ML20249C483
| ML20249C483 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 06/25/1998 |
| From: | Pulley H UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-1050, NUDOCS 9806300111 | |
| Download: ML20249C483 (6) | |
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f TUSEC A Global Energy Company June 25,1998 GDP 98-1050 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-98-17 Pursuant to Safety Analysis Report, Table 6.9-1, Criteria J.2, enclosed is the required 30-day written report for the actuation of the UF release detection system in C-310-A. This was initially reported 6
on May 27,1998 (NRC No. 34292).
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.
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Paducah Gaseous Diffusion Plant
Enclosures:
As Stated cc:
NRC Region 111 Office NRC Resident Inspector - PGDP fh
--. n 9906300111 980625 PDR ADOCK 07007001' C
PDR i l
I!O. Box 1410. Paducah, KY 42001 Telephone 502 441-5803 Fax 502-441-5801 http://www.uer. em Offices in Livermore, CA Paducah, KY Portsmouth, Oil Washic.gton, DC
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Docket No. 70-7001 GDP 98-1050 Page1of4 EVENT REPORT ER-98-17 DESCRIPTION OF EVENT On May 26,1998, at 1610 hrs., a UF release occurred in C-310-A from breaks in a %-inch copper 6
tubing instrument line associated with a 4-inch G-17 gate valve, EDX-1. The instrument line is part 1
of a pressure system used to determine if a leak is occurring between the valve seats of EDX-1. The release ocurred during valving operations associated with placing the West Nonnetex withdrawal i
pump online. As the operator began to open valve EDX-2, he saw a puff of smoke from EDX-1 I
valve and immediately closed EDX-2 valve. Personnel in C-310-A followed the "see and flee" l
policy and exited the building. The Plant Shift Superintendent was notified of the release. The plant emergency squad was called out; the first entry team entered C-310-A at 1654 hrs. During the
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emergency response, one of the entry team members bumped the instrument line associated with i
EDX-1, increasing the UF release. At 1700 hrs., a UF release detection system alarm was received 6
6 in the C-310 Area Control Room, as a result ofdetector head YE-48 8 actuatmg. In accordance with Safety Analysis Report, Table 6.9-1, Criteria J.2, the Nuclear Regulatory Commission (NRC) was notified of this safety system actuation on May 27,1998 (R-ference NRC Notification Worksheet l
No. 34292).
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.CAUSES OF EVENT l
A. Direct Cause The release occurred from two cracks in the %-inch copper tubing instrument line. The instrument line, which was approximately three to four feet in length, extended from EDX-1 valve, out through the cell housing and was terminated by a pressure gauge. A small %-inch gauge isolation valve, commonly referred to as a p-nut valve, was located in the instrument line approximately seven inches below the pressure gauge. Additionally, the instre nent line had a coupling approximately five inches above the valve port of EDX 1 valve.
Two failures in the instrument line occurred. The first failure occurred at a bend in the tubing, approximately %-inch below the p-nut valve, close to the point where the copper tubing extends through the cell housing. The second failure in the tubing occurred at a sharp bend near the point the tubing enters the valve body.
l The tubing was analyzed by the Plant Laboratory to determine the cause of failure. A scanning l
electron microsecpe (SEM) image of the failure surface indicated that the wall of the instrument line had not significantly thinned from corrosion or stretching. The SEM image also showed a t
Docket No. 70-7001 l
GDP 98-1050 l
Page 2 of 4 flat surface around most of the circumference of the tubing which i; typical of fatigue. The cause of the first failure was determined by the Plant Laboratory to be a fatigue crack which l
initiated on the inside bend of the tubing directly below the p-nut valve. The surface of the first 1
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failure was close to the point where the copper tubing extended through the cell housing and
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showed signs of scarring, indicating that the instrument line had made contact with the cell j
housing. The instrument 8.ine was subject to significant vibration and was not secured in any
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manner. This kind of damage can initiate a fatigue crack. The pressure gauge overhung the p-l
-nut valve by approximately seven inches. This configuration, coupled with the vibration, L
introduced a cyclic bending force sufficient to accelerate the fatigue crack. Additionally, the j
sharp bend in the instrument line caused " work hardening" of the tubing material, making this section more susceptible to fatigue.
