Final Report
On July 28, 1992, a chemical operator discovered he had received an internal lung exposure to radiation while conducting a routine whole body count at Oak Ridge National Laboratory. The count indicated presence of 0.3 nanocuries of americium-241. Health Physics personnel conducted a follow-up bioassay and verified the internal exposure. The chemical operator was exposed while repacking waste packets in the Alpha Handling Facility Annex on May 6, 1992. Investigators judged the event to be an unusual occurrence in accordance with guidelines in the DOE Radiological Control Manual (June 1992).
On May 5, 1992, a supervisor and two chemical operators, along with a Radiation Protection representative, were working in the Alpha Handling Facility Annex taking inventory and checking waste packets contained in two waste drums. A radiation work permit was not issued for the job because none of the seven criteria established by the Health Physics procedure were strictly met. However, respirators, lab coats, and gloves were required by the Radiation Protection representative. The waste was primarily plutonium-238 and americium-241 and had been in drums for up to two years. New procedures required waste packets to be checked for contamination prior to transfer to the solid waste storage area. The Radiation Protection representative checked all waste packets in both drums and detected no contamination.
The supervisor decided that it would be possible to combine the contents of both drums to reduce the waste volume sent to the storage area. On the morning of May 6, 1992, the supervisor and the chemical operator went into the Annex to transfer the three waste packets from drum 2 to drum 1. The supervisor considered Radiation Protection coverage unnecessary because no contamination was detected the previous evening. Neither the supervisor nor the chemical operator could remember using respirators, and records from Industrial Hygiene did not show a checkout of respirators for this job on that date.
On the afternoon of May 6, 1992, a Radiation Protection representative performing routine checks in the Annex detected contamination on the sole of one shoe when exiting the area. After the shoe was decontaminated the representative returned to the area to find low-level contamination near the drums. The operator who had earlier repacked the waste drum successfully decontaminated the area. Facility personnel performed routine surveys of the Annex before and after the incident and did not detect abnormal levels of contamination.
On August 20, 1992, the chemical operator underwent a recount that confirmed the July 28 count, and a urine sample also tested positive for americium-241. Investigators reported that the recount was delayed because the operator failed to report the first observation to supervision because he received a short-term assignment to the Y-12 plant in early August. Implementation of a new Bioassay Data Management System in late July 1992 was another contributing factor in delaying the recount. Other personnel associated with this work tested negative for internal contamination. According to bioassay data, the Internal Dosimetry Group estimated the operator's intake to be 300 becquerels and his potential dose as follows.
Committed effective dose equivalent 3.6 rem
Annual effective dose equivalent (1992) 0.17 rem
Committed dose equivalent to bone surfaces 65 rem
Annual dose equivalent to bone surfaces (1992) 1.7 rem
Investigators said the evidence suggested that inhalation occurred on the morning of May 6, 1992, as the chemical operator repacked the waste packets into drum 1, which was supported by work records showing the operator handled waste containing americium-241 on that date. The evening of May 5, 1992, was also a possible date, but investigators rejected it based on confirmation that respirators were worn that evening and also on the absence of any contamination then. Somebody re-opened drum 1 on November 19, 1992, and found levels of contamination so high on waste packet 2 that it was not removed for further investigation. Waste packet 2 was initially bagged on August 13, 1990, and contained 0.017 curies of americium-241 in a highly oxidized one-gallon can wrapped in a deteriorating clear plastic bag that had a brown spot about the size of a quarter.
Health Physics personnel surveyed the Alpha Handling Facility Annex in the area of the drums and detected alpha contamination up to 140,000 disintegrations per minute (dpm). The continuous alpha air monitors in the Annex did not alarm during the drum repacking on May 6. Investigators performed a technical assessment and determined that the air monitor was improperly placed to detect releases and its sensitivity was inadequate to warn of airborne concentrations near the derived air concentration limit.
Investigators concluded that the direct cause of the operator's internal exposure was failure to use respiratory protection. They attributed the root cause of the incident to procedures that were inadequate to ensure waste packet integrity until release for storage and appropriate precautions for the radiological risks associated with waste handling outside gloveboxes. Oak Ridge National Laboratory management listed the following lessons learned from this event.
1. Waste procedures should specify adequate protection such as respirators when questionable waste packages are handled. (Personnel modified waste handling procedures to include minimum dress requirements such as respirators, rubber gloves, and laboratory coats; specifications for packing materials that ensure waste packet integrity until final closure; and better documentation of waste handling activities.)
2. Facility records entries should be of sufficient detail to fully describe activities in future documentation.
3. Routine contamination surveys were not adequate to fully characterize overall contamination levels in the facility. Changing locations of smears and probes should be effective in locating previously unknown contamination.
4. Placement of continuous alpha air monitors should be reviewed to ensure that instruments are positioned to be most sensitive to potential airborne releases.
5. Elevated monitoring data or unusual conditions should be reported immediately to facility management.
6. Frisks at exits from areas where airborne contamination is a potential should include a nasal swab from the individual.
Facility management removed the continuous alpha air monitors located in the Alpha Handling Facility Annex, replacing them with portable air samplers until the constant air monitoring is either replaced or the radiological inventory in the Annex no longer requires continuous air monitoring. The potential existed for more severe internal contamination and for impacting more than a single individual. Other DOE facilities that handle similar types of radiological material may wish to consider the corrective actions from this incident to help prevent similar occurrences at their facilities.