ML20198P620
| ML20198P620 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 11/03/1997 |
| From: | Polston S UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-97-1042, NUDOCS 9711070250 | |
| Download: ML20198P620 (4) | |
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Unclassified
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Ian. $02 441.%01 Nr. ember 3,1997 United States Nuclear Regulatory Commission SERIAL: GDP 97-1042 Attention: Document Control Desk Washington, DC 2055-001 Paducah Gaseous Diffusion Plant (PGDP)- Docket No. 70-7001 - Event Report ER-97-17 Pursuant to the Safety Analysis Report (SAR), Section 6.9, Table 1, Criteria J2, Attachment 1 is the required 30-day written Event Repon covering ER 97-17. This event involves the actuation of a Process Gas Leak Detector (PGLD) head as a result of a leak of uranium hexnfluoride (UF,,).
The Nuclear Regulatory Commission (NRC) was notified of the event on October 7,1997, (NRC No. 33038). Investigation activities we continuing with an estimated " final report" submission date of November 25,1997.
- Should you require furthet :nformation on this subject, please contact llill Sykes at (502)441 6796.
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UNCLASSIFIED
Unclassified Docket No. 70-7001 Page1of3 EVENT REPORT ER-97-17 BACKGROUND Cascade feed cylinders are transported to the cascade feed facilities in C-333 A and C-337-A.
The cascade feed vaporization involves heating the cylinders in steam-heated containment-type autoclaves to convert the solidified uranium hexafluoride U, 6 to liquid with a relatively high vapor pressure. The pressurized vapor is drawn off and controlled by valves and fbw-measuring devices to maintain distribution of UF gas through heated piping to appropriate points in the 6
enrichment cascade. Although the autoclaves are designed to contain a UF. release, Process Gas Leak Detector (PGLD) heads are installed above the autoclave head locking ring, the heated housing at the autoclave head, above the jet station piping, in the piping trench, and on the west wall in C-337-A. If a leak is detected, an alarm is sounded in the autoclave area and on the UF6 detector alarm panel in the Operations Monitoring Room (OMR).
On October 6,1997, a small UF. leak occurred on the purge air pressure bleed line on autoclave 3 South at the C-333-A feed facility. As a result of the leak, PGLD head YE-613-13, which is a "Q" safety system located in the autoclave housing, alarmed. The 3 South autoclave and five other in service autoclaves in C-333-A were placed into containment, the piping was evacuated below atmosphere and the piping leak was temporarily plugged.
The automatic actuation of a "Q" safety system resulting from a valid condition is reportable in accordance with Safety Analysis Report (SAR), Section 6.9, Table 1, Criteria J2. On October 7,1997, the Nuclear Regulatory Commission (NRC) headquarters was notified of the event (Event No. 33038).
DESCRIPTION OF EVENT On October 6,1997, at 3:40 p.m. the C-333 A position 3 South PGLD head (YE-613-13) fired.
The operators responded in accordance with the alarm response procedure (CP4-CO-AR8333 A),
and emergency procedure (CP4-CO-CE5017A), donned their protective suits and took hydrogen fluoride (IlF) samples. None of the samples indicated the presence ofIIF. An atteenpt was made to reset the PGLD head; however, the attempt was unsuccessful. At 4:10 p.m. a smoke watch was established and at 4:25 p.m., YE-613-13 was declared inoperable. At 4:35 p.m. additional troubleshooting reported the presence of smoke from a small pin hole leak from a three-eighths inch copper purge line. The area was immediately evacuated of all personnel and the operations supervisor and Plant Shift Superintendent (PSS) were notified. At 4:54 p.m. the C-333 A
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- Docket No. 70-7001 Page 2 0f 3 autoclaves were placed into the containment mode. At 5:05 p.m. the Plant Emergency Squad was called out to report to C-333-A, position 3 South for a small UF. release. The Emergency Squad took additional air samples, which were negative, and plugged the source of the UF. leak.
At 7:45 p.m. the "all clear" was given. At 10:25 p.m. the C-333-A position 3 South was declared inoperable, due to the release from the purge line. At 11:00 p.m. position 3 South was placed in mode 2 and the smoke watch terminated.
On July 15,1996, an Engineering Service Order (ESO) Z96880 was devcloped to install pressure bleed points on select system piping to allow for full differential pressure testing of all autoclave containment block valves during autoclave containment testing. At the time, the existing autoclave configuration did not allow for full testing of outer autoclave containment valves.
A tap and valve was added at three places on piping at each autoclave to allow back-pressure to be relieved for containment valve testing on 22 autoclaves. On December 18,1996, modification work was completed on autoclave position 3 South. Pressure was initially raised on the line to 110 pounds psig. The pressure was then reduced to 100 psig, a soap test perfonned, and no leaks were evident.
Troubleshooting indicates that the leak occurred in a copper line whkh was instalicd in accordance with ESO Z96880. The line is located between the purge containment valve (CV 511) and the purge valve (CV 512). The purpose of the copper line is to bleed off pressure between CV 511 and CV 512 for pressure decay tests. Laboratory analysis of the copper piping has not been completed. Copper is considered compatible with UF.; therefore, the presence of UF. would not cause a deterioration of the copper. Additionally, there have not been other leaks from copper piping installed on the other 21 autoclaves as a part of the improved containment testing modifications that were not discovered during installation testing.
CAUSE OF EVENT A. Direct Cause The direct cause of the actuation of PGLD head YE-613-13 was the release of UF. from the copper piping.
IL Root Cause The root cause of the actuation of the PGLD head YE-613-13 and subsequent UF. release has not been determined, initial reports indicated the existence of a pin hole in the piping. However, subsequent preliminary laboratory analysis has not confinned the source of the leak. A similar problem has not occurred in the remaining 21 autoclaves which underwent identical modifications.
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Dc:ket No. 70-7001 Page 3 of 3 C. Contributing Cause To be determined.
CORRECTIVE ACTIONS A. Completed Corrective Actions
- 1. On October 7,199h autoclave 3 South was declared inoperable and placed into mode 2.
- 2. On October 22,1997, the copper piping was sent to the plant laboratory for analysis.
B. Planned Corrective Actions To be determined.
LESSONS LEARNED To be detennined.
EXTENT OF EXPOSURE OF INDIVIDUALS TO RADIOACTIVE MATERIALS Two operators and one instrument mechanic had urine bioassay results of 4,14, and 15, respectively, micrograms of uranium per liter. When retested, the results were less than MDA (less than 3 micrograms of uranium per liter), and below the follow-up recall limit of 5 micrograms of uranium per liter. The intake from the event was not significant and well below regulatory limits.
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