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Information Notice No. 83-73: Radiation Exposure from Gloves Contaminated with Uranium Daughter Products
SSINS NO. 6835 IN 83-73 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 OCTOBER 31, 1983 Information Notice No. 83-73: RADIATION EXPOSURE FROM GLOVES CONTAMINATED WITH URANIUM DAUGHTER PRODUCTS Addressees: All licensees authorized to process uranium as source material and metal producers of alloys containing uranium as source material except uranium mills, UF-6 facilities, uranium fuel fabrication plants, and nuclear power plants. Purpose: The purpose of this Notice is to bring to the attention of all persons involved in the administration and operation of uranium processing facilities a recent incident that resulted in multiple exposures to workers' hands in excess of regulatory limits, and to discuss its generic implications for other, similar operations. Description of Incident: Nuclear Metals, Inc., Concord, Massachusetts, receives depleted uranium derbies that are sent to their foundry for melting, alloying, and casting. The melting is done in graphite crucibles in a vacuum furnace. Foundry workers load the crucibles into the furnace and, once a liquid state is reached, the metal is poured into castings from the bottom of the crucible. The foundry workers, wearing leather gloves, remove the brick top from the furnace, remove the crucible from the furnace, and subsequently clean the crucible before it is reused. One of the licensee's health physics technicians found that the leather gloves worn by the foundry workers were routinely contaminated during handling of the bricks and crucible upon completion of a melt. Measurements made with a Junotype survey meter, with the gloves turned inside out, showed radiation levels inside the gloves between 270 and 1000 millirems per hour. While foundry workers had been provided with wrist badges, these wrist badges did not adequately measure the exposure to workers' hands. The badges were located too far from the hands that were receiving most of the radiation exposure. Subsequently, dosimeters were placed on the fingers of foundry workers. Four workers were removed from work because their measured exposure exceeded the licensee's administrative limit of 12.5 rems per quarter for the first quarter of 1983. An investigation was conducted to determine the workers' hand exposures during the fourth quarter of 1982 and the first quarter of 1983. It was estimated from TLD measurements and interviews with foundry workers that beta . IN 83-73 October 31, 1983 Page 2 of 2 radiation dose rates of about 1 rem per hour existed inside the contaminated gloves. Based on those estimated dose rates, from 10 to 15 foundry workers received hand exposures of up to 125 rems per.quarter during both quarters. Similar doses may have been received in previous quarters. The licensee's investigation is continuing. Discussion: The beta radiation dose rate at the surface of uranium metal is typically 230 millirems per hour or less. However, when uranium is melted, less dense daughter products of uranium-238, primarily thorium-234 and protactinium-234m, float to the surface of the molten metal. When the uranium is poured, significant quantities of these daughter products remain behind, coating the crucible, fire brick, and inside of the furnace. The beta radiation dose rate from these residual daughter products is much higher than that of the original uranium. In addition, these daughter products are loose or transferable. Exposure to these daughter products, or transfer to clothing, tools, or other items is likely to result in unanticipated beta radiation doses. Protactinium-234m emits a beta particle with a maximum energy of 2.28 MeV, that contributes to the majority of the beta dose from the uranium-238 daughter products remaining in the crucible and found on contaminated clothing or equipment. All uranium manufacturing and processing licensees that melt uranium should review their operations to ensure that workers are not receiving excessive radiation exposures from unsuspected high levels of beta contamination on protective clothing or equipment. It should be kept in mind that available ring or finger dosimetry may not adequately assess the whole-body exposure from beta radiation fields. To assess whole-body radiation doses from fields of radiation, whole-body dosimeters should be worn. No written response to this Information Notice is necessary. If you need additional information regarding this matter, contact the Administrator of the appropriate NRC regional office or this office. James G. Partlow, Acting Director Division of Quality Assurance, Safeguards, and Inspection Programs Office of Inspection and Enforcement Technical Contact: J. R. Metzger, IE (301) 492-4947 Attachment: List of Recently Issued Information Notices .
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