ML20205F494
| ML20205F494 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 03/29/1999 |
| From: | Jonathan Brown UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-99-2009, NUDOCS 9904060279 | |
| Download: ML20205F494 (4) | |
Text
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USEC A Global Energy Company i
March 29,1999 GDP 99-2009 l
U. S. Nuclear Regulatory Commission j
. Attention: Document Control Desk Washington, D.C. 20555-0001 l
J Portsmouth Gaseous Diffusion Plant (PORTS)
Docket No. 70-7002 Event Report 98-15, Revision 1 Pursuant to 10CFR 76.120(d)(2), Enclosure 1 provides a revised 30-day written Event Report for an event involving the failure of an Autoclave Viton 0-Ring at the Portsmouth Gaseous Diffusion Plant. The revised event report includes the root cause and corrective actions. Changes from the previous report arc marked with a vertical line in the right margin. 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,
/
. Morris Brown General Manager Portsmouth Gaseous DifTusion Plant
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Enclosures:
As Stated cc:
NRC Region III Office NRC Resident Inspectors - PORTS 9904060279 990329 3
PDR ADOCK 07007002 j
C PDR 2
06'4 no. sox soo. Portsmouth, ori 45c6i Telephone 614-897-2255 Fax 614-897-2644 http://www.usec.com OfTices in Livermore, CA Paducah, KY Portsmouth, OH Washington. DC c
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GDP 99-2009 Page 1 of 2
. Event Report 98-15, Revision 1
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Description of Event On November 23,1998, at approximately 0600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br />, X-344 Autoclave (AC) #2 was in Mode II, heating a 48" Uranium Ilexaflouride cylinder, when an operator heard air leaking from the autoclave.
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Although the autoclave was operating with steam, no visible steam leakage was observed. After l~
noting that air was leaking from the twelve o' clock position c. ts cr: dave shell, the operator
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l placed AC #2 in Mode VII (shutdown). The autoclave shell s as opened and the operator noticed l
a gap between the two ends of the Viton 0-ring at the splie J joint. Aller removal of the cylinder from the autoclave, an as-found pressure decay test was performed to the requirements of Technical l
Safety Requirement (TSR) SR 2.1.3.5.3. The test concluded the autoclave leakage exceeded the l
allowed leakage. This event is repe-table as a. safety system failure in accordance with l
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l Cause of Event The direct caitse for the air leakage on AC #2 was separation of the Viton 0-ring at the splice joint.
l The gap in the 0-ring measured approximately 3/16".
l The Viton 0-ring is used to seal the autoclave head and shell mating surfaces. The 0-ring fits into l
a machined groove in the autoclave head. The 0-ring is made from Viton cord stock which is cut to l
fit and spliced together with glue. When the shell is fully closed, a locking ring draws the shell and l
head together to compress the O-ring and create a pressure seal.
l The root cause for the 0-ringjoint separation was a misalignment between the autoclave shell and j
head. An inspection of the autoclave shell to head alignment revealed that the center line of the shell l
and head mating surfaces were not parallel. With the vessel closed, the shell ar.d head of the l
autoclave made contact near the 10:30 position, while a gap of approximately 5/16" existed near the i
4:30 position. A test was conducted by performing several autoclave steam runs and vessel closures l
without a cylinder. During the testing the O-ring shifted downward approximately 1/8" toward the l
10:30 position. It is believed that this movement of the 0-ring demonstrated that the head and shell l
misalignment created axial tension on the 0-ring joint which resulted in 0-ring separation.
l An alignment inspection of ten of the remaining twelve autoclaves has been performed. None of l these autoclaves were discovered to have a misalignment of the head and shell that would place the l
O-ringjoint under tension. The two autoclaves which have not been inspected, X-344 AC #4 and l
X-343 AC #7, are currently out of service as part of the Autoclave Nuclear Safety Upgrade Project.
l These autoclaves will be checked for shell and head misalignment prior to being returned to service.
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'a GDF 99-2009 Page 2 of 2 Event Report 98-15, Revision 1 Corrective Actions 3
1.
On November 30,1998, the Viton 0-ring was replaced on AC #2.
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On January 30,1999, the head and shell of X-344 AC #2 was realigned.
l 3.
By October 31,1999, a periodic inspection of the autoclave head to shell alignment will be l
incorporated into the plant's preventive maintenance schedule.
l Extent of Exposure ofIndividuals to Radiation or Radioactive Materials 1
There was no release of radioactive material during this event.
l Lessons Learned Improper autoclave shell to head alignment can create sufficient axial force on the 0-rings to cause l
the 0-ring splice joint to separate.
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GDP 99-2009 Page1of1 Event Report 98-15, Revision 1 List of Commitments 1.
By October 31,1999, a periodic inspection of the autoclave head to shell alignment will be l
incorporated into the plant's preventive maintenance schedule.
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- Regulatory commitments contained in this document are listed here. Other actions listed in this submittal are not l
considered regulatory commitments in that they are either stat:ments or actions completed, or they are considered enhancements to USEC's investigation, procedures, or operations.
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