ML20195C958
| ML20195C958 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 11/11/1998 |
| From: | Pulley H UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-1073, NUDOCS 9811170253 | |
| Download: ML20195C958 (6) | |
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e USEC A GW Energ Company November 11,1998 GDP 98-1073 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-98-25
. Pursuant to 10CFR76.120(d)(2), enclosed is the required 30-day written report for the steam leak on the No. 2 North Autoclave in the C-333-A feed facility. This was initially reported on October 14,1998 (NRC No. 34913).
Commitments contained in this submittal are identified in Enclosure 2. Any questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
Sincerely, o
ulley General Manager Paducah Gaseous Diffusion Plant
Enclosure:
As Stated cc: NRC Region III Office NRC Resident Inspector - PGDP i
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9811170253 981111 y.
PDR ADOCK 07007001 C
PDR; J
PO. Box 1410, Paducah, KY 42001 j
Telephone 502-441-5803 Fax 502-441-5801 http://www.usec.com l
Offices in Livermore, CA Paducah, KY Portsmouth OH Washington, DC i
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l Docket No. 70-7001 I
- GDP 98-1073 Page1of4 EVENT REPORT ER-98-25 DESCRIPTION OF EVENT l
On October 13,1998, at 2243 hours0.026 days <br />0.623 hours <br />0.00371 weeks <br />8.534615e-4 months <br />, an operator discovered a small quantity of steam leaking from l
the head-to-shell interface on the No. 2 North Autoclave in the C-333-A Feed Facility. The cylinder in the autoclave was in the heeling process (TSR Mode 5) at the time of discovery. The Plant Shift Superintendent (PSS) was notified who declared the No. 2 North Autoclave High Pressure Isolation (AHPI) system inoperable. The autoclave wasjetted and placed in TSR Mode 2 (Out of Service),
in accordance with Technical Safety Requirement (TSR) 2.2.3.1.C. When the shell was opened, the
- o-ring, which provides the seal between the autoclave head and shell, was found to be protruding out of the autoclave head groove at the 10 o' clock position.- The protruding section was j
l appmximately 9 inches in length and had been crushed toward the inner side of the autoclave head.
The o-ring is part of the containment boundary of the AHPI system which is required to be operable when the autoclave is in Mode 5 by TSR Limiting Condition for Operation LCO 2.2.3.1.
On October 14,1998, at 0907 hours0.0105 days <br />0.252 hours <br />0.0015 weeks <br />3.451135e-4 months <br />, the PSS notified the Nuclear Regulatory Commission (NRC) of the event, pursuant to 10 CFR 76.120(c) (2). NRC assigned Worksheet No. 34913 to the event notification.
1 An event investigation team was formed to determine the root cause. The o-ring was removed and L
analyzed by the Plant Laboratory. The analysis indicated that the o-ring conformed to the l
specifications ofits Engineering Specification Data Sheet (ESDS), DS-CMD-16289-115, Rev. O.
Infrared analysis was used to verify the o-ring material was ethylene propylene, as specified on the ESDS. Hardness measurements were taken on the undamaged portion of the o-ring which matched the ESDS specification for a Durometer hardness of 70. The o-ring was measured and met the ESDS specification 'for mean diameter. The o-ring cross section diameter measurements were l
determined to be typical for an o-ring which had been compressed during autoclave heating cycles.
L Prior to the steam leak, the subject o-ring had experienced 15 heating cycles since being installed on September 15,1998. Prior to installation, the o-ring had passed inspection by Quality Control
. under Inspection Plan 07-999-9153. Additionally, prior to placing in service, the No. 2 North Autoclave, with this o-ring installed, had passed an autoclave head-to-shell alignment test and a
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pressure decay test.
The Plant Laboratory also measured the thickness of various damaged areas of the o-ring. These L
measurements indicated that the o-ring was not in the o-ring gasket groove when the autoclave shell l
was closed and was crushed between the head and shell by the closing / locking process. When the j
damaged o-ring was removed from the groove for laboratory analysis, no debris was found under the o-ring. No damage was found to the o-ring gasket groove nor was there any evidence of sticking on the mating surface. No lubricant was apparent on the o-ring. The laboratory analysis was documented in detail in KY/L-2038," Failure of C-333-A Autoclave No. 2 North."
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3 Docket No. 70-7001 GDP 98-1073 Page 2 of 4 -
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l Operations personnel indicated that approximately one month before the steam leak, an eight-to ten-
' inch section of the o-ring on the No. 2 North Autoclave had protruded out of the groove between the 9 o' clock and 12 o' clock positions. This was observedjust prior to a pressure decay test. The front line manager was contacted who instmeted the operators to push it back into the groove, which j
they did. The investigation team could not definitively conclude through interviews and review of a
documentation whether the o-ring with the previously observed extrusion was the same o-ring which experienced the steam leak.
l CAUSES OF EVENT
- A.
Direct Cause l
The direct cause of the steam leak on the No. 2 North Autoclave was the failure of the o-ring
- to provide an adequate seal between the autoclave head and shell, due to its damage condition.
l B.
