ML20206N832
| ML20206N832 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 12/18/1998 |
| From: | Jonathan Brown UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-2051, NUDOCS 9812220193 | |
| Download: ML20206N832 (6) | |
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. A ciob : sn.rry company December 18,1998 GDP 98-2051 United States Nuclear Regulatory Commission
' Attention: Document Control Desk Washington, D.C. 20555-0001 l
Portsmouth Gaseous Diffusion Plant (PORTS)
Docket No. 70-7002 Event Report 98-06, Revision 1 Pursuant to Safety Analysis Report (SAR), Section 6.9, Table 6.9-1, J (2), Enclosure i provides the revised 30-day written Event Report for an event involving an actuation of the Cascade Automatic Data Processing (CADP) Smoke Detection System in the X-330 Building at the Portsmouth Gaseous DifTusion Plant. The revised event report is being submitted to provide a root cause and corrective actions. Changes from the previous report are marked with a vertically dashed line in the right I
margin.
Should you require additional information regarding this event, please contact Scott Scholl at (614) 897-2373.
I Sincerely, h
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. Morris Brown l
General Manager
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Portsmouth Gaseous Diffusion Plant i
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Enclosures:
As Stated r
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NRC Region Ill Office NRC Resident inspector - PORTS J
9812220193 981218 U PDR ACOCK 07007002f C
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P.O. Ilox 800, Portsrnouth. Oil 45661 Telephone 614-897-2255 Fax 614-897-2644 http://www.usec.com i
J Offices in I.ivermore, CA Paducah, KY Portsmouth. Oli Wahington, DC
l GDP 98-2051 Page1of4 Event Report 98-06 Revision 1 l
Description of Event On April 24,1998, at 1807 hours0.0209 days <br />0.502 hours <br />0.00299 weeks <br />6.875635e-4 months <br />, while in withdrawal mode III, the Cascade Automatic Data Processing (CADP) smoke detectors SSWA and SSWE that monitor the Tails withdrawal area, alamled in the X-330 Process Building Area Control Room #2. The control room operator silenced the alarm and informed the First Line Manager (FLM). After observing the outleakage message and the location code of the smoke detector heads printed on the alarm typer, an operator was dispatched to investigate the smoke detectors' coverage area. The operator did not detect a UF outleakage or 6
other conditions that could have actuated the detectors. Since no smoke was detected, the alarm actuations were handled as spurious actuations in accordance with procedure XP4-CO-CA2245,
" Smoke Detection Portion of the CADP System." Smoke alarm SSWA cleared at 1810 hours0.0209 days <br />0.503 hours <br />0.00299 weeks <br />6.88705e-4 months <br /> and SSWE cleared at 1813 hours0.021 days <br />0.504 hours <br />0.003 weeks <br />6.898465e-4 months <br />. On Apal 26,1998, at 1222 hours0.0141 days <br />0.339 hours <br />0.00202 weeks <br />4.64971e-4 months <br />, while in withdrawal mode Ill, CADP smoke detector SSWE alarmed for the second time. Operations personnel again responded in accordance with procedure XP4-CO-CA2245. The operator did not detect UF outleakage. This alarm actuation was also handled as a spurious actuation. The alarm cleared at 1225 hours0.0142 days <br />0.34 hours <br />0.00203 weeks <br />4.661125e-4 months <br />.
On April 27,1998, at 0930 hours0.0108 days <br />0.258 hours <br />0.00154 weeks <br />3.53865e-4 months <br />, the area inside the enclosed pipe galley was inspected to determine if evidence of a UF release was evident. During the inspection a small amount of hydrolyzed UF, 6
(UO F ) contamination was observed on the outside surface of block valve SMDB-2, an isolation 2 2 valve at withdrawal position #2. It was determined that the valve was the likely cause of the CADP actuations previously believed to be spurious. On April 27,1998, at 1036 hours0.012 days <br />0.288 hours <br />0.00171 weeks <br />3.94198e-4 months <br />, the PSS declared Tails withdrawal position #2 inoperable.
The outgassing was similar to the types ofleaks described in the Safety Analysis Report (SAR)
(Section 4.1.1.3.1) ';.nich states, "Small amounts of UF, and other toxic materials such a llF, CIF3 and UU F can be released during sampling operations, seal changes, failure to obtain sufficient cell 2 2 and piping UF negatives, ruptured copper tubing and pos<;ibly through buffer sytems. These 6
releases are prevented primarily by using engineering and administrative controls. To protect the operator in the unlikely event a release does occur, operation specifications require that personnel performing operations and maintenance, where the possibility of release exist, wear protective i
equipment such as an individually fitted gas mask. Releases in these cases may mean that few grams l
of UF will escape to the atmosphere. There are no system (Safety Systems) to prevent the release of UF while performing these types of operations. Engineering and administrative controls are l
6 considered adequate."
Valve SMDB-2 and the two CADP smoke detectors that alarmed are located inside an enclosed pipe galley. During the outgassing personnel were not exposed to UFs smoke. During the valve outgassing the smoke discharged from the valve was contained within the enclosed pipe galleys and
GDP 98-2051 Page 2 of 4 Event Report 98-06 Revision I the airborne alpha detector located outside the enclosed pipe galley did not alarm.
