Airborne Thorium From Welding Rods
See the memorandum from L. J. Cunningham to J. H. Joyner (and others) dated June 18, 1993. This memo addresses a question from a corporate health physicist at a nuclear utility that had found airborne thorium in a nuclear power plant. Although this regulatory position is presented quite clearly in 10 CFR Part 40, it is being issued as a health physics position to call attention to an exemption that might otherwise be overlooked by Part 50 licensees.
A response was requested as to whether there are any NRC regulatory requirements that apply to airborne thorium caused by grinding the tips and using welding rods containing thorium. The response stated that 10 CFR 40, "Domestic Licensing of Source Material", in subsection 40.13 (c) (1) (iii), provides that any person is exempt from the regulations in Part 40 and from requirements for an NRC license to the extent that the person receives, possesses, uses, or transfers any quantities of thorium contained in welding rods. Therefore, there are no NRC regulatory requirements that apply to airborne thorium caused by grinding and using welding rods that contain thorium.
Additional technical information concerning the considerations for the 10 CFR Part 40 exemption for thoriated welding rods does not include any information on the radiological hazards associated with their use.
However, some information on the radiation doses associated with the use of these rods can be found in the following references:
NUREG / CR-1039, "Estimated Radiation Doses from Thorium and Daughters Contained in Thoriated Welding Electrodes," December 1979.
NUREG / CR-1775, "Environmental Assessment of Consumer Products Containing Radioactive Material," October 1980.
NCRP Report No. 95, "Radiation Exposure of the U.S. Population from Consumer Products and Miscellaneous Sources," 1987.
E. M. Crim and T. D. Bradley, Abstracts of Papers Presented at the Thirty-Eighth Meeting of the Health Physics Society, Atlanta, Georgia, 11-15 July, 1993, Health Physics, Vol. 64, Supplement 1, p. S85, June 1993.
Reference 2 includes the following summary statement concerning radiation doses:
The maximum individual fifty-year dose commitment to bone for welders was estimated at between 55 mrem and 2 rem for a one-year exposure. Welders not engaged in welding at home and occasional welders were estimated to receive a bone dose commitment of 16 to 575 mrem and 1.3 to 115 mrem, respectively. A maximum individual bone dose commitment range between 30 and 230 mrem was estimated for nonwelders. External doses for all group members were estimated to be less than 1 mrem.
Reference 4 includes the following statement concerning airborne thorium (Th-232) from welding rods:
The results for the grinding and welding operations to date, show that all personal and area air samples are below the maximum permissible concentration for Th-232 as well as below the derived air concentration.
Regulatory references: 10 CFR 40.13
Subject codes: 7.2, 8.4