Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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
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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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