The valve designated as SMDB-2 is a 1-inch, screwed bonnet, metal to metal seat, globe valve. The valve is an "S" type manually operated valve, manufactured by the Crane Company. These valves are used throughout the cascade on feed, withdrawal, exhaust and auxiliary systems. Since replacement valves and subassemblies have not been available from the manufacturer for 40 years, plant personnel have routinely rebuilt, inspected and installed replacement subassemblies in the "S" type valves. Approximately 20 subassemblies are rebuilt and installed each year. A review of problem reports for the past two years found no evidence of UFs outgassings from "S" type valves.
According to the SAR for the Portsmouth Gaseous Diffusion Plant, the CADP smoke detectors are part of the UF detection alarm system and are classified as a Q safety system when monitoring 6
equipment operating above atmospheric pressure. In this instance, the monitored equipment was operating above atmospheric pressure. This CADP smoke detector actuation is reportable in accordance with SAR, Section 6.9 Table 6.9-1, J (2).
Cause of Event The direu cause fbr the CADP UF Smoke Detection System actuation was an outgassing of UF, 6
from valve SMDB-2. While in withdrawal mode the valve is maintained in the "open" position. The valve is turned to the " closed" po.sition when the system is isolated for service / repair.
On March 31, 1998, approximately one month belbre the outgassing, maintenance personnel replaced the valve subassembly in valve SMDB-2. The replacement subassembly was rebuilt and QC inspected in the X-720 Ilydro Shop. The QC inspection perfbrmed in the hydro shop on March 31,1998, verified there was no le.2kage between the outer and inner valve bellows assembly. The QC hydro shop inspection will not detect a leak between the bonnet and the valve body. This inspection can only be perfbrmed af ter the subassembly is installed in the valve as part of field Post i
Maintenance Testing (PMT). On April 1,1998, Ibilowing installation of the valve subassembly, j
Cascade Operations performed (PMT) to verify the valve was not leaking.
On June 16,1998, the valve subassembly was rer.oved from the valve. During removal it was l
observed that the subassembly was looser than expected. It was also noticed that two aluminum gaskets had been installed between the valve body and the subassembly bonnet. According to the manufacture's drawing only one gasket should have been installed. The gasket is a soft aluminum i
washer that deforms upon tightening of the bonnet threads to the valve body. A circumferential
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groove in the bonnet allows for the deformation of the gasket material into a positive seal that prevents the flow of UF, into the space inside the yoke (beil) of the valve exposed to atmosphere.
!!nclosureI GDP 98-2051 Page 3 of 4 Event Report 98-06 Revision I With two gaskets in place there is not a positive seal since there exists an additional flat aluminum i
to aluminum surface between the two gaskets.
i It was determined that the outgassing was caused by a breech of the seal between the bonnet and valve body caused by the installation of a second aluminum gasket. The second gasket provided an i
additional path for the flow of the UF out of the valve body to atmosphere.
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The root cause of the outgassing was an error in the work instructions used by the maintenance personnel to perform the valve subassembly replacement. The error lead to a misinterpretation of i
how many gaskets was to be installed between the bonnet and the valve bady. The work package i
instructions stated, " install new subassemMy and gaskets as directed." The instructions used the i
plural noun " gaskets" and not singular noun " gasket." Since two gaskets were supplied with the rebuilt valve subassembly and no other directions were given, the personnel performing the work i
installed both gaskets.
1 It was determined through intersiews with the X-330 Maintenance Section Manager, the First Line i
Manager (FLM) and maintenance personnel that this was an isolated incident. There is no indication i
that other valve assemblies were installed using two gaskets. A search of the database for the past i
three years showed no other outgassings from these typ.6 of vah es.
i Corrective Actions 1.
By September 30,1998, Cascade Operations will ensure the valve subassembly is removed from the valve.
2.
By October 30, 1998, I?ngineering will perfo*m an inspection of the failed valve subassembly.
3.
By November 20,1998, based on the results of the valve inspection, !!ngineering will determine appropriate corrective actions.
4.
On June 30,1998, the work instructions were proceduralized. The procedure clarifies that
- one new dead soft aluminum gasket is inserted between bonnet and valve body.
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Extent of Exposure ofIndividuals to Radiation or Radioactive Materials i
j There were no exposures to individuals from this incident to radiation or radioactive materials.
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GDP 98-2051 Page 4 of 4 Event Report 98-06 Revision i Lessons Learned from the Event There were no lessons learned from this event. Operators responded to this event in accordance with i
plant policies and procedures. No outgassing was observed. The release was small and could only i
be detected by the smoke detector and verified by the observation of hydrolyzed UF on the surface i
of the block valve.
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GDP 98-2051 Page1of1.
Event Report 98-06 List of Commitments 1.
By September 30,1998, Cascade Operations will ensure the valve subassembly is removed from the valve.
2.
.By October 30, 1998 Engineering will. perform an inspection of the failed valve -
subassembly.
3.
By November 20,1998, based on the result of the valve inspection, Engineering will determine appropriate corrective actions.
4.
On June 30,1998, the. work instructions were proceduralized. The procedure clarifies that i
one new dead soft aluminum gasket is inserted between bonnet and valve body, i
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