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| Entered date | Event description | |
|---|---|---|
| ENS 44158 | 23 April 2008 08:45:00 | At 0900 CDT on 04-22-08, the Plant Shift Superintendent (PSS) was notified that the weight monitoring systems on vessels 2 on C-333 Unit 1 Cell 9, Unit 2 Cell 2, Unit 4 Cell 2 and Unit 4 Cell 9 freezer-sublimers showed weight changes when improperly installed steel angle supports welded to the vessel inlet piping were cut free. Each freezer sublimer vessel has a weight monitoring and trip system (high-high weight trip system) that prevents the over-filling of UF6 into the vessel. The high-high weight trip system is required by TSR 2.4.3.1 to prevent overfilling the freezer-sublimer vessels when in mode F/S 1 (freeze) or F/S 3 (cold standby). At the time of discovery, each freezer sublimer was in a non-applicable TSR mode F/S 6 (out-of-service). However, each freezer-sublimer has been routinely operated in TSR modes F/S 1 and F/S 3 over several years with the steel angle supports installed. The steel angle supports were likely installed to facilitate piping alignment during freezer-sublimer construction over fifteen years ago. The steel angle supports were not removed after construction. The presence of the steel angle supports may affect the performance the high-high weight trip system specified in TSR 2.4.3.1. All other installed freezer-sublimers were inspected and no additional steel angle supports were similarly connected. Engineering personnel are conducting a formal stress analysis to determine the stresses the steel supports may have had on the weight monitoring and trip system. There is no evidence that the weight limits specified in TSR 2.4.3.1 have been exceeded as a result of this issue. Pending further analysis, this event is conservatively being reported as a 24 hour event in accordance with 10 CFR 76.120(c)(2)(i). This is an event in which equipment is disabled or fails to function as designed when: a.) the equipment is required by a TSR to prevent releases, prevent exposures to radiation and radioactive materials exceeding specified limits, mitigate the consequences of an accident, or restore this facility to a pre-established safe condition after an accident; b.) the equipment is required by a TSR to be available and operable and either should have been operating or should have operated on demand, and c.) no redundant equipment is available and operable to perform the required safety function. PGDP Assessment and Tracking Report No. ATRC-08-l 183; PGDP Event Report No. PAD-2008-12; Worksheet No. 44158 The NRC Senior Resident Inspector has been notified of this event.
Retracted on 5/29/08, engineering calculations show that the error from the supports was less than the margin provided in the setpoint calculations. The licensee notified the NRC Resident Inspector. Notified the R2DO (Widman) and NMSS (Stablein). |
| ENS 42973 | 8 November 2006 10:56:00 | At 1607 on 11/7/2006, the Plant Shift Superintendent (PSS) was notified of a failure of the C-333 Unit 6 Cell 3 process gas leak detection (PGLD) system. C-333 operators were alerted to the Unit 6 Cell 3 PGLD failure by the receipt of an Area Control Room alarm. The operators responded to the Unit 6 Cell 3 cell panel and discovered that the PGLD system was inoperable. C-333 Unit 6 Cell 3 and associated piping were operating above atmospheric pressure (Cascade Mode 2) at the time of the PGLD failure. The operators initiated a continuous smoke watch of the area with lost PGLD coverage until the associated equipment and piping pressure was reduced below atmospheric pressure in accordance with TSR LCO 2.4.4.1. The PGLD system is required per TSR 2.4.4.1 to be operable when a cascade cell and associated piping is above atmospheric pressure (Cascade Mode 2). This event is reportable as a 24 hour event in accordance with 10CFR 76.120(c)(2)(i). This is an event in which equipment is disabled or fails to function as designed when: a.) the equipment is required by a TSR to prevent releases, prevent exposures to radiation and radioactive materials exceeding specified limits, mitigate the consequences of an accident, or restore this facility to a pre-established safe condition after an accident; b.) the equipment is required by a TSR to be available and operable and either should have been operating or should have operated on demand, and c.) no redundant equipment is available and operable to perform the required safety function. The NRC Senior Resident Inspector has been notified of this event. PGDP Problem Report No. ATRC-06-3679; PGDP Event Report No. PAD-2006-11; NRC Worksheet No. 42973. The licensee stated that the equipment and piping pressure was reduced in order to allow the process to continue operating in a condition where the PGLD system is not required to be operable. The licensee is investigating the cause of the failure but it is preliminarily believed to be a failure of an instrumentation power supply. |
| ENS 42972 | 8 November 2006 08:52:00 | At 0859 on 11/7/2006, the Plant Shift Superintendent (PSS) was notified of a failure of the C-337A process gas leak detector (PGLD) YE-613-21 to alarm during TSR (Technical Safety Requirements) surveillance 2.2.4.1-1. TSR surveillance 2.2.4.1-1 is a quarterly test to verify that the PGLD will detect a UF6 release, alarm, and alert personnel. PGLD YE-613-21 provides coverage for the north section of the facility UF6 piping trench. Staff review of the failure, suggest that PGLD YE-613-21 may have failed prior to being removed from service to perform the 11/7/06 TSR surveillance. PGLD YE-613-21 was replaced and tested satisfactorily. Additional testing and engineering review of PGLD YE-613-21 is being performed to ensure the operability of the PGLD and to develop any needed corrective actions. This event is reportable as a 24 hour event in accordance with 10CFR 76.120(c)(2)(i). This is an event in which equipment is disabled or fails to function as designed when: a.) the equipment is required by a TSR to prevent releases, prevent exposures to radiation and radioactive materials exceeding specified limits, mitigate the consequences of an accident, or restore this facility to a pre-established safe condition after an accident; b.) the equipment is required by a TSR to be available and operable and either should have been operating or should have operated on demand, and c.) no redundant equipment is available and operable to perform the required safety function. The NRC Senior Resident Inspector has been notified of this event. PGDP Problem Report No. ATRC-06-3670; PGDP Event Report No. PAD-2006-10; NRC Worksheet No. 42972. |
| ENS 40738 | 9 May 2004 20:48:00 | The following information was obtained by the regulatee via facsimile: At 0130 (hrs. CDT) on 05-09-04, the Plant Shift Superintendent (PSS) was notified of a failure of the C-316 High Voltage UF6 Release Detection System. The High Voltage UF6 detection system was disabled by a computer malfunction. This High Voltage UF6 Release System is designed to activate alarms in the event of a UF6 release. The PSS declared the system inoperable and TSR (Technical Safety Requirement) LCO 2.3.4.4.A actions were implemented to post a continuous smoke watch in the affected area. The event is reportable as a 24 hour event, as required by 10 CFR 76.120(c)(2)(i); 'An event in which equipment is disabled or fails to function as designed when the equipment is required by a TSR to prevent releases, prevent exposures to radiation and radioactive materials exceeding specified limits, mitigate the consequences of an accident, or restore this facility to a preestablished safe condition after an accident.' The equipment was required by TSR to be available and operable and no redundant equipment was available to perform the required safety function. The Senior NRC Resident Inspector has been notified of this event. The Automatic Data Processing (ADP) computer can be used to interface with the Process Gas Detection (PGD) system part of which is the High Voltage UF6 detection system. The PSS directed that the ADP be bypassed to isolate the fault from the system. The release detection system was tested satisfactorily and returned to service and the smoke watch was secured. |