The second failure of the tubing occurred at a sharp (almost 180 ) bend near the point the instrument line entered the valve body. The SEM image of the surface of the second failure
. point showed the tube was flattened in the direction of the sharp bend, with the crack being 3
perpendicular to the bending direction. This failure was determined by the Plant Laboratory to be caused by excessive bending. This conclusion was confirmed by observing the fracture I
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surface of a piece of new %-inch copper tubing that had been bent until it failed and noting the similar features. Tests were also performed which showed that the tubing had not become embrittled during' service.
B. Root Cause-p The root cause of this event was poor installation practices related to the routing, securing, and bending of the copper tubing instrument line. This is evidenced by the unsupported instrument.
line which is subject to significant vibration and sustained damage as it made contact with the cell housing. Additionally, the sharp bends in the line are not an acceptable maintenance practice and do not reflect the use of a tube bender for installation, as good maintenance practice would expect. These bends caused work hardening of the material and increased the likelihood offailure.
The instrument line was likely installed over ten years ago. Improved maintenance practices and
. rigorous work control requirements currently in place should prevent similar occurrences in today's environment...Under current maintenance work practices, an installation of this type
. would be controlled by a Q-level work package and would require the maintenance supervisor to inspect the work. Additionally, hiring practices in recent years for instrument mechanics have been to hire trained and experienced First and Second Class Instrument Mechanics, rather than trainees, as was done ten years ago. The practices related to installing tubing are considered
" skill of the craft" If a mechanic exhibited a weakness in this skill, the ut line manager
- inspecting the work would ensure remediation occurred.
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Docket No. 70-7001 l
GDP 981050 Page 3 of 4 To address the generic issue, a walk-down will be completed by Systems Engineering to inspect the installation of %-inch copper tubing instrument lines associated with Q piping in areas which operate above atmosphen: and experience a similar level of vibration. Areas meeting this criteria are in buildings C-310 and C-315 between the Normetex discharge and the condensers.
Corrective Action Planned No. I reflects a walk-down of these areas by Systems Engineering l
to identify any deficiencies in the installation of %-inch copper tubing instrument lines. Work l
requests will be issued by Operations to address any deficiencies identified (Corrective Action Planned No. 2).
CORRECTIVE ACTIONS A.
Corrective Actions Planned l
- 1. By August 27,1998, Systems Engineering will perform a walk-down in C-310 and C-315 to inspect installations ofinstrument tubing associated with Q-piping in areas which are subject to significant vibration and operate above atmospheric pressure. Scope of the walk-down in C-310 and C-315 will be between the Normetex discharge and the condensers. A listing of all deficiencies identified will be supplied to Operations.
2 By September 30,1998, Operations will issue work requests to address the deficiencies identified in Corrective Action No.1.
EXTENT OF EXPOSURE OF INDIVIDUALS TO RADIATION OR TO RADIOACTIVE
" MATERIALS Four operators who were in the area of the release had positive bioassay for uranium with all samples being above the plant's initial action level of 5 pg/L. One of the operators had a result above the restriction level of 40 pg/L with the result being 42 pg/L. Follow-up recall samples were obtained on the personnel. The uranium intakes and associated dose relative to the release were not significant and were well below regulatory limits and plant administrative control levels.
Preliminary dose estimates indicate intakes were less than 1 mg. and associated doses less than 5 mrem committed effective dose equivalent.
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GDP 98-1050 Page 4 of 4 l
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LESSONS LEARNED l
1 The integrity ofinstrument lines which were installed in the past under less stringent maintenance I
practices and work control and which are subject to significant vibration may be compromised, allowing a release of UF. under above-atmospheric conditions.
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Docket No. 70-7001 GDP 98-1050 Page1of1 List of Commitments Event Report ER-98-17 l
- 1. By August 27,1998, Systems Engineering will perform a walk-down in C-310 and C-315 to inspect installations ofinstrument tubing associated with Q-piping in areas which are subject to significant vibration and operate above atmospheric pressure. Scope of the walk-down in C-310 and C-315 will be between the Normetex discharge and the condensers. A listing of all deficiencies identified will be supplied to Operations.
2 By September 30, 1998, Operations will issue work requests to address the deficiencies identified in Corrective Action No.1.
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