ML20203J701
| ML20203J701 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 02/27/1998 |
| From: | Morgan J UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-2010, NUDOCS 9803040245 | |
| Download: ML20203J701 (5) | |
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OSEC A Glot,al Energy Company Febniary 27,1998 ODP-98-2010
-t United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 Portsmouth Gascous Diffusion Plant (PORTS)
Docket No. 70-7002 Event Report 97-01, Revision 2 Pursuant to the Safety Analysis Report (SAR), Section 6.9, Table 6.91, J (2), Enclosure 1 provides Event Report 97-01, Revision 2. The revised event report provides notification of a change to a corrective action comploion date regarding the installation of an upgraded Tails Withdrawal variable bufTer system. Changes from the previous report are marked with a vertical line in the right margin, is a list of commitments made in the report, including the revised corrective action date.
Should you require additional information regarding this event, please contact Scott Scholl at (614) 897-2373.
Sincerely, N
J e
Acting Gener ianager Portsmouth Gaseous Diffusion Plant
Enclosures:
As Stated gg. 7 ~..)
cc:
NRC Region 111 Office NRC Resident inspector - PORTS 9803040245 900227' PDR ADOCK 07007002 f
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110. Box 800, Portsmouth, OH 45661 Telephone 614-897-2255 Fax 614 897-2644 http://www.usec.com OtTices in Livermore, CA Paducah, KY Ponsmouth, OH Washington, DC
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GDP 98-2010 Page1of3 Event Report 97-01 Description of Evat -
' On March 20,1997, at 1409 hours0.0163 days <br />0.391 hours <br />0.00233 weeks <br />5.361245e-4 months <br /> while performing withdrawal operations at the Tails Side Withdrawal Station, the Car.cade Automatic Data Processing (CADP) smoke detector, designated as SSWL, alarmed in Area Control Room (ACR) #2 in the X-330 Process Building. Operations personnel investigated the alarm and observed smoke emanating from the area of compressor 30 WB-1, which had been operating in the withdrawal mmie 3. Operations personnel in the area followed the "See & Flee" policy and evacuated the affected area. Building recall was sounded to have all personnel report to their respective areas.
According to the Technical Safety Requirements for the Portsmouth Gaseous Diffusion Plant, the CADP smoke detectors are required to be operable when the Tails Withdrawal Station is operating in Modes II, Ill, or IV. In this instance, the Tails Side Withdrawal was operating in Mode III, which -
would make the actuation of this smoke detector alann reportable in accordance with the Safety Analysis Report, Section 6.9, Table 6.9 1, J (2).
Prior to initiating the withdrawal, the compressor was out of service for repair of a leak at the compressor flange. _ At 1755 hours0.0203 days <br />0.488 hours <br />0.0029 weeks <br />6.677775e-4 months <br /> on_ March 19,1997, compressor 30 WB-1 was started. At 2330 hours0.027 days <br />0.647 hours <br />0.00385 weeks <br />8.86565e-4 months <br />, compressor 30 WB-1 was charged with UF and valved into service. On March 20,1997 at 1315 hours0.0152 days <br />0.365 hours <br />0.00217 weeks <br />5.003575e-4 months <br />, the Tails Side Withdrawal was started. Within 54 minutes, at 1409 hours0.0163 days <br />0.391 hours <br />0.00233 weeks <br />5.361245e-4 months <br />, CADP smoke -
-detector SSWL, located above compressor 30 WB-1, actuated. At 1412 hours0.0163 days <br />0.392 hours <br />0.00233 weeks <br />5.37266e-4 months <br />, the Pyrotronics smokehead XAH300B1, which provides a redundant smoke detection system in Tails, also fired.
' At 1417 hot.rs, the compressor was shut down from the ACR and the alarm on SSWL cleared. At 1419 hours0.0164 days <br />0.394 hours <br />0.00235 weeks <br />5.399295e-4 months <br />, an Operator wearing proper personnel protective equipment responded to the area and found smoke emanating from the area of compressor 30 WB-1.
