ML20206P055
| ML20206P055 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 05/10/1999 |
| From: | Pulley H UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-99-1013, NUDOCS 9905180131 | |
| Download: ML20206P055 (4) | |
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l May 10,1999 GDP 99-1013 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-99-05 Pursuant to 10CFR76.120(d)(2) enclosed is the required 30-day written event report for the failure of the UF, Release Detection. safety system in C-333, Unit 5, Cell 4. The Nuclear Regulatory Commission Headquarters (NRC-liq) eperations office was notified of the event on April 13,1999 (NRC No. 35589).
- Any questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
Sincerely, Qs-ioward Pulley General Manager Paducah Gaseous Diffusion Plant
Enclosures:
As Stated cc: NRC Region 111 Office NRC Resident inspector-PGDP fl 9905180131 990510 s
PDR ADOCK 07007001
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C PM 110.11ox 1410, Paducah, lW 42001 Telephone 502-441-5803 Fax 502-441-5801 http://www.usec.com Offices in Livermore, CA Paducah, LT Portsmouth, OH Washington, DC L
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Docket No. 70-7001 GDP 99-1013 Page1of3 EVENT REPORT ER-99-05 DESCRIPTION OF EVENT On April 11,1999, at 2350 hrs., the Paducah Gaseous Diffusion Plant (PGDP) Plant Shin Superintendent (PSS) was notified that the UF. release detection safety system in C-333, Unit 5, Cell 4 had failed dtuing the twice-per-shift (every 6-8 hours) surveillance testing required by Technical Safety Requirement (TSR) 2.4.4.1-1. The PSS declared the system inoperable and directed the implementation of TSR required actions, which included placing a " smoke watch" in the affected area (TSR 2.4.4.1-B1). The smoke watch was implemented at 0005 hrs. on April 12,1999. At the time of the failure, C-333, Unit 5, Cell 4 was operating above atmospheric pressure (TSR Mode 2). Actions were initiated to bring the operating pressure of the affected equipment to below atmospheric pressure (TSR Mode 1). At 0125 hrs.,
on April 12,1999, Unit 5, Cell 4 was brought to Mode I status. In Mode 1, the UF. detection safety system is not required to be operable.
At 0130 hrs., on April 12,1999, the PSS was informed that the testing failure had actt' ally occurred at approximately 2145 hrs., on April 11,1999. But the failure was not communicated to 15e building front-line manager. Thus, the required TSR actions were not implemented within one-hour, as required by the TSR.
At 1340 hrs., on April 13, 1999, the Nuclear Regulatory Commission Headquarters (NRC-HQ)
Operations office was notified of the event, as required by 10CFR76.120(c)(2). The failure to implement the actions required by TSR 2.4.4.1-B1 within the one-hour limit and to notify NRC within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of discovery of the safety system failure, have been entered into the plants corrective action process for investigation and development of corrective actions to prevent recurrence. The failure of the UF6 detection safety system during testing is an event reportable to NRC, per 10CFR76.120(c)(2) and is the subject of this report.
The UF. detection system is tested twice per shift or every 6 to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, as described in PGDP operations procedure CP4-CO-CN6020T, "TSR Surveillance Test Firing of PYR-A-LARM Type 1, High Voltage UF. Detection Systems in C-331; -333; -335; -337." This testing is only required by the TSR when the cascade equipment is operating above atmospheric pressure (Cascade Mode 2). In C-333 the detector heads are usually test fired every 6 to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> regardless of mode to maintain the sensitivity of the heads in the elevated temperatures, such as those found in the cell housing.
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Docket No. 70-7001 i
GDP 99-1013 Page 2 of 3 I
To perform this testing, building operators must go to the local cell panel. Upon arriving at the cell panel, the operator looks for a single red neon light labeled " ready" on the front panel of the UF6 detection power supply module which indicates that the UF detection signal conditioner is providing the 6
required 200-volt DC power to the detector heads. Then the manual test push-button switch, used to force all of the detector heads into an alarm state, is depressed and held for 1 to 10 seconds. This should cause the red neon detector indicator lights (one for each detector) to be illuminated for each detector that is in the alarm state. If all the detector heads lights are lit, the test is successful. The operator depresses the system reset push-button switch, retuming the system to operable status and proceeds to the next cell and repeats the test.
Prior to manually test firing the UF detectors at C-333, Unit 5, Cell 4 cell panel, the signal conditioners 6
" ready" light was verified to be lit. When the manual test push-button switch was depressed, the operator stated that the detector indicator lights " flickered" momentarily, but did not remain illuminated. When the manual test push-button switch is pressed it energizes a part of the circuit through wires that are not energized except during test firing or actuation of the detector heads. Thus, the failure coincided directly with the test.
The troubleshooting work package task history indicated that one of these wires (No. 2 wire to detector YE-16) was found spliced. The splice was made by twisting the bare wires together and was not insulated, instead of being crimped together with insulated butt splices. It is not known when this splice was made, but indications are that it could have been made during original installation years ago.
The flickering lights and subsequent failure to illuminate, noted by the operator, is indicative of a partial ground on the No. 2 wire from the detector. A partial ground means that there is intermittent contact of an energized circuit-to-ground or a high resistance path-to-ground. When the manual test push-button switch was depressed, a voltage was applied on the No. 2 wire propagating the partial ground to a full ground and the intermittent contact became direct contact. This ground or short circuit on the output of the power supply caused a failure of the UF detection signal conditioner power supply that removed the 6
200-volt DC from the detector heads.
Since prior testing of this system was successfully completed, it is assumed that the bare wire made full enough contact with the conduit to cause the direct short initiated by the test at some point in the 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> prior to the subject testing at 2145 hrs., on April 11,1999. Had a significant UF release occurred during 6
this time, it would have been detected by other operable detectors in the adjacent cells and bypass housings. Thus, alerting operators to take appropriate alarm response action to stop the release.
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Docket No. 70-7001 GDP 99-1013 Page 3 of 3 CAUSE OF EVENT A. Direct Cause The direct cause is attributed to the direct ground, which failed the signal conditioner power supply.
This removed the 200-volt DC from the detectors, rendering them inoperable.
B. Root Cause The root cause is attributed to the LTA maintenance work controls applied to work on safety systems in past years. The condition of the wire splice indicates that this was done many years ago and thus, is seen as a legacy work quality and control issue that could not occur under current work control and conduct of maintenance quality requirements. The PGLD system is classified as a "Q" safety system.
The wire is a "Q" component of this system and as such any maintenance is strictly controlled by the plant's work control process requirements. A search of the maintenance work history and problem reporting databases did not indicate that this type of condition is a generic problem that could impact other systems.
CORRECTIVE ACTIONS A. Completed Corrective Actions
- 1. The poor quality wire splices were replaced and the system tested prior to returning it to service.
B. Planned Corrective Actions Given the legacy nature of the poor workmanship discovered and the lack of an identified trend of this type of failure, further corrective actions are not necessary. The current work controls will ensure that this type of workmanship does not occur in the future.
EXTENT OF EXPOSURE OF INDIVIDUALS TO RADIATION OR RADIOACTIVE MATERI ALS -
None LESSONS LEARNED N/A