ML20199E231
| ML20199E231 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 11/17/1997 |
| From: | Morgan J UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-97-2031, NUDOCS 9711210129 | |
| Download: ML20199E231 (4) | |
Text
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(Jnit:0 St in Enrich sent Corporttion 2 Democracy Carit:t T-6903 'iocueoga on,.
Betheada.MD 2001r Tel: (301)564 3200 Far (301) 564 3201 November 17,1997 United States Nuclear Regulatory Commission GDP 97 2031 Attention: Document Control Desk Washington, D.C. 20555 0001 Portsmouth Gaseous Diffusion Plant (PORTS)- Docket No. 70-7002 - Event Report 97-20 Pursuant to the Safety Analysis Report (SAR), Section 6.9, Table 6.91, J (2), Enclosure 1 is the required 30 day written Event Report for an occurrence involving the actuation of the autoclave shell high pressure containment shutdown safety system in the X-343 Building at the Ponsmouth Gaseous Diffusion Plant. Investigation activities are continuing to determine the root cause and corrective actions for this event. This report will be revised fvilowing completion of these activities. The revised report is tcheduled for January 16,1998. There are no new commitments contained in the report.
Should you require additional information regarding this event, please contact Scott Scholl at (614)897 2373.
Sincerely, Y h' James B. Morgan Acting General Manager Portsmouth Gaseous DiiTusion Plant DIA:SScholl:kpb Qh; I
Enclosores t
ec:
D. Hartiend, NRC Resident inspector, PORTS NRC Region 111.
9711P.10129 971117 PDR ADOCK O?Ov7002 C
'iVb1I he in Uvermore.Califomia Paducah, Kentucky Portsmouth, ONo Washington, DC
Docket.No. 70 7002
!!nclosure1 Page 1 of 3 Event Report 97 20 Description of Event On October 18,1997, at 1645 hours0.019 days <br />0.457 hours <br />0.00272 weeks <br />6.259225e-4 months <br />, X 343 autoclave #4 was in Mode IV, feeding a Uranium llexafluoride (UF.) cylinder to the enrichment cascade, when an audible and visual ulann for steam shutdown was received. Operators responding to the alarm found that the autoclave shell high pressure containment shutdown safety system (AS11PCS) had actuated. The internal autoclave 1,ressure observed by the operators was 22.3 psia. TSR 2.1.3.5 lists the limiting control setting (LCS) for ASIIPCS as 15 psig, though it has been conservatively set at 8.0 psig (22.45 psla), which is the sarac set point as the autoclave shell high steam pressure shutdown safety system (ASilSPS).
The operators followed the alann response procedures and determined that the ASilPCS alarmed when channel "A" of the two channel pressure sensing instrumentation actuated. The autoclave operators and the X 343 First Line Manager obtained autoclave condensate samples and verified that no UF. release had occurred. The t.atoclave alarms were reset aRer verifying that all containment valves had actuated as required. The autoclave was then opened and insoccted. No abnonnal conditions were identified.
Aner determining that the safety systems had functioned as designed and that there were no abnonnal conditions, operators closed the autoclave, restarted the steam and the cy!!nder feed cycle was continued. Autoclave operation continued without further incident until the following shin.
A decision was made by the Plant Shin Superintendent (PSS) on the following shin to shut the autoclave down at 2319 hours0.0268 days <br />0.644 hours <br />0.00383 weeks <br />8.823795e-4 months <br />. The PSS determined that the root cause of the ASilPCS safety system actuation had not been determined before the autoclave had been restarted and that it would be more conservative to shut down the autoclave until the cause of the actuations had been determined and corrected.
The cylinder was moved to a difTerent autoclave and the remainder of the UF. was fed to the cascade. There was no release of hazardous material or radiological exposures associated with this event. The actuation of the AsilPCS safety system is reportable in t., ordance with the Safety Analysis Report (SAR), Section 6.9 Table 6.91, J(2).
The ASilPCS is provided to shut o!Tthe steam supply and place the autoclave in containment in the event of a UF. release inside the autoclave, During a large release, a massive amount of hydrogen fluoride (llF) gas would be rapidly produced by the reaction of UF. with water. The llF gas would increase the pressure in the autoclave and upon the autoclave internal pressure reaching the ASilPCS setpoint, a tedundant pressure sensor would trigger containment shutdown. Safety systems in addition to the ASilPCS which prevent the cylinder high temperature safety lin it from being
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Docket No. 70 7002 Enclos6te 1 i
Page 2 of 3
< Event Report 97-20 j
reached include the autoclave shell high steam pressure shutdown and the UFicylinder high I
temperature autoclave steam shutoff.
Cause of Event The direct cause of the ASilPCS actuction on autoclave # 4 was a higher tlwa normal steam pressure inside the autoclave shell. 'Ihe cylinder had been heating for about thrce hours and the feed valve had been open for abov%n hour. The UF was being fed to t!.e cascade at a high flow rate. The high 6
vaporization rate lowered the cyl_inder temperature inside the autoelave to less than 200 F, which caused the steam regulator to switch to high steam loading pressure. Although the steam regulator i
is supposed to self regulate, the time lag between the increasing steam pressure and the self-regulating mechanism was long enough to allow the steam pressure to increase to 22.3 psia when
- it activated the ASilPCS safety system.
Engineering has not yet been able to determine the exact cause of the over pressurization. A test
. procedure is being developed to investigate the over pressure condition and to gather additional information to assist in determining the root cause. Autoclave #4 will not be used for feed and sampling operations until appropriate corrective actions are determined and implemented. This et ent report will be revised when the root cause and corrective actions have been determined. A revised report is scheduled for January 16,1998.
Corrrctive Actions Corrective actions will be provided with the final event report.
Extent of Exposure ofIndividuals to Radiation or Radioactive Materials L
? *Ihere were no exposures to individuals from this incident to radiation or radioactive materials.
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Docket No. 70 7002 Page 3 of 3 Lessons Learned The PORTS Quality Assurance Plan requires that conditions adverse to quality be identified and corrected as soon as practical. In tlw case of cafety system actuations, the cause of the condition is determined and corrective actions are taken to preclude recurrence. Based on the facts that this was an isolated occurrence, the safety system operated properly, the preswm setpoint was actuated solely by steam pressure (no UF. release involved), and the fact that the amoclave contained a hot liquid cylinder, the on-duty PSS felt it was safer to continue f:cding the cylinder to remove the liquid UF.
from the autoclave prior to taking the autoclave out of service for troubleshooting.
Although no recurrence of the event actually occurred, the possibility existed that a second steam pressure isolation might have occurred had the conditions causing the original isolation been duplicated. When the next shift assumed the watch they made the decision that the more conservative course of action would be to stop feeding and take the autoclave out of senice for testing.
'the lesson leamed from this event is that autoclave operations should not continue ibliowing safety system actuations until the cause of the actuation has been determined and corrected.
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