A Review of Criticality Accidents A Review of Criticality Accidents

than implied by the figure. At the time of the accident,
processing of six of the ingots had been completed, and
only ingot 3 needed to remain in 1391-B. According to
the shift instructions, Operator A was to
1. transfer the six processed ingots to glovebox 6, and to
2. transfer four ingots from glovebox 6 and two from
glovebox 12 to glovebox 13 for processing.
The intended order of ingot transfers, as specified in
the shift instructions, is illustrated in Figure 30. The
actual order of ingot transfer is shown in Figure 31,
Frames 1 through 6. Operator A transferred two ingots,
6 and 7, from workstation 1392 to glovebox 6. These
ingots were replaced in workstation 1392 by two ingots,
8 and 9, from glovebox 6. Both of these actions were in
accordance with the shift instructions.
Motivated by production pressures to conduct the
ingot transfers as soon as practical, Operator A (without
authorization and in violation of procedures) requested
Operator B to assist him. Operator A then instructed
Operator B to transfer ingots 1 and 2 to glovebox 6 and
to reload their containers with ingots 10 and 11 from
glovebox 12. However, Operator B, who was not
working from written instructions, instead transferred
ingot 3 into the container already holding ingot 4,
violating the container administrative limit. Operator B
then transferred ingot 10 from glovebox 12 to the
container that previously held ingot 3 within 1391-B.
Operator A, who had left the area to perform other
tasks, then returned and resumed the work as per the
shift instructions, assuming, but not confirming, that
Operator B had performed the tasks requested.
Operator A then transferred ingots 1 and 2, believing
them to be ingots 10 and 11, into the same container
already holding ingots 3 and 4 (data on the individual
ingots as to size and mass are not well known). The
48
actions of Operator A, even if the container in 1392 had
been empty, were also a direct violation of the container
administrative limit. Frames 5 and 6 of Figure 32 show
these transfers.
While placing the fourth ingot, 1 (mass less than
2 kg), into the container, Operator A experienced an
instantaneous and significant rise in the temperature near
his hands and arms and saw a flash of light. The
excursion was immediately terminated due to thermal
expansion and the removal or ejection of ingot 1. The
total mass of the four ingots was 10.68 kg. At the same
instant, the criticality alarm sounded in two buildings,
901 and 925, causing all personnel to evacuate. The
alarm system detectors were G-M tubes with activation
thresholds of 110 mR/h.
After the alarm systems had sounded, Operator A
removed two of the three remaining ingots from the
container, moving one into workstation 1391-A, and the
other into 1391-B. During the investigation, the operator
could not clearly recall if he had instinctively removed
his hand while still holding the fourth ingot or if it had
been forcefully ejected as the result of a sudden thermal
expansion brought on by the rapid energy release.
Plutonium samples were taken from each of the four
ingots and analyzed for 140 La content using gamma–ray
spectrometry. From this the number of fissions in this
single excursion was estimated to be 3 × 10 15 .
Operator A received an estimated total body dose of
250 rad, and more than 2,000 rad to his arms and hands,
necessitating amputation up to the elbows. Later his
eyesight also became impaired. Seven other people
located at various distances from glovebox 13 received
doses between 5 and 60 rad, with the predominant
contribution being from fast neutrons. The equipment
was not damaged and no contamination resulted.
To Glovebox 6 To Glovebox 6
From Glovebox 6 From Glovebox 12
Figure 30. Intended sequence for the transfer of ingots from and to Glovebox 13.