05000461/LER-2004-006
| I | |
| Event date: | 10-07-2004 |
|---|---|
| Report date: | 11-03-2004 |
| 4612004006R00 - NRC Website | |
PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
Unit: 1 Event Date: 10/7/2004� Event Time: 1430 Central Daylight Time Mode: 1 (POWER OPERATION)� Reactor Power: 95 percent
DESCRIPTION OF EVENT
In 1991, four unirradiated nuclear instruments (Nis), including detectors [DET], cables [CBL], and connectors [CON] were identified as being damaged due to bent connector ends resulting in bad detector signals. The disposition for the four Nis was to cut the detectors from the cables and place the detectors in a small Special Nuclear Material (SNM) container. Tamper seals were applied to the container. The remaining cables and connectors were to be disposed of as trash.
On October 7, 2004, the plant was in Mode 1 with reactor power at 95 percent. The small container of SNM had been moved from its normal storage location to another plant location in preparation for disposal. Reactor Engineers opened the container to verify the contents and discovered that the container had only one of the expected four detectors and three unexpected signal cable connectors; thus three unirradiated nuclear instrument detectors containing SNM were unaccounted for. Condition report 261339 was initiated to address this issue.
The contents of the SNM container were periodically inventoried since 1991 by verifying that the tamper seals were intact in accordance with the site SNM inventory procedure. In July 2004, a periodic SNM inventory was performed in accordance with the Exelon SNM inventory procedure; however, as allowed by the Exelon SNM inventory procedure, the contents of the small SNM container were not inspected since the tamper seals were intact.
A search of storage facilities including other containers of SNM was conducted for the missing detectors; the detectors were not found. The other containers in the storage area were opened and a serial number inventory was performed to account for NI detectors. A search of station records was conducted for records of the disposition of the detectors; no other records of disposition were found. The station concludes that the detectors were mistakenly disposed of as uncontaminated connectors in the station trash that was subsequently buried in a local landfill. A search of landfills was not performed due to the elapsed time of 13 years since disposal of the material, and based on the extremely small amount of SNM that poses no danger to the public and the difficulty of detecting such very low activity material.
The total mass of U235 in the unaccounted for SNM was less than one gram. The actual total mass was determined to be approximately 6 milligrams. The actual U235 activity was 0.012 micro-curies, exceeding 10 times the Part 20 Appendix C activity (0.010 micro-curies). Therefore, this loss of SNM is reportable under the provisions of 10CFR20.2201(a)(1)(ii). The 30-day telephone report required by 10CFR20.2201(a)(1)(ii) was completed via Emergency Notification System Event Number 41130 at 1635 hours0.0189 days <br />0.454 hours <br />0.0027 weeks <br />6.221175e-4 months <br /> (Central Daylight Time) on October 18, 2004. This 30-day written report is being submitted in accordance with the provisions of 10CFR20.2201(b).
CAUSE OF EVENT
This event occurred in 1991. The apparent cause of this event is attributed to human error associated with the NI connectors being cut and placed in the SNM container rather than the detectors.
SAFETY ANALYSIS
The detectors contain an extremely small amount of SNM and pose no danger to the public.
The U235 mass in the unaccounted for SNM was less than one gram (actual mass approximately 6 milligrams). An evaluation of this event concluded that the dose to a member of the public for one calendar year is 0.019 millirem (at 30 centimeters).
CORRECTIVE ACTION
An accounting of the other NI detectors in the storage area was completed by opening containers and performing a serial number inventory of container contents.
The future practice for disposing of defective unirradiated NI detectors will be to leave the detector, cable and connector intact as a unit, cutting will not be allowed. (CA 261339-04)
PREVIOUS OCCURRENCES
None
COMPONENT FAILURE DATA
None FOLLOWING INFORMATION IS REQUIRED BY 10CFR20.2201(b)
DESCRIPTION OF LICENSED MATERIAL INVOLVED, INCLUDING KIND, QUANTITY, AND
CHEMICAL AND PHYSICAL FORM
Three Nuclear Instrument detectors (Boiling Water Reactor) — two Source Range Monitor detectors and one Intermediate Range Monitor detector.
Special Nuclear Material (SNM) U-235 and U-238 encapsulated in stainless steel.
Detectors are approximately 2.5 inches long and about 0.25-inch diameter.
Total amount of U-235: 0.00615 gram Total amount of U-238: 0.00046 gram Total activity of U-235: 0.012 micro curie Total activity of U-238: 0.001 micro curie Total amount of Solid Uranium Dioxide: 0.00753 gram
DESCRIPTION OF THE CIRCUMSTANCES UNDER WHICH THE LOSS OR THEFT OCCURRED
See Description of Event section of this report A STATEMENT OF DISPOSITION, OR PROBABLE DISPOSITION, OF THE LICENSED
MATERIAL INVOLVED
The three detectors were probably buried in a local landfill 13 years ago.
EXPOSURES OF INDIVIDUALS TO RADIATION, CIRCUMSTANCES UNDER WHICH THE
EXPOSURES OCCURRED, AND THE POSSIBLE TOTAL EFFECTIVE DOSE EQUIVALENT TO
PERSONS IN UNRESTRICTED AREAS
There is no known exposure to individuals. Radiological Technical Evaluation RTE 2004-25 ED concluded that the dose to a member of the public for one calendar year is 0.019 millirem (at 30 centimeters).
ACTIONS THAT HAVE BEEN TAKEN, OR WILL BE TAKEN, TO RECOVER THE MATERIAL
See Description of Event section of this report
PROCEDURES OR MEASURES THAT HAVE BEEN, OR WILL BE, ADOPTED TO ENSURE
AGAINST A RECURRENCE OF THE LOSS OR THEFT OF LICENSED MATERIAL
See Corrective Action section of this report