ML20204J171
| ML20204J171 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 03/22/1999 |
| From: | Jonathan Brown UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-99-2013, NUDOCS 9903300017 | |
| Download: ML20204J171 (4) | |
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. A Global Energy Company March 22,1999 GDP 99-2013 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001 Portsmouth Gaseous Diffusion Plant (PORTS)
Docket No. 70-7002 l
Event Report 99-03 Pursuant to the 10CFR 76.120(d)(2), Enclosure i provides the required 30 day written Event Report, for an event involving a Criticality Accident Alamt System slave nitrogen operated hom unit failure at the Portsmouth Gaseous Diffusion Plant. Enclosure 2 is a list of commitments made in the report.
Should you require additional information regarding this event, please contact Scott Scholl at (740) 897-2373.
Sincerely, a Mt =
. Morris Brown General Manager
,/
Portsmouth Gaseous Diffusion Plant h
Enclosures:
As Stated ec:
NRC Region ill Office NRC Resident inspectors - PORTS
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9903300017 990322 PDR ADOCK 07007002
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PDR_
P.O. Box 800, Portsmouth, OH 45661 Telephone 614 897-2255 Fax 614-897-2644 http://www.usec.com Offices in Livermore, CA Paducah, KY Portsmouth, OH Washington, DC L.
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.o GDP 99-2013 Page 1 of 2 Event Report 99-03 Description of Event On February 19,1999, at approximately 2300 hours0.0266 days <br />0.639 hours <br />0.0038 weeks <br />8.7515e-4 months <br />, while investigating a Criticality Accident Alarm System (CAAS) trouble alarm, Instrument Maintenance personnel discovered the nitrogen cylinder valved off to the CAAS slave nitrogen' operated horn at column D-8 in the X-700 building. With l
the nitrogen supply to the CAAS slave hom valved off, the hom would be unable to alert personnel to evacuate in the event of a criticalit'. The failure to maintain an audible criticality accident alarm
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y in' this area of X-700 is reportable in accordance with 10CFR76.120(c)(2). - A discussion of the circumstances leading to the discovery of the closed valve is provided below.
On February 19,1999, at approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, the Cascade Controller received a trouble alarm from the CAAS slave unit. At approximately 1430 hours0.0166 days <br />0.397 hours <br />0.00236 weeks <br />5.44115e-4 months <br />, a Maintenance Front Line Manager (FLM) investigating the trouble alann reported to the Cascade Controller that the nitrogen cylinder pressure of the slave unit was approximately 1000 psig. This pressure was greater than the 900 psig minimum i
required by Technical Safety Requirement 2.8.3.1, but below the 1050 psig trouble alarm set point.
At approximately 2300 hours0.0266 days <br />0.639 hours <br />0.0038 weeks <br />8.7515e-4 months <br /> the same day, Instrument Maintenance personnel were preparing to replace the cylinder when they discovered the closed cylinder valve. When an attempt was made to close the valve to permit cylinder replacement, the valve would not turn, indicating that it was already in the fully closed position. Instrument Maintenance personnel then opened the valve. The manifold immediately increased in pressure to approximately 1800 psig and the trouble alarm cleared.
'Cause of Event '
The exact cause for this event could not be determined. The investigation of this event concluded
- that the event was most likely due to one of two possible causes; 1) the nitrogen cylinder valve was improperly left closed following previous maintenance activities,2) the valve was closed as part of an unauthorized activity. A discussion of these possible causes is provided below.
The investigation determined that maintenance activities associated with this CAAS slave horn occurred on February 16,1999. At that time the nitrogen supply valve was closed to allow work to be performed and later re-opened to pressurize the system for leak testing. This wc-k was completed at approximately 2230 hours0.0258 days <br />0.619 hours <br />0.00369 weeks <br />8.48515e-4 months <br /> on February 16,1999.
"A review of records associated with this work indicated that procedural steps which require the nitrogen supply valve to be opened, and independently verified open, were signed off by personnel performing the work. The Maintenance FLM supervising the work stated that he witnessed one
p GDP 99-2013 Page 2 of 2 Event Report 99-03 individual check the valve as open, and a different individual perform a hands on independent verification that the valve was opened. The Maintenance FLM and the two individuals performing the verifications were experienced individuals who have performed this work successfully numerous times in the past. Based on this information, the investigation concluded that it is unlikely that the valve was left closed following the previous maintenance activity.
The investigation also considered the possibility that the valve was closed as a result of an unauthorized activity. However, no activities that could have resulted in inadvertent closure of the valve could be identified. Administrative controls, such as tamper indicating devices (TIDs), were not used for this valve. As a result, the investigation could not determine if an unauthorized activity caused this event.
Corrective Actions 1.
On March 1,1999, plant personnel performed verification that nitrogen cylinders on CAAS systems, including slave nitrogen-operated horn units, were valved open. Nitrogen cylinders were sealed in the open position using lead wire seals where possible. In cases where the valve design ( i.e. solid valve handles) precluded installing lead wire seals, indicating tape was applied as a TID.
2.
By March 24,1999, TIDs will be applied to nitrogen cylinders that were identified as having solid valve handles and were not sealed previously.
3.
By April 15,1999, CAAS maintenance procedures will be revised to require that nitrogen cylinders be sealed in the open position using TIDs.
Extent of Exposure ofIndividuals to Radiation or Radioactive Materials i
There were no exposures to individuals from this incident to radiation or radioactive materials.
Lessons Learned The investigation was unable to determine dermitively whether the valve was left closed during maintenance or whether closure occurred later. The installation of TIDs will make it less likely that l
a CAAS nitrogen cylinder valve could be inadvertently closed.
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Event Report 99-03
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List of Commitments 1.
By March 24,1999, TIDs will be applied to nitrogen cylinders that were identified as having j
solid valve handles and were not sealed previously.
2.
By April 15,1999, CAAS maintenance procedures will be revised to require that nitrogen
- cylinders be sealed in the open position using TIDs.
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