMULATION. THE CHANNEL WAS LOST.
THE PLANT WAS IN AN OUTAGE SO THERE WAS NO AFFECT ON THE PLANT.
Cause: THE UNDERVOLTAGE OUTPUT BOARD CIRCU!TRY WAS DEFECTIVE AND NOT ISOLATED TO ANY ONE SUBCOMPONENT,
Action: UNDERVOLTAGE OUTPUT BOARD WAS REPLACED AND RETUPNED TO SERVICE,
Mfr. W120 - Westinghouse Elec Corp / Hagan
Mod Num: 6058D45G01 Mod Id: 6058D45 Event-2:
DD: 08/28/89 Desc: WHILE PERFORMING TIME RESPONSE TESTING, MAINTENANCE PERSONNEL FOUND THAT THE SOLID STATE PROTECTION SYSTEM TRAIN 'S' UNDERVOLTAGE OUTPUT BOARD OUTPUT FAILED TO DROP FROM 48 VDC ON A REACTOR TRIP SIGNAL SIMULATION. THE CHANNEL WAS LOST, THE PLANT WAS IN AN OUTAGE SO THERE WAS NO AFFECT.
Cause: TPE UNDERVOLTAGE OUTPUT BOARD CIRCUITRY WAS DEFECTIVE AND NOT ISOLATED TO ANY ONE SUBCOMPONENT.
Action: UNDERVOLTAGE OUTPUT BOARD WAS REPLACED AND RETURNED TO SERVICE.
Mfr: W120 - Westinghouse Elec Corp / Hagan
Mod Num: 6058D45G01 Mod Id: 6058D45 J