ML20217R027
| ML20217R027 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 05/04/1998 |
| From: | Polston S UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-1029, NUDOCS 9805130095 | |
| Download: ML20217R027 (4) | |
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' s r ESEC p9 A Global Energy Company May 4,1998 GDP 98-1029 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-98-01, Rev. 2 Pursuant to SAR Section 6.9, Table 1, Criteria J.2, enclosed is the required 30-day written event repon covering the actuation of the autoclave position 2 East, steam pressure control safety system in Building C-337-A. The Nuclear Regulatory Commission (NRC) was notified of the event on January 13,1998 (NRC No. 33521). An interim report relative to this event was provided to NRC on February 11,1998.
On February 1,1998, a secon6 event occurred involving the position 2 East, steam pressure control safety system in building C-337 A. NRC was notified of this event on February 2,1998 (NRC No.
33637). An interim report relative to the second event was provided to NRC on March 2,1998.
On March 20,1998, Revision 1 to the investigation was provided to NRC, which combined the two event investigations above and advised that the determination of the root cause was continuing.
This report updates information submitted on March 20,1998, Revision 1. Changes to the report are annotated by vertical lines in the right margin of this report. The determination of a root cause is continuing. A revised report is planned for submission by July 24,1998.
Am questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
S' cerely, N
Steve Polston General Manager Paducah Gaseous Diffusion Plant 9805130095 980504
Enclosures:
As Stated PDR ADOCK 07007001
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C PDR cc:
NRC Region III Office NRC Senior Resident Inspector, PGDP P.O. Box 1410, Paducah, KY 42001
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Telephone 502-4415803 Fax 502-441-5801 http://www.usec.com Offices in thermore, CA Paducah, KY Portsmouth, OH Washington, DC D 0s a
Enclosure !
Docket No. 70-7001 GDP 98-1029 Page1of3 EVENT REPORT ER-98-01, Rev. 2 DESCRIPTION OF EVENT This report provides information for two events (NRC No. 33521; 33637) related to malftmetions of the autoclave steam pressure / temperature control loop instrumentation.
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In addition to the event reports due to safety system actuations, some related problems that are similar, but which did not result in reportable safety system actuations due to operator recognition a
nnd intervention are included in efforts to find the root cause.
The autoclaves were considered operable, even though the condition was recuvig. The failures are 1
self-revealing and the pressure control system has two independent channels (P-514 and P-515) at which increasing pressure in the autoclaves will isolate the steam supply, before exceeding the safety limit for cylinder temperature / pressure. The first alarm an 1 actuation occurs at < 8 psig and only isolates the steam supply. The second alami and actuation puts Ue autoclave into full containment i
at < 15 psig. The autoclave shell pressure safety limit is 220 psig.
On January 12,1998, autoclave position 2 East, Building C-337-A was being retumed to operation j
after previously being, declared inoperable on January 2,1998, because of a limit switch failure on j
the head-to-shell closure. Following the maintenance work to repair the limit switch, a successful
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post-maintenance test was conducted. On January 12,1998, at 1508 hrs., the Phnt Shift 4
Superintendent (PSS) declared autoclave position 2 East operational. At 1705 hrs., the autoclave
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was placed into service with the steam controller in automatic. At 1710 hrs., the autoclave pressure
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increased to approximately 7 psig, a high autoclave steam pressure alarm was received in the Operations Monitoring Room (OMR) and the steam pressure control system actuated as designed.
The primary and secondary steam controllers were on automatic; the steam pressure digital reading was -3.75 psig on the steam controller; the strip chart recorder read approximately 6.5 psig (alarm set-point range 6.5 psig-7.5 psig); and the control valve was fully open. At 1755 hrs., according to procedure, the cylinder valve was closed and purged; the autoclave was jetted and opened; and the pigtail was disconnected. At 1825 hrs., autoclave position 2 East was removed from service (Mode 2). In summary, the steam pressure in the autoclave had increased to the alarm set-point, due to a malfunction in the steam pressure / temperature controlloop and actuated the steam pressure control safety system as designed. All safety system components performed as designed to place the autoclave in a safe condition. On January 13,1998, at 0325 the Nuclear Regulatory Commission Headquarters Operations (NRC-HQ) office was notif4d of this event, in accordance with Safety Analysis Report (SAR) Section 6.9, Table 1, Criteria J.2.
