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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 41130 | 18 October 2004 19:30:00 | 10 CFR 20.2201(a)(1)(ii) | Unaccounted for Special Nuclear Material | In 1991, four unirradiated nuclear instrumentation (NI) detectors (includes detector, cable, and connector) were identified as being damaged. These four NI detectors were dispositioned by cutting the detectors from the cable and placing these detectors in a small Special Nuclear Material (SNM) container which then had tamper seals applied. The remaining cables and connectors were disposed of as trash. On October 6, 2004, the small SNM container was moved from its normal storage location to another plant location in preparation for disposal and was opened to verify the contents on October 7, 2004. The actual contents of the container were three NI connectors (not detectors) and one NI detector. Therefore, three NI detectors containing SNM were identified as unaccounted for. The contents of this SNM container have been periodically inventoried since 1991 verifying that the tamper seals are intact in accordance with the site SNM inventory procedure, and in March 2004, a periodic SNM inventory was performed in accordance with Exelon SNM inventory procedure. As allowed by the Exelon SNM inventory procedure, however, the contents of the small SNM container were not inspected since the tamper seals were intact. A search of the normal NI detector storage location was performed and it was verified that the unaccounted for detectors were not in another container. The other NI detectors in the storage area were accounted for by performing a serial number inventory. Only the three NI detectors missing from the small SNM container are unaccounted for. The total mass of U235 in the unaccounted for SNM was much less than one gram. The actual total mass was determined to be approximately 6 milligrams. It has been determined that the U235 activity of the unaccounted for SNM was greater than 10 times the activity listed in 10CFR20, Appendix C. The actual U235 activity was determined to be 0.012 microcuries, which exceeds 10 times the Part 20 Appendix C activity (i.e., 0.010 microcuries). Therefore, this loss of SNM is reportable in accordance with the requirements of 10 CFR 20.2201(a)(1)(ii). Both the NRC Resident and IEMA Resident were notified. CPS records are being reviewed to determine the actual disposition of the NI cables that were disposed of in 1991. |