ML20236U723
| ML20236U723 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 07/24/1998 |
| From: | Pulley H UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-1058, NUDOCS 9807300398 | |
| Download: ML20236U723 (5) | |
Text
,
9 d USEC
. A ciobal Energy company i
July 24,1998 GDP 98-1058 l
United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001 Paducah Gaseous Diffusion Plant (PGDP)
Docket No. 70-7001 Event Report ER-98-20 Pursuant to 10CFR76.120(d)(2), enclosed is the required 30-day written event report relateu.a the disabling of the CAAS audibility function in C-333, C-333-A, C-337, C-360 and C-720, due to a breaker trip on June 27,1998.
Any questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
l Sincerely, i
lloward Pulley General Manager j
Paducah Gaseous Diffusion Plant
Enclosure:
As Stated cc:
NRC Region III Office
'),
NRC Resident Inspector-PGDP
/
9807300398 990724 PDR ADOCK 07007001 C
PDR P.O.11ox 1410 Paducah, KY 42001 Telephone 502-441-5803 Fax 502-441-5801 http://www.usec.com Offices in Livermore, CA Paducah, KY Portsmouth, OH Washington, DC
Docket No. 70-7001 GDP 98-1058 Page 1 of 4 EVENT REPORT ER-98-20 DESCRIPTION OF EVENT On June 27,1998, at 1739 hrs., a 48-volt DC (VDC) circuit breaker in the central control facility (C-300) radiation alann annunciator cabinet B tripped unexpectedly. The circuit breaker (RA-5) provides 48-VDC control power to the Criticality Accident Alann System (CAAS) clusters in C-333,
' C-333-A, C-337, C-360, C-710, C-720 and C-746-Q facilities. As a result of this 48-VDC power failure, the CAAS audibility function (building horns) and the building warning beacons were partially disabled in all of the above facilities, with the exception of C-746-Q, which has no building hom and C-720, which has an alternate method to actuate building horns independently of the 48-VDC circuit.. The loss of 48-VDC associated with the RA-5 breaker trip did not adversely affect the cluster's ability to detect a criticality,1,ut would have prevented the clusters from initiating an alarm in C-300 used under the Justification for Continued Operation (JCO) for Compliance Plan 50. The loss of 48-VDC provided through the RA-5 circuit would not preclude CAAS local horns, which are separate from building horns, from functioning.
The breaker trip was annunciated as a "DC power failure" and AJ CAAS cluster " trouble" alarm on the C-300 CAAS alarm panel. At the time the trip occurred, the CAAS System Engineer was in C-300 and immediately went to annunciator panel B located in the.C-300 basement and, at 1741 hrs.,
asked an Electrician to close/ reset the RA-5 breaker. This restored normal power to the affected CAAS equipment. No subsequent breaker trips occurred.
.l The disabling of the CAAS horns in the subject facilities for this two-to three-minute period, when they are required by TSR to be available and operable, is reportable pursuant to 10CFR76.120(c)(2).
The Nuclear Regulatory Commission Headquarters (NRC-HQ) Operations office was notified of the event on June 28,1998, at 0101 hrs., and NRC Notification No. 34446 was assigned. Additionally, i
the failure to annunciate a CAAS alarm in C-300 would preclude notification of personnel in facilities adjacent to the affected buildings, as required, by the JCO under Issue 50 of the Compliance Plan.
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Prior to the subject breaker trip, construction activities had been underway for some time to complete the installation of new CAAS clusters in the C-710 laboratory facility. The project was installed by f
a sub-contractor with final electrical ties being made by PGDP Maint-nance personnel. All work was controlled by approved Maintenance Work Packages (MWP) and procedures. This included the installation of wiring and completion of final tie-ins for the C-300 control panels. This involved l
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i Docket No. 70-7001 GDP 98-1058 Page 2 of 4 terminating wiring, pulled in by the sub-contractor, in the new master terminal cabinet in the C-300 basement; also, terminating and pulling wiring from the master terminal control cabinet to the existing annunciator sub-panel B; then pulling wiring from the annunciator sub-panel B into the annunc' iator panel B and wiring in and installing relays. All non-safety material within C-300 was supplied by the sub-contractor. This work was completed on June 27,1998. The major work on this project involved electrical construction in the C-710 lab facility. At the time the RA-5 breaker tripped, there was no maintenance being performed on the system. The CAAS cluster logic cards had been installed and functioning properly since mid-morning on June 27,1998.
