United States Nuclear Regulatory Commission - Protecting People and the Environment

Overexposure of Diver During Work in Fuel Storage Pool

HPPOS-002 PDR-9111210075

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, June 04, 2015