 INES 2 |
Potential Overexposure to Members of the Public |
On July 12, 2004, the Texas Department of Health, Bureau of Radiation Control (the State) notified Nuclear Regulatory Commission (NRC) of a potential exposure to members of the general public from an unshielded cesium-137 (Cs-137) collimated sealed source. The Cs-137 source was used for well logging operations in Pecos County, Texas, and contained 63 gigabecquerel (1.7 curie) of radioactivity. This is a Category 3 source (IAEA-TECDOC-1344, Categorization of Radioactive Sources, July 2003)
The Texas licensee notified the State on July 12, 2004, of the missing sealed source from a well logging tool. The licensee reported that a well logging crew was using a rig without a floor at a well site in Pecos County, Texas. During the evening of July 9, 2004, the crew moved to a new site. While setting up for work at the new site, the crew realized that the source was missing from the well logging tool.
The crew returned to the original site and found the source in mud approximately 10-15 feet from the previous rig location. It was suspected that the source was missing for 24-36 hours. Licensee management was dispatched on July 13 to assess potential doses to the crew and members of the public and to investigate the event. The State also dispatched an inspector to the site.
On July 15, the State provided an update of the investigation, and reported that a person on the drilling crew (defined by the U.S. regulations as a member of the public) may have picked up the source by hand. An initial analysis resulted in a dose estimate of 0.6 gray (60 rad) to the individual's hand. The regulatory limit for an individual member of the public is 1 mSv (0.1 rem). Additional analyses continue in order to determine whether any other members of the public were exposed. The licensee is sending members of the well logging crew to a local hospital for blood work. The investigation has determined that no radiation surveys were performed, and written operating procedures had not been followed by the logging crew. The licensee and the State are still investigating the event, and the State will keep NRC informed of its findings.
Event date: Fri, 09-07-2004
