ML20236F291
| ML20236F291 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 06/29/1998 |
| From: | Pulley H UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| ER-98-15, GDP-98-1047, NUDOCS 9807020102 | |
| Download: ML20236F291 (3) | |
Text
, _ _
USEC A cioba en.rry cony.or 4
l June 29,1998 GDP 98-1047 4
l United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 Paducah Gaseous Diffusion Plant (PGDP)
Docket No. 70-7001-Event Report ER-98-15 Pursuant to SAR, Section 6.9, Table 1, Criteria J.2, enclosed is the required 30-day written Event
- Report covering the actuation of the autoclave position 4 North, steam pressure control safety system in Building C-333-A. The Nuclear Regulatory Conunission (NRC) was notified of the event on June 8,1998 (NRC No. 34360).
Any questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
Sincerely, Ioward Pulley -
General Manager Paducah Gaseous Diffusion Plant f
Enclosure:
As Stated
/
L cc: NRC Region III Office NRC Resident Inspector - PGDP
.; mi JJ.
t 9807020102 990629 3
PDR ADOCK 07007001 C
pg P.O. Box 1410, Paducah, KY 42001 Telephone 502-441-5803 Fax 502-441-5801 http://www.usec.com Offices in Livermore, CA Paducah, KY Portsmouth, OH Washington, DC L__
Docket No. 70-7001 l
GDP 98-1047 Page 1 of 2 EVENT REPORT ER-98-15 i
DESCRIPTION OF EVENT
.On June 7,1998, at approximately 2110 hrs., the autoclave steam pressure increased to approximately 7.14 psig on position 4 North, Building C-333-A. The associated alarm was received l
in the Operations Monitoring Room (OMR) and the steam pressure control safety system actuated, as designed. The primary and secondary controllers were on automatic; the strip chart recorder was
)
approximately 5.94 psig and the steam pressure digital reading was approximately 7.14 psig. The variation in strip chart and steam pressure digital readings is attributed to observations made at I
differing times prior to shutdown. At 2145 hrs., the Plant Shift Superintendent (PSS) declared autoclave position 4 North inoperable. The operators, according to procedure, closed and purged the cylinder valve; the pigtail was disconnected after jetting and opening the autoclave; and the position removed from service (Mode 2). All safety system components performed, as designed, j
to place the autoclave in a safe condition. Limiting Conditions for Operation (LCO) 2.2.3.lb was entered.' On J'me 8,1998, at 0214 hrs., Nuclear Regulatory Commission Headquarters (NRC-HQ) office was notified of the event in accordance with Safety Analysis Report (SA.R), Section 6.9, Table l
1, Criteria J2 (NRC No. 34360).
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An event investigating team was assigned to determine the root cause for the safety system actuation.
The strip chart for autoclave position 4 North which records the autoclave pressure, cylinder pressure, and autoclave temperature indicated that 15 minutes prior to shutdown the steam pressure controller was controlling the steam within acceptable limits. However, examination of the strip chart indicated that less than 15 minutes prior to shutdown the pressure in the autoclave rose to the alarm set-point (approximately 7 psig), at which time the steam pressure control safety system actuated closing the steem isolation valves and thermovent valves.
Troubleshooting determined that the valve controller temperature and pressure loop (T-523), which is a non-safety system, sent an electrical signal to the current-to-pressure transducer (TY-523b) to completely close the temperature control valve (TCV-523). The temperature control valve was not called upon to completely close, due to the current-to-pressure transducer being out of tolerance.
Because the temperature control valve was not entirely closed, steam was allowed to enter the l
autoclave. The current-to-pressure transducer was out of tolerance by.413 psig which precluded the temperature control valve from completely closing.
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Docket No. 70-7001 i
GDP 98-1047 Page 2 of 2 The cause for the as-found condition of the current-to-pressure transducer (TY-523b) could not be determined. However, a review of Commitment Management's electronic data base from 1990 to the present did not indicate adverse trending or generic problems relative to out-of-tolerance autoclave valve controller temperature and pressure loops (T-523), including current-to-pressure transducers (TY-523b). The autoclave valve controller temperature and pressure loop is calibrated annually according to procedure and established schedule, and was last calibrated prior to this event on December 15,1997. The absence of recurring or generic problems indicates that the scheduled annual calibration of the T-523 loop is sufficient.
CAUSE OF THE EVENT A. Direct Cause The direct cause of this event was steam from the temperature control valve entering into the autoclave. The steam entering the autoclave led to the actuation of the safety system.
B. Root Cause The root cause for this event was a failure of the current-to-pressure transducer (TY-523b) to completely close the temperature control valve (TCV-523). The failure to close entirely was due to the temperature control transducer being out of tolerance by.413 psig.
CORRECTIVE ACTIONS A. Completed Corrective Actions
- 1. On June 12,1998, the T-523 temperature and pressure loop was calibrated, and tested.
B. Planned Corrective Actions None EXTENT EXPOSURE OF INDIVIDUALS TO RADIATION OR RADIOACTIVE MATERIALS None LESSONS LEARNED None