United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

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

Page Last Reviewed/Updated Thursday, March 29, 2012