A Review of Criticality Accidents A Review of Criticality Accidents

• Senior management should be aware of the hazard
of accidental criticality and its consequences.
Difficult cost-risk-benefit decisions must be made
by upper management. There will always be issues
of production quotas and timetables, which management
must balance against acceptable levels of
risk acceptance. Most of the accidents occurred
during the peak years of the Cold War, when high
production levels were perceived to be of utmost
importance. Nevertheless, senior management apparently
learned from these accidents and allocated
resources for criticality control. The three major
expenditures were for criticality specialists dedicated
to the support of process operations, favorable
geometry and poisoned vessels, in spite of their cost
and production drawbacks, and the generation of
additional critical mass data. It should be noted that
before the first criticality accident in the R.F.,
nearly all process vessels were of unfavorable geometry
in order to maximize production; by 1968
more than 95% of them had been replaced with
favorable geometry vessels.
• Regulations should exist which promote safe and
efficient operations. Those who worked in the
critical experiment facilities were directly aware of
the risks associated with criticality accidents. Some
of these people also recognized the need for formal
safety guidance to be made available to those who
operated process facilities. Accordingly, they, together
with process experts, spontaneously set out
to develop and document criticality safety guidance
for process operations. In the U.S., technical guidance
and administrative good practices were codified
in a series of documents entitled Nuclear Safety
Guide, beginning with the 1957 edition. 36 Many of
these same people then became involved in the
development of American national standards and
then international standards. Similar actions developed
in parallel in other countries, both those that
had experienced criticality accidents and those that
had managed to work with fissile materials without
accidents. The marked decrease in the accident rate
by the late 1960s was probably due to a combina-
tion of adherence to these newly codified regulations
and guidance and upper management attention
to this new hazard.
• Regulators, like process supervisors, should
ensure that those they regulate are knowledgeable
and capable. While the responsibility for
accident prevention must rest first and foremost
with those directly in charge of the work, regulatory
authorities have a distinct role to play. Similar to the
process supervisor, the regulator should also ask
questions such as: “When was the last time that I
saw the job being performed properly?” and
“When was the last time I talked to the process
supervisors and became assured that they understood
the operations under their control and exhibited
a safety conscious behavior and attitude?” At
the time of the Wood River Junction accident,
131 days after plant startup, there still had not been
a visit by the regulatory authorities. At the time of
the 1997 accident, regulatory authorities were not
aware of changed criticality limits of the operation
even though the change had been made 13 years
before.
Conclusions
Criticality accident risks will not vanish as long as
significant quantities of fissile materials exist. However,
sufficient knowledge has been gained from
planned experiments and from accidents to provide a
high degree of confidence that, with appropriate
support from senior management, reasonable diligence
on the part of criticality staff and operating personnel,
and continued adherence to codified fundamental
safety principles and guidance, accident likelihoods
can be maintained at the current low level or possibly
be reduced even further. This will require continued
education of future personnel at all levels—regulatory,
upper management, supervisory, criticality staff, and
operations—on the lessons of the past so that similar
accidents will not be repeated.
The following statement, while woven throughout
the preceding text is considered worthy of being
repeated: All accidents have been dominated by
design, managerial, and operational failures. The
focus for accident prevention should be on these
issues.
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