A Review of Criticality Accidents A Review of Criticality Accidents

Monitoring could take the form of visual inspections,
physical cleanings, radiation emission measurements,
etc. Criticality control and fissile material
accountability are important issues and often
mutually supportive.
• Operations personnel should know how to respond
to foreseeable equipment malfunctions or
their own errors. Hasty and inappropriate responses
to process malfunctions have led to more
than one accident. This underscores several issues:
first, the need for operator understanding of the
concept of criticality and of the importance of the
particular criticality controls for the process at
hand; second, the importance of care and thoroughness
in determining credible abnormal conditions
for analysis; and third, the importance of having
considered responses to unplanned conditions.
• Operations personnel should be trained in the
importance of not taking unapproved actions
after an initial evacuation. Reentry, except perhaps
in lifesaving situations, should be undertaken
only after the accident evolution has been technically
evaluated, thoroughly understood, and
planned actions have been approved. During one
accident, unapproved reentry into the accident site
and without adequate understanding of the criticality
hazard, followed by impulsive actions, led to a
loss of life. In a second accident, significant exposures
occurred from an ineffective and ill considered
reentry and only chance prevented a fatality.
• Readouts of radiation levels in areas where accidents
may occur should be considered. Knowledge
of radiation levels in evacuated areas has
proved valuable in planning recovery actions. Many
of the accidents involved power histories that extended
from minutes to many hours. In two cases,
the accident termination process involved hands on
intervention at times of expected minimal exposures.
The successes of these interventions were
based on detailed knowledge and understanding of
the excursion history and its expected behavior.
• Operations involving both organic and aqueous
solutions require extra diligence in understanding
possible upset conditions if mixing of the
phases is credible. Obscure process conditions and
unplanned chemistry have led to at least four accidents.
• Operations personnel should be made aware of
criticality hazards and be empowered to implement
a stop work policy. This awareness should
come from a mix of formal and informal training.
These include classroom, on–the–job from immediate
supervision, and discussions with criticality
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staff. Lack of understanding of criticality hazards
has contributed to several accidents and to exacerbated
consequences.
• Operating personnel should be trained to understand
the basis for and to adhere to the requirement
for always following procedures. Lack of
adherence to available procedures, either inadvertently
or knowingly, has been a major contributor to
several accidents.
• Hardware that is important to criticality control
but whose failure or malfunction would not necessarily
be apparent to operations personnel,
should be used with caution. Operational oversights
such as failure to actuate valves per requirements
have led to accidents. Duplicate hardware
controls, strict procedural controls with multiple
checks on operator actions, and diligent maintenance
may be appropriate.
• Criticality alarms and adherence to emergency
procedures have saved lives and reduced exposures.
Most of the 22 accidents involved excursions
that were not terminated after a single burst. Prompt
detection and immediate evacuation of personnel
within several meters of the accident have been
significant in saving lives and limiting exposures.
Lessons of Supervisory, Managerial, and
Regulatory Importance
• Process supervisors should ensure that the operators
under their supervision are knowledgeable
and capable. Several accidents could have
been avoided or the consequences lessened had
supervisors been more aware of the routine actions
of operators in performing their tasks. It is one
thing to have written procedures that are intended to
be followed in order to provide for safe operations.
It is another that these procedures are understood
and being followed as intended. Supervisors might
ask themselves periodically, “When was the last
time I saw the job being performed properly?”
• Equipment should be designed and configured
with ease of operation as a key goal. More than
one accident, including the accident in Japan might
have been avoided if operators had been provided
user-friendly equipment.
• Policies and regulations should encourage self–
reporting of process upsets and to err on the side
of learning more, not punishing more. At least
one accident and attendant fatality were caused by a
supervisor’s excessive concern for bringing a process
back within required limits before it was discovered
by management. Improvised operations
were performed without accompanying awareness
of the criticality hazards.