ENS 43232
ENS Event | |
|---|---|
03:00 Sep 23, 2006 | |
| Title | Reported Under Nrc Bulletin 91-01 24 Hour Notification |
| Event Description | On September 22, 2006, during a heavy rain storm, the water level in the C-310 position #4 scale pit reached 3 5/8 inches (3.625 inches). The scale pit liquid sensor alarm system did not function as credited, in violation of NCSA 310-004. The water was found by operators by visual inspection. NCSA 310-004 credits the liquid sensor alarm to provide notification of water in the pit in excess of 2.5 inches.
At the time of the event, the water level was measured to be less than 3 5/8 inches (3.625 inches) deep. However, subsequent measurements accounting for slope in the scale pit floor show that the water could actually have been as deep as 4 3/8 inches (4.375 inches). The two process conditions relied upon for double contingency are mass and geometry. The first leg of double contingency is based on preventing a release of fissile material containing greater than a safe mass of uranium from getting into the scale pits. This is controlled through reliance on the integrity of the UF6 cylinder, liquid UF6 piping, pigtail, and liquid UF6 handling equipment. Since a UF6 release containing greater than a safe mass has not occurred, the mass parameter has been maintained Therefore, this leg of double contingency is maintained. The second leg of double contingency relies on the scale pit liquid sensor alarm system to provide notification of water in the pit in excess of 2.5 inches. Requiring the liquid sensor to alarm at 2.5 inches allows ample time to react and prevent the accumulation of more than 3.68 inches water. Although the alarm system did not function, operators performed a surveillance of the scale pits and identified water in the #4 scale pit in excess of 2.5 inches. NCSE 032 shows that the 'subcritical' slab height of UO2F2 solution in the C-310 scale pit is 4.1 inches at (deleted) wt% U235. The NCSE determined that an unsafe geometry slab height (is., greater than 4.1 inches) cannot form if the initial water height is less than 3.6 inches. The as-found water height corrected for the scale pit slope was determined to be as deep as 4 3/8 inches (4.375 inches). Therefore, the parameter limit specified in NCSE 032 was exceeded and double contingency was not maintained. The NRC Senior Resident Inspector has been notified of this event. PGDP Problem Report No. ATRC-06-3103; PGDP Event Report No. PAD-2007-01: NRC Worksheet No. SAFETY SIGNIFICANCE OF EVENTS: Although the scale pit liquid sensor alarm system failed to alarm when water in the pit exceeded 2.5 inches, an insufficient amount of water was available to achieve a criticality. The assay of the product withdrawal system at the time of the event was less than (deleted) wt%. Additional KENO and bucking calculations were included in design analysis calculation to illustrate the margin of conservatism. Those calculations show that the scale pit would have remained below the PGDP USL even for UO2F2 slab heights up to 7.75 inches at (deleted) wt%. In addition, a UF6 release containing greater than a safe mass did not occur. POTENTIAL CRITICALITY PATHWAYS INVOLVED: In order for criticality to be possible, a large UF6 release containing greater than a critical mass of uranium would have to form in the scale pit, and the pit would have to contain a sufficient amount of water. CONTROLLED PARAMETERS: The two process conditions relied upon for double contingency are mass and geometry. ESTIMATED AMOUNT, ENRICHMENT, FORM OF LICENSED MATERIAL: Product withdrawal assay at the time of the event was less than (deleted) wt% U235. However, no UF6 release occurred. CORRECTIVE ACTIONS TO RESTORE SAFETY SYSTEMS AND WHEN EACH WAS IMPLEMENTED: All C-310 scale pit sensor alarming systems have been repaired and verified to work properly and put back in service. The NRC Resident Inspector was notified of this report. |
| Where | |
|---|---|
| Paducah Gaseous Diffusion Plant Paducah, Kentucky (NRC Region 2) | |
| License number: | GDP-1 |
| Reporting | |
| Response | |
| Time - Person (Reporting Time:+4116.73 h171.53 days <br />24.504 weeks <br />5.639 months <br />) | |
| Opened: | Tony Hudson 15:44 Mar 13, 2007 |
