ML20210E429
| ML20210E429 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 07/23/1999 |
| From: | Pulley H UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-99-1022, NUDOCS 9907280220 | |
| Download: ML20210E429 (3) | |
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. A Global Energy Company July 23,1999 GDP 99-1022 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-99-11 Pursuant to 10CFR76.120(d)(2), enclosed is the required 30-day written event report pertaining to the unplanned actuation of the C-333-A autoclave 1 North autoclave steam pressure control system (ASPCS) on June 23,1999. The Nuclear Regulatory Commission Headquarters (NRC-HQ) operations office was notified of the initial event on June 24,1999 (NRC No. 35855). The investigation to determine the root cause of this event is ongoing, but has not been completed.
This report will be revised when the investigation is completed and a target date of August 30, 1999, has been established for the revision.
Any questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
Sincerely, 9/ _
N Howard Pulley General Manager Paducah Gaseous Diffusion Plant
Enclosures:
As Stated l
cc: NRC Region III Office NRC Resident Inspector - PGDP i
p b '7 P I
9907200220 990723 PDR ADOCK 07007001
' avu47 P.O. Box 1410, Paducah, KY 42001 l
Telephone $02-441-5803 Fax 502-441-5801 http://www.usec.com OfTices in Livermore, CA Paducah, KY Portsmouth, OH Washington, DC t
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Docket 70-7001 GDP 99-1022 Page1of2 EVENT REPORT ER-99-11 DESCRIPTION OF EVENT i
i At 2050 hours0.0237 days <br />0.569 hours <br />0.00339 weeks <br />7.80025e-4 months <br /> on June 23,1999, an automatic high autoclave steam pressure control system (ASPCS) actuation occurred on autoclave position 1 North in the C-333-A feed vaporization facility. At the time of the actuation the autoclave had been in Technical Safety Requirement (TSR) Mode 5 (heating) for approximately three hours with no abnormal conditions noted by i
. facility operators. The actuation of the ASPCS caused the closure of the steam inlet block valves and the vent line isolation valve at approximately 7 psig, as designed, and placed the autoclave in a safe condition. Facility operators followed alarm response procedures and placed the autoclave in TSR Mode 2 (open).
The Plant Shift Superintendent (PSS) was immediately notified of the actuation and declared the ASPCS inoperable.
At 0418 hours0.00484 days <br />0.116 hours <br />6.911376e-4 weeks <br />1.59049e-4 months <br /> on June 24,1999, the Nuclear Regulatory Commission Headquarters (NRC-HQ) operations office was verbally notified of the event in accordance with the PGDP SAR 6.9 l
Table-1, criteria J.2.
CAUSE FOR THE EVENT Testing of the_ autoclave pressure / temperature control system indicated that all control loop instrumentation was operating properly, but the temperature control valve (TCV-523) was found to be leaking across the seats and was unable to properly control the amount of steam being admitted into the autoclave. This allowed the autoclave steam pressure to rise to the ASPCS actuation set point.
This valve is installed between two autoclave steam containment block valves and is not relied upon to provide autoclave steam isolation function. Since the valve is located within the autoclave containment boundary, it is specified as a "Q" safety class component. Its only safety function is to prevent an atmospheric release of UF6 and water reaction products from its body, installation flanges, etc. The valve is a 2-inch "CamFlex II Series 35002" control valve manufactured by Masoneilan/ Dresser Corporation rated at 250 psig. The subject valve has been in service approximately 10 years. This is the first known event caused by this type of failure.
The valve has been removed from the system and an inspection of the valve concluded that the 4
metal seating surfaces were worn to a point where accurate steam control would be decreased.
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Docket 70-7001 GDP 99-1022 Page 2 of 2 The safety risk significance of this type of event is low, due to the design of ASPCS and other L autoclave safety systems, which would preclude exceeding the autoclave safety limits.
The autoclave steam pressure control system has two channels, at which increasing pressure in the autoclaves will isolate the steam supply before exceeding the safety limit for cylinder temperature /pmssure. For both channels, the alarm and actuation occurs at 58 psig and isolates the steam supply by closing the block valves located on either side of the subject steam control valve. In the event this system fails, a high-pressure isolation system actuation occurs at s 15 psig and places the autoclave into full containment.~~ The autoclave shell-pressure safety limit is 220 psig.
I A. Direct Cause The direct cause of the unplanned actuation is attributed to the inability of the autoclave temperature control valve to properly control the amount of steam being admitted into the autoclave.
B. Root Cause
' The investigation to determine the root cause of this unplann::d actuation has not been completed and other factors which may have precluded this event are being evaluated.
CORRECTIVE ACTIONS A. Completed Corrective Actions
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- 1. On July 8,1999, the autoclave 1 North steam control valve was replaced.
B. Planned Corrective Actions To be determined.
EXTENT OF EXPOSURE OF INDIVIDUALS TO RADIATION OR RADIOACTIVE l
MATERIAL None LESSONS LEARNED To be determined.