Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR MATERIALS SAFETY AND SAFEGUARDS
WASHINGTON, D.C. 20555
March 5, 1991
Information Notice No. 91-14: RECENT SAFETY-RELATED INCIDENTS AT
LARGE IRRADIATORS
Addressees:
All Nuclear Regulatory Commission (NRC) licensees authorized to possess and
use sealed sources at large irradiators.
Background:
This issue was previously addressed in Information Notice No. 89-82,
"Recent Safety-Related Incidents at Large Irradiators" (attached). Because
of the significance and frequency of recurrence of these incidents, NRC
believes this issue should be reiterated.
Purpose:
This information notice is intended to remind recipients of the potential
for large irradiators to deliver life-threatening radiation doses when
safety and security systems are bypassed or preventive maintenance programs
are ignored. It is expected that licensees will review this information,
distribute and review it with all facility workers and radiation staff to
prevent similar incidents from occurring at their facility. Licensees are
also expected to consider actions, if appropriate, to ensure that adequate
preventative maintenance and proper safety training programs with periodic
retraining exists. However, suggestions contained in this notice do not
constitute any new NRC requirements; therefore, no specific action or
written response is required.
Description of Circumstances:
Several incidents of overexposure, resulting in loss of life, occurred
outside of the United States as a result of bypassing safety and security
systems and not following safety and operating procedures. However, at the
facility of an Agreement State licensee, a worker avoided overexposure by
following proper safety and operating instructions and procedures. In
another instance, during an inspection of an NRC licensee, violations noted,
including the bypassing of safety systems and the willful misleading of NRC
during the subsequent investigations, resulted in proposed civil penalties.
A more detailed description of these incidents is provided in Attachment 1.
9102270158
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IN 91-14
March 5, 1991
Page 2 of 3
Discussion:
As shown in Attachment 1, beliefs such as "no risk because the machine is
turned off" and actions such as using numerous ways to bypass safety and
security systems demonstrate a lack of knowledge of the nature of radiation,
as well as its danger. All supervisory personnel, particularly the
radiation safety officer, are reminded of their responsibility to ensure
safe operation at their facilities. The incidents described in the
attachment demonstrate the importance of:
1. Not bypassing interlocks and other safety systems
2. Following all authorized operating procedures
3. Training all involved personnel in safety and operational procedures,
with periodic retraining, stressing the need for operators to promptly
notify their supervisors when unusual or conflicting signals arise on
control systems
4. Maintaining all equipment in good working condition and promptly
repairing or replacing any defective or nonfunctional equipment
5. Complying with all regulatory requirements and license conditions
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate NRR project manager.
Richard E. Cunningham, Director
Division of Industrial and
Medical Nuclear Safety, NMSS
Technical Contact: Susan L. Greene, NMSS
(301) 492-0686
Attachments:
1. NRC Information Notice 89-82
2. Attachment 1
3. List of Recently Issued NMSS Information Notices
4. List of Recently Issued NRC Information Notices
.
Attachment 1
IN 91-14
March 5, 1991
Page 1 of 3
DESCRIPTION OF INCIDENTS AT LARGE IRRADIATOR FACILITIES
Case 1. (340,000 Ci Co-60 Irradiator in Israel) A transport jam occurred,
causing the transport mechanism to stop, the "source-down" signal to come
on, and the gamma alarm to sound. The sounding of the gamma alarm was
considered unusual. Acting against operating and safety instructions, the
operator did not notify his supervisor and instead handled the situation on
his own. He turned the alarm system off by disconnecting the console
cables, defeated the door interlock by cycling the power switch, unlocked
the door, and entered the radiation room. He did not check the Geiger
counter he carried before entering the radiation room, and consequently was
unaware that the instrument was not operational.
Seeing torn cartons, but unable to see that the source rack remained up
because it was resting on the edge of a carton, the operator got a cart and
began removing the damaged cartons. After about a minute, he began to feel
a burning sensation in his eyes and left the room. Since the operator was
not wearing his film badge, the whole body dose for the 1 1/2 to 2 minutes
he was in the radiation room was estimated to be about 1,000 to 1,500 rads.
The source rack was later released and lowered to the pool under the
direction of the supplier, and no further overexposures were reported. The
operator died from radiation exposure due to acute radiation syndrome
effects 36 days after the accident.
Case 2. (18,000 Ci Co-60 Irradiator in El Salvador) The sounding of the
source transit alarm alerted the night shift operator (Worker A) that the
source was neither fully up nor fully down as a result of a fault condition,
which should have caused the source rack to be automatically lowered to the
pool. He followed the reset procedure at the control panel, however had no
success in stopping the alarm and releasing the door. He tried to free the
source rack by detaching the normal regulated air supply and applying
overpressure to force the source rack into the fully raised position (a
procedure not recommended by the supplier). This attempt also failed. The
worker was eventually able to stop the alarm, but the general failure light
and the "source-up" light remained on. He then manipulated the microswitch
system to produce a "source-down" light.
