ML20217K595
| ML20217K595 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 03/30/1998 |
| From: | Polston S UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-1021, NUDOCS 9804070271 | |
| Download: ML20217K595 (4) | |
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USEC A Global Energy Company March 30,1998 GDP 98-1021 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-98-05 Pursuant to 10 CFR 76.120(d)(2), enclosed is the required 30-day written report for the loss of the UF release detection system in C-333-A. This was initially reported on March 6,1998 (NRC No.
33852).
Any questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
- Kmcerely, 1
Steve Polston General Manager Paducah Gaseous Diffusion Plant Enclosures cc:
NRC RegionIII OiTice NRC Resident Inspector-PGDP 9804070271 900330 PDR ADOCK 07007001
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C PDR 1e W PO. Ilos 1410, Paducah, KY 42001 F
Telephone 502-441-5803 Fax 502-441-5801 hrrp://www.usec.com l
Oflices in Livermore, CA Paducah, KY Portsmouth,011 Washington, DC
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Docket No. 70-7001
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GDP 98-1021
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Page1of3 EVENT REPORT ER-98-05 l
DESCRIPTION OF EVENT The UF. release detection system for C-333-A consists of a number ofionization chamber smoke X
detectors located above autoclave locking rings, in autoclave instrument heated housings, in the piping trench, and at the feedjet station. These detectors are monitored for actuations or trouble by -
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. a panel in the local Operations Monitoring Room (OMR). This panel provides local alarms in the L
' OMR and provides an input to the programmable logic controller (PLC) for autoclave position 1.
This PLC initiates audible and visual alarms in the local autoclave area, the C-333 Area Control l'
Room (ACR), and the C-300 Central Control Facility (CCF). The alarms for these areas are l
considered part of the safety function of the UF release detection system.
6 On March 1,1998, at appmximately 1015, the PLC for C-333-A autoclave position I went into halt mode. This actual.ed the containment safety systems for the Nos.1 North and 1 South autoclaves which were both feeding UF at the time. When the processor halted, the ' audible and visual alarms for the UF. release detection system were lost in the local autoclave area, the C-333 ACR, and the C-300 CCF. The alarm in the OMR was not lost. This resulted in the inoperability of a safety
. system that was required by Technical Safety Requirement 2.2.4.1 to be available and operable, since other autoclaves in C-333-A were in a mode which required the UF, release detection system
' to be operable.-
To d-? m.h the cause of the PLC halt, troubleshooting was performed by the system engineer and :
' maintenance personnel. Troulleshooting detennined that a single bit in memory had changed ~
causing the PLC to go into halt mode. This was identified by comparing the PLC program in memory following the PLC halt with a controlled copy of the PLC program. This comparison showed that a single bit had changed at Rung No. 370. The controlled copy of the program was reinstalled on the PLC. The installed copy was then successfully verified against the controlled copy. A f-+ianal test of the PLC was successfully performed which involved actuation of the UF.
release detection' system.
The event was' discussed with the vendor, Square D, and operating parameters, such as the power
. supply voltage, were evaluated and determined to be within vendor recommended guidelines.
System Engineering determined, with the concurrence of the vendor, that the cause of this memory j
change was random, electrical noise. Proper grounding and mounting within a metal cabinet are part i
! of the_ current design and comply with the manufacturer's recommendations for minimization of e
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- noise effects.L The manufacturer recommended the PLC be reprogrammed and allowed to operate l-for o'ne to two weeksi This period of time is considered sufficient to determine that there is no hardware failure associated with the software change. The PLC (which diagnostically checks its
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Docket No. 70-7001 GDP 98-1021 Page 2 0f 3 configuration approximately 5 times per second) has not exhibited any problems since the software program was reinstalled on March 9,1998.
- CAUSES OF EVENT A.'
. Direct Cause The direct cause of the inoperability of the PGLD system was the PLC going into halt mode which disabled the audible and visual alarms in the local autoclave area, the C-300 CCF, and q
the C-333 ACR, B.
Root Cause
~ The root cause ofthe PLC going into hah mode was random noise which resulted in a single memory bit changing. This occurrence was a " soft error" and was recoverable by simply
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reprogramming the processor and reloading the software. This unexpected, random 4
electrical noise was not preventable by following the standard installation practices. No record of similar failures was found for the 11 years that the PLCs in this application have I
been in service.~ There are no generic implications to this event; and the risk associated with -
reoccunence is small, because local OMR annunciation ofleak detection alarms remains functional throughout the event.
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' CORRECTIVE ACTIONS A. Corrective Actions Taken 1.
On March 9,1998, post maintenance testing was successfully completed on the C-333-A
' PLC No.1, following reprogramming and re-installation of software.-
B.. Corrective Actions Planned y
None EXTENT OF EXPOSURE OF' INDIVIDUALS TO RADIATION ~ OR TO RADIO /
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- MATERIALS No exposure ofindividuals to radiation or radioactive materials occurred during this event, since there was not a release of any material.
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Docket No. 70-7001
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L GDP 98-1021 Page 3 of 3 LESSONS LEARNED i
'Ihis problem of random noise causing the PLC to go into halt mode has been entered into the.
Business Prioritization System (BPS) for future tracking and trending.
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