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This is a 30-day notification to inform the NRC of missing licensed material in accordance with 10 CFR 20.2201 (a)(l)(ii). On June 24, 2010, while conducting the quarterly inventory of radioactive sources in accordance with Humboldt Bay Power Plant (HBPP) Unit 3 Radiation Control Procedure RCP-6D, 'INVENTORY AND CONTROLS FOR RADIOACTIVE SOURCES,' it was discovered that source number 498 was missing from the count room. This source is for the calibration of gamma detectors, but had not been used for that purpose this year. The source is a filter, mixed gamma source with an activity of 1.025 microCi as of July 1, 2008. The radionuclide mix of the source is as follows:

                                      Gammas/second            Activity (Ci)           10 CPR 20 Appendix C (Ci)

Am-241 7.02e+02 5.20e-08 1.00e-09 Cd-109 9.80e+02 7.12e-07 1.00e-06 Co-57 5.10e+02 1.61e-08 1.00e-04 Ce-139 7.10e+02 2.39e-08 1.00e-04 Hg-203 1.61e+03 5.63e-08 1.00e-04 Sn-113 1.01e+03 4.19e-08 1.00e-04 Cs-137 6.29e+02 2.00e-08 1.00e-05 Y-88 2.42e+03 6.99e-08 1.00e-05 Co-60 1.18e+03 3.18e-08 1.00e-06 The above radionuclide composition yields an aggregate quantity of missing licensed material of 53 times the quantity specified in 10 CFR 20 Appendix C, which exceeds which exceeds the 30-day reporting criterion of 10 times the quantity specified in Appendix C. An extensive search has not been successful in locating the source to date, and thus PG&E is making this 30-day notification in accordance with the requirements of 10 CFR 20.2201(a)(1)(ii). PG&E is continuing to investigate the cause of this event using the Technical Review Group (TRG) process and will provide a written report within 30-days in accordance with the requirements of 10 CFR 20.2201(b)(1)(a). This material was last accounted for on 4/8/10. The licensee informed NRC Region IV staff. THIS MATERIAL EVENT CONTAINS A "LESS THAN CAT 3" LEVEL OF RADIOACTIVE MATERIAL Sources that are "Less than IAEA Category 3 sources," are either sources that are very unlikely to cause permanent injury to individuals or contain a very small amount of radioactive material that would not cause any permanent injury. Some of these sources, such as moisture density gauges or thickness gauges that are Category 4, the amount of unshielded radioactive material, if not safely managed or securely protected, could possibly - although it is unlikely - temporarily injure someone who handled it or were otherwise in contact with it, or who were close to it for a period of many weeks. For additional information go to http://www-pub.iaea.org/MTCD/publications/PDF/Pub1227_web.pdf This source is not amongst those sources or devices identified by the IAEA Code of Conduct for the Safety & Security of Radioactive Sources to be of concern from a radiological standpoint. Therefore is it being categorized as a less than Category 3 source