ML20211D975
| ML20211D975 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 08/20/1999 |
| From: | Pulley H UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-99-1026, NUDOCS 9908270176 | |
| Download: ML20211D975 (4) | |
Text
-
.r.
' d USEC f
A Global Energy Company August 20,1999 l
]
GDP 99-1026 j
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, Rev.1 Pursuant to 10CFR76.120(d)(2), enclosed is the revised final written event report pertaining to l the unplanned actuation of the C-333-A autoclave 1 North autoclave steam pressure control i
system (ASPCS) on June 23,1999. The Nuclear Regulatory Commission Headquarters (NRC-l HQ) operations office was notified of the initial event on June 24,1999 (NRC No. 35855). The l
initial report submitted on July 23,1999 has been revised to include the root and contributing cauxs.
Any questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
Sincerely, I
kwa
- ey General Manager l
Paducah Gaseous Diffusion Plant
Enclosures:
As Stated cc: NRC Region III Office NRC Resident. inspector - PGDP l
4fld I
i 270,257 i
l 9908270176 990820 PDR ADOCK 07007001 C
PDR j
P.O. Box 1410, Paducah, KY 42001 Telephone 502-441-5803 Fax 502441-5801 hnp://www.uscc.com Offices in 1.ivermore, CA Paducah, KY Portsmouth, OH Washinpon. DC
n-Docket 70-7001 GDP 99-1026 Page1of3 EVENT REPORT ER-99-11, Rev.1 l
DESCRIPTION OF EVENT 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 i
(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
' 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 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 11 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 metal seating surfaces were worn to a point where accurate steam control would be decreased.
j LL
c; _
i l? l Docket 70-7001 GDP 99-1026 Page 2 of 3 The safety risk significance of this type of event is low, due to the design 'of ASPCS and other
- 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 / pressure. For both channels, the alarm and actuation occurs at s8 psig and isolates the steam supply by closing the block valves located on either side of the subject steam control
(
valve. These isolation valves are subjected to periodic leak testing prescribed in the TSR. In the l i
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.
l A. Direct Cause l
l l
The direct cause of the unplanned actuation is attributed to the inability of the autoclave I
temperature control valve to properly control the amount of steam being admitted into the autoclave.
1 B. Contributing Cause l
e The facility operators less than adequate recognition of and reaction to the rising autoclave steam pressure has been identified as a contributing cause of this event.
There is no requirement to constantly monitor the autoclave pressures, the procedure does establish normal operating parameters which are to be maintained. A review of available autoclave and cylinder pressure recorder data indicates that, in this case, there was sufficient time and 6pportunity for the operators to notice and react to the rising autoclave pressure.
This conclusion is based on the fact that the operators did notice and reacted appropriately to a rise in the cylinder pressure by performing an evacuation process, per procedure, to reduce the cylinder pressure. During the cylinder evacuation operation, the operators are required to monitor the cylinder pressure for at least one minute. The cylinder and autoclave pressures are displayed on a digital LED readout gauge at the autoclave. At the time the cylinder pressure was being monitored, the autoclave pressure was approximately 6 psig. In this case, the pressure was rising slowly enough for the operators to take action and bring the pressure under control. This inattention to detail is being addressed via crew briefings with all qualified operators at C-360, C-333-A and C-337-A. All other personnel will be given this briefing prior to returning to work in these areas.
r:
r Docket 70-7001 GDP 99-1026 Page 3 of 3 C. Root Cause The root cause is attributed to an end-of-life failure of the steam pressure control valve. As stated previously, this valve has been in service approximately ten years. This is the first I
reported event caused by this type of steam control valve failure. Given the relatively low safety significant of this event and the absence of an adverse trend related to this type of steam control valve failure, further corrective action is not warranted at this time.
CORRECTIVE ACTIONS
- A. Completed Corrective Actions
- 1. On July 8,1999, the autoclave 1 North steam control valve was replaced.
- 2. A crew briefing was held with qualified operators C-360, C-333-A and C-337-A personnel to reinforce management expectations related to monitoring of operational parameters. A crew briefing deficiency form has been filed to' ensure that all off-site personnel will receive this briefing upon their return to work.
B. Planned Corrective Actions None l
EXTENT OF EXPOSURE OF INDIVIDUALS TO RADIATION OR RADIOACTIVE MATERIAL l
None i
LESSONS LEARNED l
Autoclave operational parameters must be closely monitored and actions taken when equipment failures occur.
1 l
l