During troubleshooting to determine why the RA-5 breaker tripped, the logic card on cluster "AN" in C-710 was found to be damaged. The entire cluster was replaced on the morning of June 28, 1998. Later that day the logic card failed again. Engineering personnel investigated this problem and discovered that a relay, UV-48A located in C-710, showed signs of discolorations on the bottom of the relay (UV-48A) at Terminal 6 which is evidence of contact failure. The relay was said to be hot to the touch when first removed. The relay coil and remaining contacts were checked and found to be good. The current through the K2 contact (trouble contact) from cluster "AM" was measured after the second logic card failed. This was done because the under-voltage contacts for cluster "AM" are also located in UV-48A and to ascertain normal current load through a properly functioning K2 contact. The measurement showed load current at approximately 28 mA. Cluster "AN" was checked again with no problems noted.
The UV-48A relay and socket base (the base had signs of excess heat along one of the pin sockets) were removed and replaced. Cluster "AN" was then returned to service and no further problems have occurred.
The failed relay is a Potter & Brumfield #KUP-14D15-48. The relay is designated as UV-48A in the Radiation Alann Cabinet in the C-710 building. Its safety function is to detect a loss of 48-VDC to the C-710 CAAS system. Its contacts are installed in series in the trouble circuit of both cluster "AM" and "AN" in the radiation alarm cabinet.
The safety function of the C-710 trouble circuit is to alarm upon loss of 48-VDC power to the control logic and/or upon detection of a problem in the CAAS clusters.
As a part of the investigation, the current load on tripped breaker RA-5, which has a 10-amp rating, was evaluated. The total device load on the RA-5 breaker was determined to be approximately 5.2 amps. Therefore, RA-5 is sized adequately to handle the total load and did not trip due to any l
routine overload condition.
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l Docket No. 70-7001 j
GDP 98-1058 Page 3 of 4 Though the exact cause of the relay failure is unknown, it is apparent that the UV-48A relay contacts j
on the "AN" trouble circuit overheated, especially on Terminal 6. The heat was conducted down to the relay base, as well, on the same terminal. The contact material between Temlinals 9 and 6 is
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deformed in a manner not consistent with the other two contacts. In fact, there appears to be material between Terminals 6 and 9. Discoloration on all three terminals within the contact area can be seen.
Also, the stud fbr the contact at Terminal 6 is offset slightly toward the contact on Tenninal 9.
I The UV-48A relay contacts operate in a closed state and open on removal of voltage to the coil. It is believed that the contacts for the "AN cluster trouble circuit failed to close adequately, creating i
a situation where the contact was in a continuous switching mode. This switching on a DC circuit I
can cause high transients (voltages / currents) and resulted in eventual contact failure and an electrical fault on the circuit. Once the fault was established breaker RA-5 tripped, as designed. The damage to the logic card for the CAAS cluster, which is in series with the relay contacts, support this theory.
The design and the relay are the same that have been used in other CAAS systems and have been reliable as indicated by past operating experience. The relay was procured as a commercial grade item and dedicated for use upon receipt. The inspection plan and testing results were examined and found to be adequate.
CAUSES OF EVENT A. Direct Cause The disabling of the subject facilities CAAS building horns was caused by the RA-5 breaker action and resulting loss of 48-VDC power.
B. Root Cause The root cause is attributed to the unexpected failure of the UV-48A relay which created transients arcing, which led to over current conditions that damaged the two cluster logic cards and, when added to the existing load on RA-5, tripped the breaker.
CORRECTIVE ACTIONS i
l A. Completed Corrective Actions
- 1. On June 28,1998, the UV-48A relay was replaced.
i Docket No. 70-7001 GDP 98-1058 Page 4 of 4 B. Planned Corrective Actions l
Due to the nature of the failure and the lack of repetitive failures over a long operating period, l
no further corrective actions are planned at this time.
l EXTENT EXPOSURE OF INDIVIDUALS TO RADIATION OR RADIOACTIVE MATERIALS None LESSONS LEARNED N/A i
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