Overexposure of Diver During Work in Fuel Storage Pool
HPPOS-002 PDR-9111210075
Title: Overexposure of Diver During Work in Fuel Storage
Pool
See IE Information Notice No. 82-31 entitled as above and
dated July 28, 1982. This notice cautions power reactor
licensees about radiation hazards to divers working in
spent fuel storage pools.
On June 1, 1982, while installing fuel rack support plates
in the storage pool at Indian Point Unit No.2, a diver
received a dose equivalent of 8.7 rem to the head. Upon
exiting the pool the diver's 500-mR and 5-R pocket
ionization chambers (worn on the head) were off-scale. The
licensee suspended all diving operations and read the
multiple TLDs worn on other body locations. A second diver
received a total body dose of 1.6 rem. The fuel storage
pool modifications had been ongoing for three months, with
daily averages for dose equivalent to total body of about
50 mrem per diver.
A review of the incident by the licensee and NRC found
several factors that contributed to the overexposure:
1. An irradiated fuel assembly was mistakenly
transferred to a location within two to four feet of the
diver's work area. A poor-quality copy of the fuel
transfer procedures was apparently a factor in the improper
fuel transfer. Limited visibility caused by cloudy water
and a lack of underwater lighting may have prevented visual
detection of the misplaced fuel assembly. No QA reviews
were required or conducted of the irradiated fuel
assemblies between fuel movement and the exposure incident.
2. A prior-to-work radiation survey of the pool was
performed with an underwater ionization chamber connected
by a long cable to the detector. The survey failed to
detect the misplaced fuel assembly and exposure rate of
several hundred R/hr within two feet of the diver's work
area. Intermittent, erratic behavior of the survey meter
had been observed during previous dives, and the licensee
attributed the erratic behavior to a buildup of moisture in
the housing for the underwater ionization chamber.
3. The radiation monitoring devices used during the
underwater operations failed to function properly.
Alarming dosimeters, mounted inside the diver's helmet,
failed to alarm at the 200-mR set point. These dosimeters
were under the control of the diving contractor and were
not checked with a source on the day of the incident. The
licensee monitored the dive with the same ionization
chamber instrument used for the predive survey and failed
to detect exposure rates in excess of 1 R/hr in the diver's
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. Other
irradiated objects with exposure rates of more than 1 R/hr
at contact will be controlled in a similar manner. After
any movement of either fuel or irradiated components (more
than 1 R/hr at contact), an underwater radiation survey
will be conducted before diving operations will resume.
2. Daily, before any diving operation, a radiation
survey of the diving pool will be made. Such surveys will
be performed with two independent monitoring devices. A
survey map of the pool will be updated to reflect current
status of the ongoing fuel rack modification
3. Each diver will wear a calibrated, alarming
dosimeter that will be checked daily before any diving
operations, and a remote-readout detector that will be
monitored continuously by health physics technicians.
Divers will also surface periodically and their pocket
ionization chambers will be read. Any significant
deviation from expected work patterns or radiation levels
will be grounds for dive termination.
4. Pool clarity and underwater lighting acceptance
criteria have been established to help insure adequate
visibility is maintained at all times.
Regulatory references: 10 CFR 20.201, 10 CFR 20.1501,
Regulatory Guide 8.38
Subject codes: 6.5, 7.1, 8.1
Applicability: Reactors