On January 13, 2011, the licensee received a dosimetry report which stated that one of their employees received a year-to-date exposure of 55 mSv (5.5 rem) which was above the statutory limit of 50 mSv (5 rem). The overexposure was received in December 2010 during the emergency repair of a cyclotron unit over a period of several days. However, the affected employee’s real-time dosimeter indicated a much lesser exposure, calling into question the measurement indicated on the permanent dosimeter. Massachusetts subsequently performed an onsite inspection in February 2011 and determined that the affected employee did receive an exposure of 55 mSv (5.5 rem). The licensee attributes the overexposure to misinterpretation of existing policy which restricts workers when year-to-date exposures approach limits and over-reliance on real-time dosimeters. The licensee implemented several corrective actions to include application of administrative correction factors to readings of job-specific dosimeters to obtain more conservative real time results; modifying the permanent dosimeter exchange frequency to obtain more current year-to-date exposure totals; and revision to existing policy. The affected employee had been temporarily removed from potentially high exposure operations during the licensee’s investigation, and was re-instated on March 3, 2011.

Massachusetts General Hospital, Boston MA
Event date: 
Thu, 2011-01-13
Event sender: 
Huffman William (Bill) NRC Headquarters Operation Officer