Contaminated Rebar from Juarez
Sometime in November, 1983, Sotelo and Ricardo
Hernandez removed a Picker C-3000 teletherapy unit from a hospital
At the scrapyard, many of the cobalt pellets that had
remained in the source capsule were scattered around when the teletherapy
unit was dropped by a magnetic crane. The rest of the pellets stuck to the
magnet and became mixed with steel leaving the scrapyard. Most of the
latter went to two local foundries. One foundry melted down the steel to
produce the pedestal-style table legs used in fast food restaurants. The
other produced steel rods (re-bar) for reinforcing concrete.
The problem was discovered when a truck carrying the
reinforcing rods made a wrong turn at
Estimates place the radiation exposure of at least 4 people in the range of several hundred rad. Two workers at the contaminated scrapyard became sterile, possibly permanently. No one died. The major concern is increased risk of cancer among the exposed individuals.
The following information is taken from the NRC Inspection Manual, Manual Chapter 1302 Action Levels for Radiation Exposures and Contamination Associated with Materials Events Involving Members of the Public:
"On January 17, 1984, Region IV was informed that Los Alamos National Laboratory (LANL) had detected some radioactive reinforcing bars (rebar) in a shipment mistakenly delivered to LANL. The rebar was determined to have been inadvertently contaminated with cobalt-60 (Co-60) and that the shipment had come from a supplier in Mexico through a broker in Phoenix, Arizona.
Guidance on dose levels for members of the public who might occupy structures containing the contaminated rebar was established by the Office of Nuclear Material Safety and Safeguards (NMSS). Because the exposure to Co-60 was considered similar to Ra-226, the guidance in 40 CFR Part 192 was selected as a basis for remedial action. Remedial action, for gamma radiation in buildings, is addressed in 40 CFR 192.12 (b)(2). This section, in part, requires that the: "level of gamma radiation shall not exceed the background level by more than 20 microroentgens per hour." Using this as a reference point and an occupancy factor of 0.75, the total exposure is within 1.3 mGy/yr (130 mrad/yr). The NRC guidance also noted that the 1.3 mGy/yr (130 mrad/yr) level: "should, in most circumstances, maintain doses within 5 mSv/yr (500 mrem/yr) from all sources of radiation as recommended by the ICRP and, considering the 5.3 year half-life of Co-60 contamination, will not likely cause the average annual lifetime dose to exceed 1 mGy (100 mrad)."
Related Notes. Because of the implementation of the revised 10 CFR Part 20 (effective January 1, 1994), however, the NMSS recommended guidance for situations of this type in the future is to limit exposures to within 1 mSv (100 mrem) per year."
Donated by the Arizona Radiation Regulatory Agency courtesy of Paul Harvey
Copyright 1999, Oak Ridge Associated Universities