Worker A disabled the door interlock system by rapidly cycling the buttons
on the radiation monitor panel, while turning the key in the door switch
(another procedure not recommended by the supplier), thus simulating the
detection of normal background radiation in the radiation room by the fixed
monitor and succeeded in opening the door. He then shut off the power
supply to the facility and entered the radiation room believing that, as
with unpowered X-ray equipment, there would be no continuing radiation.
Without first checking the radiation levels with a portable radiation
instrument, he began to remove the deformed product boxes that had jammed.
At this point he noticed that the
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Attachment 1
IN 91-14
March 5, 1991
Page 2 of 3
descent of the source rack was prevented by the slack cable of the hoist
mechanism. Unable to free the rack by himself, he left the radiation room
and turned the power back on, noticing that the failure light was "on" and
the "source-down" light was intermittent, but that no alarm was sounding.
Worker A then enlisted Workers B and C to help free the source rack. They
had no experience or knowledge of the irradiation facility. After assuring
Workers B and C that there was no risk as the machine was turned off, the
three men entered the radiation room and began removing the jammed product
boxes, while standing directly in front of the source rack. As the product
boxes were removed and the source rack was lowered to the surface of the
water, the workers noticed the blue glow in the pool from Cerenkov
radiation. Worker A was surprised at this and after fully lowering the
source rack, he told the others to exit quickly. When leaving the radiation
room, Worker A was questioned by Worker B as to the use of the portable
radiation monitor that was located some distance from the irradiator. He
explained that the instrument was for radiation detection and measurement,
but that it had not been necessary to use it.
Worker A became ill minutes after leaving the radiation room and was taken
to the hospital. Workers B and C later became ill and also went to the
hospital. The company was unaware of the accident for several days because
the workers were incorrectly diagnosed as having food poisoning. It was
later discovered that some of the source pencils had fallen from the source
rack into the pool and that one of the pencils had fallen into the radiation
room. At least four more persons were overexposed before the circumstances
of the accident were fully realized.
Worker A was hospitalized for extensive radiation burns to his legs and feet
and gastrointestinal and hematopoietic radiation syndrome. His right leg
was amputated and, 197 days after the accident, Worker A died as a result of
his radiation exposure.
Worker B was treated for symptoms of acute radiation exposure and severe
burns. After the amputation of both legs, he was transferred to a
rehabilitation facility 221 days after the accident.
Worker C suffered less severe symptoms of radiation exposure and remained on
sick leave from work for 199 days after the accident. Long term effects to
these workers may include eye damage from radiation exposure. A more
detailed description of the incident can be found in IAEA, Vienna, 1990
STI/PUB/847.
STI/PUB/847, IAEA Vienna, 1990. Copies can be obtained for reference and
training tools from UNIPUB, 4611-F Assembly Drive, Lanham, MD 20706-4391
.
Attachment 1
IN 91-14
March 5, 1991
Page 3 of 3
Case 3. (3.5 million Ci Co-60 Irradiator in an Agreement State) The
operator noticed that the product had received an unacceptably low dose. He
shut down cell operations and, with the source position monitor indicating
that the sources were down and the in-cell radiation monitor showing
radiation levels at zero, he entered the cell with a portable radiation
survey instrument. He noticed elevated radiation levels between 1-2 mR/hr
on the survey instrument and aborted his attempt to enter the cell. The
operator restricted the area and notified supervisory personnel.
Investigation into the cause of the elevated radiation readings revealed
that one of the source racks was not fully down and that the top of the rack
was about 1« feet from the top of the pool. An inspection of the winch
mechanism indicated that the cable brake had failed to stop the winch
allowing the cable to completely unwind. As a result, the source rack was
raised instead of lowered with the continuing rotation of the winch
mechanism. The source rack was then manually lowered into the pool. It was
determined that deterioration of the wiring in the Geiger-Muller tube of the
cell monitor due to radiation exposure was the cause of this system failing
to warn of the elevated radiation levels in the radiation room. The
necessary repairs were made to the control panel and the cell monitor and
procedures instituted to upgrade the safety systems of the facility. The
operator followed safety and operating procedures during the incident and
avoided overexposure by correctly using the portable survey instrument.
Case 4. (1.3 million Ci Co-60 Irradiator in NRC Jurisdiction) During an
inspection and subsequent investigation at an irradiator facility, NRC
identified the following violations, including but not limited to: (1)
failing to promptly and effectively repair the lock on the personnel-access
door to the irradiator cell; (2) modifying a procedure without first
obtaining NRC approval (i.e., replacing a safety component in the irradiator
start-up system), as was required in the license; and (3) the deliberate
bypassing of administrative procedures and safety interlock and physical
barriers to gain entry to the irradiator cell by climbing over the
irradiator cell access door. An NRC investigation also determined that
senior licensee management knew of the violations and made incomplete and
inaccurate statements to the NRC during an enforcement conference and the
subsequent investigations involving the circumstances of these violations.
The potential for extremely high radiation exposures and the licensee's lack
of candor with NRC raised questions about the ability and willingness of the
licensee to comply with NRC requirements. NRC considered these violations
of the safety requirements to be serious and proposed a civil penalty of
$13,000 be assessed against the licensee. Senior management involved in
this incident are no longer associated with the facility. The licensee has
instituted a Quality Assurance program and additional training requirements.
.
