ML20217E147
| ML20217E147 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 03/20/1998 |
| From: | Polston S UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-1016, NUDOCS 9803300393 | |
| Download: ML20217E147 (4) | |
Text
d USEC r
A Global Energy Company March 20,1998 -
GDP 98-1016 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.1 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 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 l !o. 33521). An interim report relative to this event was provided to NRC on February 11,1998. Changes to the interim report are annotated by vertical lines in the right margin of this report.
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On February 1,1998, a second 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.
Both events are addressed in this report. The determination of a root cause is continuing. A revised report is planned for submission by May 6,1998.
Any questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
Sincerely, 1)
Steve Polston General Manager
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Paducah Gaseous Diffusion Plant
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Enclosures:
As Stated-cc:
NRC Region III Office NRC Senior Resident Inspector, PGDP 9803300393 900320 9
PDR. ADOCK 070070007 C-PDRj P.O. Box 1410, Paducah, KY 42001 Telephone 502-441-5803 Fax 502-441-5801 hnpi//www.usec.com
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. Oflices in Livermore, CA Paduuh, KY Portsmouth, OH - Washington, DC R
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Docket No.'70-7001 -
GDP 98-0016 Page1of3 EVENT REPORT ER-98-01, Rev. I DESCRIPTION OF EVENT LThis report provides supplemental information for two events (NRC No. 33521; 33637), related to l
malfunctions of the autoclave steam pressure / temperature control loop instrumentation.
l In addition to the event reports due to safety system actuations, some related problems which are j
similar, but which did not result in safety system actuations due to operator recognition and l
intervention are included in efforts to find the root cause.
l The autoclaves are considered operable, even though the condition is recurring. The failures are self-l revealing and the pressure control system has two independent channels (P-514 and P-515) at which l
increasing pressure in the autoclaves will isolate the steam supply before exceeding the safety limit l
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. for cylinder temperature / pressure. The first alarm and actuation occurs at < 8 psig and only isolates l
the steam supply. The second alarm and actuation puts the autoclave into full containment at < 15 l
- psig. The autoclave shell pressure safety limit is 220 psig.
I I
On January 12,1998, autoclave position 2 East, Building C-337.A was being returned to operation after previously being declared inoperable on January 2,1998, becsuse of a limit switch failure on the head-to-shell closure. Following the maintenance work to repair tile limit switch, a successful post-maintenance test was conducted. On January 12,1998, at 1508 hrs., the Plant Shift Superintendent (PSS) declared autoclave position 2 East operational. At 1705 hrs., the autoclave l
was placed into service with the steam controller in automatic. At 1710 hrs., the autoclave pressure l
increased to approximately 7 psig, a high autoclave steam pressure alarm was received in the l
Operations Monitoring Room (OMR) and the steam pressure control system actuated as designed.
l 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 control loop and actuated the steam pressure control.
. safety system as designed. - All safety system components performed as designed to place the Lautoclave in a safe condition. On January 13,1998, at 0325 the Nuclear Regulatory Commission
'(NRC) Headquarters Operations office' was notified of this event, in accordance with Safety Analysis i Report (S AR) Section 6.9, Table 1, Criteria J.2
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Docket No~ 70-7001 GDP 98-0016 Page 2 of 3 An event investigation team was assigned to determine the root cause for the steam l-pressure / temperature control safety system actuation. The strip chart for autoclave position 2 East, l.
which records the autoclave pressure, cylinder pressure and autoclave temperature indicated that l
prior to the shutdown for maintenance, the steam pressure controller was controlling the steam - l within acceptable limits. The chart also indicated that during this event, the pressure in the autoclave l
rose to the alarm set-point (approximately 7 psig), at which the steam pressure control safety system ' l actuated, closing the steam isolation valves and the thermovent block valves.
l L Indications at this time were that a 6-pin connector and/or in-line amplifier in the P-515 pressure l
loop was failing in a manner that changed the steam pressure being sensed by the controller for the j
steam control valve. On January 22, 1998, after replacing suspected defective components, j
autoclave position 2 East, Building C-337-A was declared operable.
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'l On February 1,1998, at 1920 hrs the autoclave steam pressure increased to approximately 7 psig l
on position 2 East, Building C-337-A. The associated alarm was received in the OMR and the steam l
pressure control system actuated, as designed. The primary and secondary controllers were on l
automatic; the steam pressure digital reading was -3.75 psig on the steam controller; the strip chart l
recorder was approximately 7 psig; and the control valve was fully open. This was very similar to the first event on January 12,1998. At 1950, the PSS declared autoclave position 2 East inoperable.
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At 2015 hrs., according to procedure, the cylinder valve was closed and purged; the pigtail was l
disconnected after jetting and opening the autoclave; and the position was removed from service - l.
(Mode 2).
In summary, a malfunction of the steam pressure / temperature control loop l
' instrumentation caused the steam pressure in the autoclave to increase to the alarm set-point l
(approximately 7 psig), which resulted in an actuation of the steam pressure control safety system.
- On February 2,1998, at 0736 hrs. the NRC Headquarters Operatior.s office was notified of the event l
in accordance with SAR, Section 6.9, Table 1, Criteria J2 (see NRC No. 33637).
l I
On February 11,1998, after replacing a transducer suspected of failing and successfully completing l
post-maintenance testing, autoclave 2 East, Building C-337-A was declared operable.
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In addition to the two reportable events, five incidents involving erroneous demand signals to the l
steam controller are included in the investigation. Neither the reportable events nor the non-l reportable incidents have challenged the 15 psig safety system setting.
l I
The investigation is focusing on new in-line amplifiers, cables, pressure transducers and 6-pin l
connectors that were installed as part of the Instrument Upgrade Project (IUP) and have been in l
t service since October 1997. These components 'were satisfactorily tested prior to making the - l autoclaves operable after the IUP.
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Docket No. 70-7001 l
GDP 98-0016 l
Page 3 of 3 l
Components suspected of failure are being evaluated, both destructively and nondestructively and l
the supplier is being involved in the evaluation. As soon as the failure mechanism is identified, l
10CFR21 reporting requirements will be considered.
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l CAUSE OF EVENT l
l A.
Direct Cause l
l Being Determined l
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