| NRC Officer: | John Mackinnon |
| Last Updated: | Mar 13, 2007 |
| 43232 - NRC Website | |
Paducah Gaseous Diffusion Plant with Response | |
WEEKMONTHYEARENS 483982012-10-10T18:05:00010 October 2012 18:05:00
[Table view]Response Double Contingency Control for Empty Cylinders Not Maintained ENS 479112012-05-08T21:16:0008 May 2012 21:16:00 10 CFR 76.120(c)(2), Response Autoclave High Pressure Isolation System Failure ENS 474832011-11-28T15:30:00028 November 2011 15:30:00 Response 24-Hour Report Concerning a Localized Loss of a Geometry Criticality Control Contingency ENS 473102011-09-30T13:54:00030 September 2011 13:54:00 Response 24-Hour Nrc Bulletin 91-01 Report Involving a Loss of One Leg of Double Contingency ENS 471762011-08-19T13:15:00019 August 2011 13:15:00 Response 24-Hr Loss of Criticality Control Report Required Under Bulletin 91-01, Supplement 1 ENS 465922011-02-03T15:30:0003 February 2011 15:30:00 Response 24 Hour Notification Under Bulletin 91-01 Concerning Leakage of Moderating Liquid ENS 463122010-10-06T16:06:0006 October 2010 16:06:00 Response 24 Hour Notification Under Bulletin 91-01 Concerning Cooldown Verification of Uf6 Cylinders ENS 461052010-07-17T19:07:00017 July 2010 19:07:00 Response 24 Hour 91-01 Bulletin Report on Loss of One of Two Criticality Control Contingencies ENS 454922009-11-12T17:15:00012 November 2009 17:15:00 Response Violation of a Nuclear Criticality Safety Control ENS 450422009-05-04T10:07:0004 May 2009 10:07:00 Response 24 Hour 91-01 Bulletin Report on Loss of One of Two Criticality Control Contingencies ENS 445582008-10-09T20:37:0009 October 2008 20:37:00 Response 24-Hours Bulletin 91-01 Report Involving Failure to Visually Inspect Storage Cylinders ENS 442232008-05-18T22:21:00018 May 2008 22:21:00 Response Violation of a Nuclear Criticality Safety Approval - 24-Hour Report ENS 441512008-04-17T21:44:00017 April 2008 21:44:00 Response 24-Hour Nrc Bulletin 91-01 Report Involving an Excessively Large Container Found in a Fissile Control Area ENS 441002008-03-26T19:57:00026 March 2008 19:57:00 Response 24 Hour Report of Degraded Criticality Control ENS 440562008-03-11T19:57:00011 March 2008 19:57:00 Response Two Cylinders Identified with Weight Change Prior to Wash ENS 432322006-09-23T03:00:00023 September 2006 03:00:00 Response Reported Under Nrc Bulletin 91-01 24 Hour Notification ENS 421652005-11-22T18:05:00022 November 2005 18:05:00 Response Improper Criticality Spacing for Waste Drum ENS 411582004-10-29T14:45:00029 October 2004 14:45:00 Response Criticality Control Report ENS 410202004-09-04T18:45:0004 September 2004 18:45:00 Response Violation of Nuclear Criticality Safety Control in the Process Building ENS 408732004-07-14T18:00:00014 July 2004 18:00:00 Response Criticality Control 24-Hour (Bulletin 91-01) Report ENS 408602004-07-08T20:50:0008 July 2004 20:50:00 Response 24 Hour Nrc Bulletin 91-01 Loss of Criticality Control ENS 407232004-05-03T21:00:0003 May 2004 21:00:00 Response Criticality Control 24-Hour (Bulletin 91-01) Report ENS 407002004-04-23T13:45:00023 April 2004 13:45:00 Response Criticality Control 24-Hour (Bulletin 91-01) Report ENS 408052004-04-23T10:53:00023 April 2004 10:53:00 Response Paducah Gaseous Diffussion Plant - Response Bulletin 91-01 24 - Hour Report ENS 406412004-04-04T19:30:0004 April 2004 19:30:00 Response 24-Hour Nrc Bulletin 91-01 Loss of Criticality Control Notification ENS 404552004-01-16T21:27:00016 January 2004 21:27:00 Response 24 Hour Notification for Bulletin 91-01 Loss of Criticality Safety Controls Involving Waste Drum ENS 404472004-01-13T19:00:00013 January 2004 19:00:00 Response 24 Hour Notification for Bulletin 91-01 Loss of Criticality Safety Controls Involving Waste Drum ENS 403562003-11-25T09:45:00025 November 2003 09:45:00 Response 24 Hour Nrc Bulletin 91-01 Notification Regarding Loss of Double Contingency Protection ENS 401512003-09-11T13:45:00011 September 2003 13:45:00 Response Double Contingency Was Not Maintained for Non-Fissile Nams. ENS 401392003-09-07T12:50:0007 September 2003 12:50:00 Response Criticality Controls Degradation at Paducah ENS 401092003-08-27T14:00:00027 August 2003 14:00:00 Response Procedural Deficiency Omission 2012-05-08T21:16:00 | |