Information Notice No. 82-31: Overexposure of Diver During Work in Fuel Storage Pool
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D. C. 20555
July 28, 1982
Information Notice No. 82-31: OVEREXPOSURE OF DIVER DURING WORK IN FUEL
All nuclear power plant facilities holding an operating license (OL) or
construction permit (CP).
This information notice is provided as a notification of a significant,
whole-body exposure in excess of regulatory limits to a diver engaged in
underwater work in a fuel storage pool at a pressurized water reactor.
Licensees are using divers for an increasing number of maintenance and
inspection tasks and have demonstrated substantial exposure savings by using
proper underwater work techniques. However, this incident demonstrates the
potential for serious overexposures in very short time periods. Dose rates
from LWR spent fuel assemblies and other irradiated components can be
extremely high. A single spent fuel bundle can create a 104 - 106 R/hour
radiation field at close proximity. Irradiated objects (e.g., BWR fuel
channels) can read from ten to hundreds of R/hour on contact. It is expected
that licensees will review the information for applicability to their
facilities. No specific action or response is required at this time.
Description of Circumstances:
On June 1, 1982 while installing fuel rack support plates in the Indian
Point Unit No. 2 fuel storage pool, a contractor diver received an exposure
of about 8.7 rems to the head. A second diver, also working in the pool on
June 1, received a whole body dose of about 1.6 rems.
Upon exiting the pool the most highly exposed diver's 500 mR and 5-R pocket
dosimeters (worn on the head) were off-scale. The licensee suspended all
diving operations, read the multiple TLD's (thermoluminescent dosimeters)
worn on other body locations, and initiated an investigation of the
incident. The fuel storage pool modification work had been ongoing for about
three months, with daily exposures averaging about 50 millirems per diver.
A review of the incident by licensee and NRC personnel found several factors
that contributed to the overexposure:
(1) An irradiated fuel assembly was mistakenly transferred to a location
two to four feet from the subsequent divers' work location. A
poor-quality copy of the fuel transfer procedures was apparently a
factor in the improper fuel transfer. Limited visability in the pool
caused by cloudy
July 28, 1982
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water and a lack of pool underwater lighting may have prevented visual
detection of the misplaced fuel assembly. No QA (quality assurance)
reviews were required or conducted of the irradiated fuel assemblies
locations between fuel movements and the exposure incident.
(2) The prior-to-work radiation survey of the pool was performed with an ,
underwater ionization chamber connected by a long cable to the
detector. These surveys failed to detect the misplaced fuel assembly's
radiation field of several hundred R/hr within two feet of the divers
work area. Intermittent, erratic underwater survey instrument behavior
had been observed during previous dives. The licensee attributed the
survey instrument's erratic behavior to a buildup of moisture in the
underwater detector chamber housing.
(3) Radiation monitoring devices used during the underwater operations
failed to function properly. Alarming dosimeters, mounted inside the
divers' helmets, failed to alarm at the 200 mR set point. These
dosimeters were under the control of the diving contractor and were not
source checked on the day of the incident. The licensee monitored the
dive with the same ionization chamber instrument used for the pre-dive
survey, and failed to detect any radiation fields in excess of 1 R/hr
in the diver work area.
The licensee increased senior management oversight for the spent fuel pool
project and implemented the following corrective actions.
(1) Whenever fuel movement occurs, QA personnel will independently witness
and verify the new locations of the fuel assemblies. Other irradiated
objects greater than 1 R/hr on contact will be controlled in a similar
manner. After any movement of either fuel or irradiated components (>1
R/hr), an underwater radiation survey will be conducted before any
diving operations will resume.
(2) Daily, before any diving operation, a radiation survey of the diving
area will be conducted. This survey will be performed using two
independent radiation exposure monitoring devices. A survey map of the
pool will be updated to reflect current status of ongoing fuel rack
(3) Each diver will be equipped with a calibrated, alarming dosimeter; this
dosimeter will be checked each day before diving operations begin. Each
diver will also be equipped with a remote-readout radiation detector
which will be continuously monitored by health physics technicians. The
divers will surface and have their dosimetry checked periodically, any
significant deviation from the expected dive work pattern or radiation
levels will be grounds for dive termination.
(4) Fuel pool clarity and underwater lighting acceptance criteria have been
established to help ensure adequate visability is maintained.
July 28, 1982
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No written response to this information notice is required. If you need
additional information about this matter, please contact the Regional
Administrator of the appropriate NRC Regional Office.
Edward Jordan, Director
Division of Engineering and
Office of Inspection and Enforcement
Technical Contact: J. E. Wigginton
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