United States Nuclear Regulatory Commission - Protecting People and the Environment

Loss of Control of Cesium-137 Well Logging Source Resulting in Radiation Exposures to Members of the Public (NUREG-1794)

On this page:

Download complete document

Publication Information

Manuscript Completed: April 2004
Date Published: October 2004

Prepared by:
D. Boal, R. Brown, R. Leonardi,
M. Shaffer, S. Sherbini

U.S. Nuclear Regulatory Commission
Region IV
611 Ryan Plaza Drive
Arlington, TX 76011-4005

Availability Notice


This report describes the events that occurred on a drill rig in Montana on May 21, 2002, that led to the unplanned radiation exposure of 31 rig workers. These workers were not radiation workers, and were therefore considered by the Nuclear Regulatory Commission to be subject to the Agency's dose limit for members of the public, which is 0.1 centisitevert (cSv) (0.1 rem) per year. The doses assessed by the Nuclear Regulatory Commission to have been received by the workers as a result of this incident were, for most of the exposed workers, above the dose limit for members of the public, but in all cases was far below the dose limit for radiation workers of 5 cSv (5 rem) per year. Although the doses received are relatively low and are not expected to cause any clinical effects, they are in violation of the Nuclear Regulatory Commission's regulations.

Included in the report is a detailed description of the sequence of events, the root and other causes for the event, a detailed description of the methods used to assess the worker's doses, and a discussion of the biological dosimetry undertaken for some of the exposed workers to support and verify the dose assessments. A discussion of the less than adequate state of biological dosimetry in the United States is also included.

Page Last Reviewed/Updated Thursday, January 02, 2020