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I Enclosure !
Docket No. 70 7001 GDP 98-102S Page 2 of 3 l
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An event investigation team was assigned to determine the root cause for the steem pressure / temperature control safety system actuation. The strip chart for autoclave position 2 East, l
which records the auteclave pressure, cylinder pressure and autoclave temperature indicated that 3
prior to the shutdown for maintenance, the steam pressure controller was controlhng the steam within acceptable limits. The chart also indicated that during this event, the pressure in the autoclave mse to the alarm set-point (approximately 7 psig), at which the steam pressure control safety system actuated, closing the steam isolation valves and the thetmovent block valves.
s Indications at this time were that a 6-pin connecter and/or in-line amplifier in the P-515 pressure
!oop was failing in a manner that changed the steam pressure being sensed by the controller for the steam comrol valve. On January 22,1998, after replacing suspected defective components, autociave position 2 East, Building C-337-A was declared operable.
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On February 1,1998, at 1920 hrs., the autoclave steam pressure increased to approximately 7 psig on position 2 East, Building C-337-A. The associated alarm was received in the OMR and the steam pressure control system actuated, as designed. The primary and secondary controllers were on automatic; the steam pressure digital reading was -3.75 psig on the steam controller; the strip chart recorder was approximmely 7 psig; and the control valve was fully open. This was very similar to the first event on January 12,1998. At 1950 hrs., the PSS declared autoclave position 2 East inoperable..At 2015 hrs., according to procedure, the cylinder valve was closed and purged; the pigtail was disconnected afterjetting and opening the autoclave; and the position was removed frem service (Mode 2). In summary, a malfunction of the steam pressure / temperature control loop instrumentation caused the steam pressure in the autoclave to increase to the ahtrm set-point (approximately 7 psig), which resulted in an actuation of the steam pressure control safety system.
On February 2,1998, at 0736 hrs., NRC-HQ office was notified of the event in accordance with SAR, Section 6.9, Table 1, Criteria J2 (see NRC No. 33637).
On February 11,1998, after replacing a transducer suspected of failing and successfully completmg post-maintenance testing, autoclave 2 East, Building C-337-A was declared operable.
In addition to the two reportable events, eight incidents involving erroneous demand signals to the l
steam controller are included in the investigation. Neither the reportable events, nor the non-reportable incidents challenged the 15 p.;ig safet.y system setting.
The investigation is focused on new in-line amplifiers, cables, pressure transducers and 6-pin connectors that were installed as part of the Instrument Upgrade Project (IUP) and have been in service since October 1997. These components were satisfactorily tested prior to making the autoclaves operable after the IUP.
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Docket No. 70-7001 i
GDP 98-1029 Pace 3 of 3 t
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Components suspected of failure were es. 'aated, both destructively and nondestructively and the
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supplier was involved in the evaluation of the transducers.
1 On March 30 and 31,1998, representatives from the Paducah Gasecus Diffusion Plant (PGDP)
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l observed the destructive analysis of two "Sensotec," model P30P, transducers that had failed. The l
I analysis was performed in "Sensotec's" Laboratory, it was determined that the failure of the two l
tonsducers was due to electrical short circuits between the transducers internal wire and casing. A l
conclusion by "Sensotec" relative to what precipitated the electrical short circuits is not supported l
by tests conducted by PGDP's Instrument Shop and Laboratory. Additional tests are on-going at l
1 PGDP to determine the root cause for the failures. Reporting requirements in accordance with l
l 10CFR21 continue to be considered.
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CAUSE OLEyENE I
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Direct Cause 1
Being determined l
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