It was reported to Radiological Health Branch (
RHB), Granada Hills that a
Texas licensee, Gamma Surveys, a Division of Global Process Diagnostics, Inc. ( Gamma Surveys) , was conducting density level measurements using sealed sources under reciprocity at the Conoco Phillips Corporation refinery in Carson, CA, the evening of 12/21/04. Special form sealed sources containing radioactive material are employed for "gamma scanning," diagnostic evaluation, typically density or level measurements, of industrial processes or equipment. At about 1900 one such source, 287 mCi,
Co-60, contained in a collimating device at the end of a stainless-steel, stranded cable, was being lowered down the outside of a large, cylindrical "distillation vessel, " designated FR-1 Flasher Column, 200 ft. high and 28 ft. in diameter. Stiffening rings which protrude about 18 inches externally encircle the vessel at various heights. As the source is being lowered down the side of the vessel, the operator located at the top of the vessel must manually "shake" the cable to get the source over the protruding stiffening rings. On this occasion, the collimating device with the
Co-60 source broke at the cable during this shaking to get it over a stiffening ring 20 feet from the top. The source came to rest on the stiffening ring, in the " unshielded" condition, where it remained overnight. However, Gamma Surveys indicated that the area was cleared of personnel and cordoned off. Radiation surveys were taken at the ground level showing no appreciable dose rates, approximately 0.04 mR/hr.
The next day, 12/22/04, Gamma Surveys proposed a recovery plan to lower an operator in a man-basket down to the source to manually put the source back in its shielded condition ( normal practice) and then attach a replacement cable to the collimating device so that it may be reeled back into its shielded container at the top of the vessel for subsequent evaluation and repair of the damaged system. After consultation with RHB staff and the RSO for Gamma Surveys, this plan was effected. By about 5 PM, 12/22/04, the source recovery was completed without problems.
An investigation has been initiated to follow-up.