Root Cause L
The root cause of the damaged o-ring was determined to be related to o-ring installation L
practices which did not evenly distribute the tension over the o-ring surface. This conclusion was based on the following factors. The o-ring conformed with Engineering specifications.
There was no evidence of any foreign material pressuring the o-ring from the groove.
i Measurements of the o-ring gasket groove were within acceptable values. An o-ring was L
previously observed protruding from the groove. Additionally, the system engineer has been
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consulted several times within the last year concerning problems experienced during o-ring installations. In these problem installations, fitting the o-ring in the groove, by procedure, sometimes resulted in an excess amount of o-ring material that would not easily fit in the groove. This can be attributed to the stretching of the o-ring during the installation process.
i C.
- Contributing Cause I
A contributing cause of this event is an inadequate inspection of the o-ring prior to closing the autoclave shell. In this event, the lab analysis of the damaged o-ring indicates the o-ring would have had to be protruding out of the groovejust prior to closing the autoclave shell, but was not noticed by the attending operator.
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e Docket No. 70-7001 GDP 98-1073 Page 3 of 4 CORRECTIVE ACTIONS
. A. Corrective Actions Taken 1.
On October 16,1998, Maintenance replaced the o-ring on the No. 2 North Autoclave in the C-333-A Feed Facility.
2.
On October 16,1998, Operations performed the pressure decay test on the No. 2 North Autoclave. The test results were acceptable and the autoclave was declared operable by the PSS on October 20,1998.
'3.
On November 11, 1998, Maintenance revised and implemented CP3-GP-OP4109,
" Alignment Check of UF Autoclave Head to Shell,0-Ring Check and Replacement, rmd 6
Knife Switch Stop Block Check and Repair," to give more detailed guidance on installing o-rings in autoclaves. The procedum revision requires the maintenance mechanic to insta!1 the o-ring, beginning at the 6 o' clock position. The o-ring is then worked into the groove l
on the left and right sides, meeting at the 12 o' clock position, while distributing the slack evenly around the groove. Additionally, the procedure was revised (a) to allow the mechanic to use a lubricant such as clean tap water or petroleum-free wire pulling soap, if necessary, to promote more even distribution of o-ring tension; and '(b) to instruct the i
mechanic to contact the front line manager if o-ring extrusions occur. All Maintenance mechanics who install o-rings in autoclaves will be instructed on this revised installation process via a pre-job briefing.
B.
Corrective Actions Planned 1.
By December 11,1998, Operations will conduct crew briefings with operators in C-333-A, l
C-337-A, and C-360 related to this event (ER-98-25) and the recommended actions for gasket inspections.
- 2. - By January 15,1999, Operations will revise CP4-CO-CN2045a," Operation of the C-333 A and C-337A Vaporizer Facilities," and CP4-CO-CN2051a, "C-360 Autoclave Loading and Heating," to improve o-ring inspection requirements. The procedure revision will include L
the requirement to inspect the entire o-ring to ensure that the o-ring is not damaged or protruding out of the groove, prior to loading the cylinder in the autoclave. If any o-ring is damaged or is protruding from the groove, the operator will be instructed to contact the front line manager who will contact the systems / shift engineer. This revised inspection L
practice will be reviewed with operators through crew briefings prior to the effective date of the procedures. Also, a similar revision requirement will be placed against procedure CP4-CO-CN2051j," Transferring UF at C-360." This procedure is currently "On Hold,"
6 but would need the same changes prior to being released.
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Docket No. 70-7001 GDP 98-1073 Page 4 of 4 EXTENT OF EXPOSURE OF INDIVIDUALS TO RADIATION OR TO RADIOACTIVE MATERIALS Then: was no exposure of any individuals to radiation or to radioactive materials, as a result of this event. The event only involved the release of a small amount of steam from the autoclave.
LESSONS LEARNED Uneven distribution of the tension in o-rings during o ring installation can create excessive stress in the o-ring that could cause the o-ring to protrude out of the groove, thereby subjecting it to damage during closing of the autoclave and creating the potential for a breach of the containment boundary of the AHPI system.
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Docket No. 70-7001 GDP 98-1073 Page1ofI List of Commitments Event Report ER-98-25 1.
By December 11,1998, Operations will conduct crew briefings with operators in C-333-A, C-337-A, and C-360 related to this event (ER-98-25) and the recommended actions for gasket inspections.
2.
By January 15,1999, Operations will revise CP4-CO-CN2045a, " Operation of the C-333 A and C-337A Vaporizer Facilities,"and CP4 CO-CN2051a,"C-360 Autoclave Loading and Heating," to improve o-ring inspection requirements. The procedure revision will include the requirement to inspect the entire o-ring to ensure that the o-ring is not damaged or protruding out of the groove, prior to loading the cylinder in the autoclave. If any o-ring is damaged or is protruding from the groove, the operator will be instructed to contact the front line manager who will contact the systems / shift engineer. This revised inspection practice will be reviewed with operators through crew briefings prior to the effective date of the procedures. Also, a similar revision requirement will be placed against procedure CP4-CO-CN2051)," Transferring UF at C-360." This procedure is currently "On Hold," but 6
would need the same changes prior to being released.
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