Add;tional emergency personnel were called and responded to the area. Emergency responders monitoring the area did not detect airborne contaminants. - Health Physics reported all air samples and radiological surveys as less than detectable and no evidence of an UF. release. An "All riear"
- was given on the building recall at 1506 hours0.0174 days <br />0.418 hours <br />0.00249 weeks <br />5.73033e-4 months <br />.
Following the All Clear, Operations and Maintenance personnel investigated the affected equipment
.and found no evidence of a failed compressor seal, which was considered the most likely source of a UF. leak in this area. Since there was no evidence indicating that the smoke originated from a UF.
release, plant personnel initiated an investigation to determine the source of the smoke.
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Enciasure 1 GDP-98-2010 Page 2 of 3 Event Report 97-01 On March 23,1997, maintenance removed a housing panel and found residue indicating that UF.
outgassing had occurred. Visible contamination was found on and around the WWB-27 compressor discharge block valve. A leak check performed on the valve bellows at 1715 hours0.0198 days <br />0.476 hours <br />0.00284 weeks <br />6.525575e-4 months <br /> determined there was a leak. On March 24,1997, following confirmation of an UF. outgassing as the cause of the CADP alarm, it was determined the occurrence was reportable to NRC.
The valve with the failed bellows w*1ich caused the outgassing was a 4-inch, model G 17 gate valve, manufactured by the Crane Company.
The material that outgassed was enriched UF. at approximately 3.0% U-235.
Cause of Event The direct cause of the UF. release was failure of the bellows on the WWB-27 compressor discharge block valve. The leaking bellows allowed the process gas to escape which set off the smoke detectors above the nearby compressor. The CADP UF Smoke Detection System SSWL smokehead and Pyrotronics smokehead XAH300B1 actuated in the Tails Withdrawal Area.
The root cause of the outgassing was the design of the valve butter system. The purpose of the valve buffer is to prevent the buildup of UF. in the valve stem cavities by keeping the buffer pressure l
approximately 5 psi above the maximum process gas pressure. The valve buffer system was designed to automatically switch from a low pressure (10 psig) to a high pressure (25 psig) buffer supply as the process gas pressure increases. The high pressure supply flows through an orifice which limits the buffer air flow rate. The bellows leak caused the buffer pressure to drop low enough, allowing the process gas to escape. To improve the ability of tin buffer system to prevent a UF. release, an enhancement to the system design has been identified. A new design will provide a variable pressure buffer system which will maintain the buffer air supply at a constant differential above the process pressure.
The existing valve buffer symra has operated without incident in excess of 8 months, due in part to the routine integrity checks by Operation's personnel, in addition,25% of the G-17 valve bellows have recently been replaced; thus enhancing system reliability and reducing the probability of outgassing through a failed valve bellows.
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The design of the enhanced variable buffer system is complete and final approval for installation was I
received February 10,1998. The Tails Withdrawal Station was removed from senice on February l
22,1998, for final installation of the buffer instrumentation. The Tails Withdrawal Station will not I
reestablish UF flow until completion ofinstallation and testing. If required, the Tails Withdrawal I
may remain out of senice following installation for further maintenance and testing.
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GDP-98-2010 Page 3 of 3 Event Report 97-01 Corrective Actions By March 31,1998, a new, upgraded variable buffer system at the Tails Withdrawal Station will be installed to maintain a buffer pressure above the process pressure.
l Extent of Exposure ofIndividuals to Radiation or Radioactive Materials There were no significant exposures to individuals from this incident to radiation or radioactive materials. The operator who investigated the smoke alarm submitted a sample for urinalysis. The bioassay results were below 5 ug/hter for soluble uranium (flag level). The calculated intake was 1.25 micrograms of uranium. The limit for occupational workers is 10,000 micrograms of soluble uranium per week.
Lessons Learned Personnel responded appropriately to this event in accordance with the "See and Flee" policy.
A correctly operating buffer air system is necessary to mitigate the elTects of small bellows leaks and prevent releases from occurring.
- 4 GDP-98-2010 Page1of1-Event Report 97-01 List of Commitments By March 31,1995, a new, upgraded variable buffer system at the Tails Withdrawal Station will be I
installed to maintain a buffer pressure above the process pressure.
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