ML20236H603
| ML20236H603 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 07/01/1998 |
| From: | Pulley H UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-1046, NUDOCS 9807070281 | |
| Download: ML20236H603 (4) | |
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d USEC A Global Energy Company July 1,1998 GDP 98-1046 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-98-16 Pursuant to 10 CFR 76.120(d)(2), enclosed is the required 30-day report related to the failure.of
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a C-310-A UF detector to reset during testing on June 2,1998. The Nuclear Regulatory 6
Commission (NRC) was notified of the event on June 3,1998, at 0053 hrs. (NRC No. 34329).
Any questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
Sincerely, h
Howard Pulley General Manager Paducah Gaseous Diffusion Plant
Enclosure:
As Stated cc: NRC Region III Office
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NRC Resident Inspector - PGDP 1
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l 9807070281 990701 PDR ADOCK 07007001 C
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P.O. Box 1410, Paducah, KY 42001 Telephone 502-441-5803 Fax 502-441-5801 http://www.usec.com 05ces in Livermore. CA Paducah. KY Portsmouth, OH Washington, DC
Docket No. 70-7001 GDP 98-1046 Page 1 of 3 EVENT REPORT l
ER-98-16 DESCRIPTION OF EVENT
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On June 2,1998, at 0830 hrs., during the twice per shift surveillance testing of the C-310 UF6 leak detection safety system required by TSR SR 2.3.4.4-1, detector head YE48-2 fired on demand, as required, but would not reset. This " test firing" of the detectors is accomplished by applying an external voltage to the detector causing the internal cold-cathode tube to conduct through and generate an alarm condition. This " test firing is required in high temperature applications to reset a firing history effect that causes detectors to become less sensitive over long exposures to elevated temperatures. After the tube " fires," it is reset by momentarily removing power. When the subject detector locked in the alarm condition, it could not have detected and alarmed on an actual UF release. Due to this loss of detectability function, the plant shift 6
superintendent (PSS) decir. red the UF detection system inoperable and ordered entry into the 6
general limiting conditions for operation (LCO) at 0903 hrs.
The Nuclear Regulatory Commission Headquarters (NRC-HQ) operations office was notified in accordance with 10CFR76.120(c)(2) on June 3,1998, at 0053 hrs., and NRC No. 34329 was assigned to the notification.
The failure occurred on the UF detection system that monitors the UF condenser, accumulator, 6
6 and piping heated housings in C-310-A. In particular, the detector that experienced the failure monitors the piping housing on the ground floor of C-310-A associated with the abandoned Twelliot product withdrawal pumps. These pumps have been out of service for years and are cut and capped. However, the housing still contains a section of high pressure UF piping between 6
the Normetex product withdrawal compressors and UF condensers. This area is additionally 6
monitored by another UF leak detector located in the housing and two detectors mounted or, the 6
ceiling above the piping housing. While these detectors cannot be said to provide exact monitoring capability of the failed detector, it is highly probable that a release in the housing would be detected by one or more of these detectors.
Docket No. 70-7001 I
GDP 98-1046 Page 2 of 3 CAUSE OF THE EVENT
' A. Direct Cause-The model of detector subject to this report compares the resistance of an open sample chamber to a semi-sealed reference chamber. If sufficient, airborne, particulate matter (UO F ) enters the sample chamber, the resistance of the chamber increases with respect to I
2 2 the reference chamber causing an alarm. It is believed that a slight build-up of foreign material (dust, dirt, contaminants) inside the detector sample chamber caused a higher-than-normal resistance path across the chamber. This, in combination with the fact that the test firing caused the detector to be at maximum sensitivity, simulated a release to the detector and caused a false alarm that could not be reset. This failure is mitigated by the other detectors in the area, and the fact that the operator conducting the surveillance was within approximately 30 feet and in line-of-sight with the detector and would have observed any actual release event.
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I B. Root Cause The root cause of this event is attributed to the lack of preventative maintenance (PM) which allowed an excessive amount of contaminants to build-up inside the detector sample chamber.
causing the detector to fail in'the alarm condition.
In industrial environments, such as those at PGDP, it is inevitable that some level of dust will always be present. However, build-up of this dust on plant components is very slow and varies with the environment immediately surrounding that component. As previously stated, the slight buildup of dirt increases the sensitivity resulting in more conservative alarming.
There are approximately 700 detectors of this model at PGDP currently maintained in environments similar to that found in the housing in C-310-A. Surveillance are conducted twice per shift on these detectors, in accordance with TSR requirements. The relative infrequency of this type of failure makes it unlikely to have multiple detectors in the same area fail simultaneously, i
Also, as in this particular event, most areas requiring leak detection are monitored by multiple detectors.. While these detectors are not technically redundant, they do provide a level of assurance that significant leaks would not go' unnoticed. Additionally, workers in the immediate area are protected by following the "See and Flee" Policy.
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Docket No. 70-7001 GDP 98-1046 Page 3 of 3 l:
l It is likely that periodic, preventative cleaning of detectors would result in longer periods of L
inoperability for these required systems than is caused by failures of this type at the current frequency. These factors lead to'the conclusion that no new PM task for detector cleaning is
. warranted at this time.
CORRECTIVE ACTIONS A. Corrective Actions Taken
- 1. ' n June 2,1998, the failed detector was replaced.
O EXTENT EXPOSURE OF INDIVIDUAT R TO RADIATION OR RADIOACTIVE MATERIAIR There was no release of radioactive materials related to this event and, thus,' no exposure to l
personnel.
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- IRRSONS IFARNED
- UF detectors that fail to reset after test firing cannot perform their detection function.
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