ML18096A230
| ML18096A230 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 08/22/1991 |
| From: | Vondra C Public Service Enterprise Group |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 91-02, 91-2, NUDOCS 9109030022 | |
| Download: ML18096A230 (5) | |
Text
~I OPS~G Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge, New Jersey 08038 Salem Generating Station U. S. ~uclear Regulatory Commission Document Control Desk Washington, DC 20555
Dear Sir:
SALEM GENERATING STATION LICENSE NO. DPR-70 DOCKET NO. 50-272 UNIT NO. 1 SPECIAL REPORT 91-2 August 22, 1991 This Special Report addresses a Reactor Trip Breaker failure.
It has been prepared in accordance with the reporting requirements of Technical Specification 3.3.1.1 Table 3.3-1 pursuant to Technical Specification 6.9.1.9. It is being submitted within thirty (30) days as required.
MJP:pc Distribution Sincerely yours, 1/c#~/~
- c. A. vo.d:a.Cf...,-
General Manager -
Salem Operations 9109030022 90~ggij~72 PDR ADOCK PDR s
The Energy People 95-2189 (10Ml 12-89
SPECIAL REPORT NUMBER ~2 PLANT IDENTIFICATION:
Salem Generating Station - Unit 1 Public Service Electric & Gas Company Hancock's Bridge~ New Jersey 08038
- IDENTIFICATION OF OCCURRENCE:
Reactor Trip Breaker Failure Event Date(s}:
7/25/91 Report Date:
8/22/91 This report was initiated by Incident Report No.91-508.
CONDITIONS PRIOR TO OCCURRENCE:
Mode 1 Reactor Power 100% - Unit Load 1120 MWe DESCRIPTION OF OCCURRENCE:
This report documents a Reactor Trip Breaker failure as required by Technical Specification 3.3.1.1 Table 3.3-1 Notation ### which states:
"If ACTION Statement 1 is entered as a result of Reactor Trip Breaker (RTB} or Reactor Trip Bypass Breakers (RTBB) maintenance testing results exceeding the following acceptance criteria, NRC reporting shall be made in accordance with Specification 6.9.1.9:
- 1.
A RTB or RTBB trip failure during any surveillance test with less than or equal to 300 grams of weight added to the breaker trip bar.
- 2.
A RTB or RTBB time response failure that results in the overall reactor trip system time response exceeding the Technical Specification limit.
During normal power plant operation, on July 25, 1991, at 0941 hours0.0109 days <br />0.261 hours <br />0.00156 weeks <br />3.580505e-4 months <br />, Technical Specification 3.3.1.1 Action 1 was entered in support of surveillance testing of the "A" RTB.
At 1010 hours0.0117 days <br />0.281 hours <br />0.00167 weeks <br />3.84305e-4 months <br /> that day, the RTB failed to meet the time response (to open) test requirement of 10 cycles when it opened 16 cycles after actuation of the trip signal (i.e., after the 43 VDC test signal was removed from the undervoltage trip attachment coil).
The P-250 printout results of this first test was delayed (by approximately 1 minute) putting in question the validity of the printout.
Therefore, a second test was performed.
The breaker did not open during this second test even though the trip signal was active for approximately three (3) seconds.
A computer technician had been conducting P-250 testing concurrent with the first breaker test.
This delayed the first breaker test result's printout.
Technical Specification 3.3.1.1 Action 1 states:
"With the number of channels OPERABLE one less than required.by the Minimum Channels OPERABLE requirement, be in HOT STANDBY within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />; however, one channel may be bypassed for up to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> for surveillance testing per Specification 4.3.1.1 provided the other channel is OPERABLE."
I tnlIT 1 SPECIAL REPORT ~2 APPARENT CAUSE OF OCCURRENCE:
The cause of the reactor trip breaker failure is equipment failure.
The failed breaker is a Westinghouse DB-50.
The breaker's undervoltage trip attachment (UVTA)
(-see attached drawing for UVTA detail) had failed.
Testing of required trip bar force was successfully completed.
Testing of the UVTA lever force was unsuccessful.
