On February 23, 1995, a radiological controls technician (RCT) at the Los Alamos National Laboratory (LANL) discovered that the radiological posting for a building at the TA-39 facility was incorrect when he measured 20 millirem/hour at the door. Four days later, while investigating the condition, the RCT surveyed a shipping container containing a neutron source and measured a radiation dose rate of 230 millirem/hour at a distance of 30 centimeters. Facility personnel determined that there was no adverse impact on the health or safety of personnel and no danger to the environment. However, there was the potential for radiation overexposure to personnel working in the vicinity of the container. (ORPS Report ALO-LA-LANL- FIRNGHELAB-1995-0006)
In January 1994, the source custodian for the Shock Wave Physics project transferred two plutonium-beryllium neutron sources from their storage containers into individual Department of Transportation (DOT) shipping containers. He performed this task after consulting with an RCT assigned to the area. The neutron source storage containers have hydrogenous shielding, the best shielding for neutrons. The DOT shipping containers do not have neutron shielding. The difference in neutron shielding between the two types of containers resulted in an increase in the surrounding radiation levels when the neutron sources were moved from the storage containers to the shipping containers.
An RCT was not present to monitor the radiation levels when the sources were moved to the shipping containers. Consequently, the radiological posting was not updated to indicate that the building was now a high radiation area.
On the morning of February 27, after measuring the 230 millirem/hour reading from one of the shipping containers, the RCT posted the building as a high radiation area at the door and designated an area outside of the building as a radiation area. The neutron sources remain stored in the DOT shipping containers.
Facility personnel are continuing the investigation to determine the causes, to define corrective actions, and to develop lessons to be learned.
This event illustrates the importance of ensuring that changes in the amount of radiation shielding are analyzed before moving radioactive material between storage and shipping containers. This is needed for two reasons: (1) to prevent unanticipated increases in local radiation levels where personnel are working and (2) to ensure that the proper radiological posting and controls are implemented. Had personnel been working near or handling the shipping containers, they may have received an unexpected external radiation exposure.
Personnel at DOE facilities may wish to review chapter 3 of DOE/EH-0256T, Radiological Control Manual, which provides requirements for planning radiological work, and Appendix 3A which provides a checklist of items to consider to reduce potential radiation exposure.