The UVTA trip lever force was insufficient to trip the "trip bar", which de-energizes the breaker, with no test weight added to the trip bar.
The UVTA was sent to Westinghouse for detailed testing in support of root cause failure analysis.
This testing identified increased friction between the latch and latch spring.
Further investigation showed that the latch spring had a groove "cut" into the spring where the latch rides up and down.
The latch did not appear to have the required finished surface~ The latch was serrated at one point on the latch.
The preliminary findings by Westinghouse and PSE&G Quality Assurance personnel indicate that these defects are the cause of the erratic performance of this UVTA's lever force trip capability.
The specific cause of the latch surface defect(s) has not been determined; however, it should.be noted that the UVTA assembly is only handled by the vendor.
Therefore, the root cause of this event is "design, manufacturing, construction installation" as per NUREG 1022, "Licensee Event Report System".
ANALYSIS OF OCCURRENCE:
There are two (2) reactor trip breakers ("A" and "B").
They are in series which connect the output of the rod drive motor generator sets to the rod control power cabinets.
In the event of a reactor trip signal, these.breakers open, removing power from the control rod drive mechanisms allowing the control rods to drop into the reactor core.
The opening of either breaker will cause this to occur.
Two (2) RTBBs are provided to allow surveillance testing at power.
To ensure proper functioning of the breakers, functional surveillances are performed as prescribed in the Technical Specifications.
These functional tests include a measurement of the force required to move the breaker trip bar.
In this event, the trip bar failed to move when initially called upon thereby preventing the opening of the "A" reactor trip breaker within 10 cycles.
The "B" reactor trip breaker did successfully complete its last surveillance and was therefore functional.
Power to the control rod drive mechanisms would have been terminated with the opening of the "B" reactor trip breaker in the event of a reactor trip signal.
Therefore, this event did not affect the health or safety of the public; however, it is reportable to the commission as per the Technical Specifications.
As required by Technical Specification 3.3.1.1 Action 1, a load decrease was initiated at 1110 hours0.0128 days <br />0.308 hours <br />0.00184 weeks <br />4.22355e-4 months <br /> (on July 25, 1991) at a rate.of 10%/hr.
The Nuclear Regulatory Commission was notified (at 1110 hours0.0128 days <br />0.308 hours <br />0.00184 weeks <br />4.22355e-4 months <br />) of the Technical Specification required shutdown initiation as per Code of Federal Regulations 10CFR 50.72(b) (1) (i) (A).
The Action Statement and the load decrease were terminated at 1230 hours0.0142 days <br />0.342 hours <br />0.00203 weeks <br />4.68015e-4 months <br /> when the
UN'IT 1 SPECIAL REPORT 4t2
- ANALYSIS OF OCCURRENCE:
(cont'd) replacement breaker in the "A" RTB position successfully completed functional testing.
The Unit was then returned to full power operation.
CORRECTIVE ACTION:
The failed "A" RTB was replaced with the "B" RTBB.
On July 25, 1991, at 1230 hours0.0142 days <br />0.342 hours <br />0.00203 weeks <br />4.68015e-4 months <br />, upon successful completion of functional testing of the replacement breaker, Technical Specification 3.3.1.1 Action 1 was exited.
A detailed investigation report, of the Westinghouse UVTA testing, is being prepared.
The failed UVTA was the first UVTA used in a "lot" of eight (8) breakers.
The other UVTAs in the "lot" will be visually inspected.
One (1) of these UVTAs will be disassembled for detailed testing/inspection.
Additional actions will be taken based upon the testing/inspection results.
MJP:pc SORC Mtg.91-087
!NCt.OSUll! 6 ATTACHMENT - CONSTRUCTION
.U!RICATION DETAILS LATCH LOOP r-'1-- P TZ Al.I. !IUAFACES LATCH GUIDE PIN PT Z ALL SUAFACU ENLARGED VIEW 'f(
LATCH PIN PT 3 LATCH
\\
I ENLARGED VIEW B
~-- SEE ~
VI!Jf *s*
9VERITY SEALANT INTM:T AT POINTS A,l,C
~--SEE~VIEW 'A' Enclo1ure 6 ft.
?a..ae... I/ ~I t:3