Information Notice No. 84-61: Overexposure of Diver in Pressurized Water Reactor (PWR) Refueling Cavity

                                                            SSINS No.: 6835 
                                                            IN 84-61       

                                UNITED STATES
                           WASHINGTON, D.C. 20555

                               August 8, 1984

                                   WATER REACTOR (PWR) REFUELING CAVITY 


All nuclear power plant facilities holding an operating license (OL) or 
construction permit (CP). 

Purpose and Summary: 

This information notice is provided to inform recipients of a whole-body 
exposure in excess of regulatory limits to a diver engaged in underwater 
repair work. At the Palisades Nuclear Generating Plant on March 18, 1984, a 
diver received a whole-body exposure totaling about 4.5 rems to his right 
thigh during a series of three dives while working on the fuel transfer tilt
machine (upender) in the flooded reactor refueling cavity. The dose received
during the first two dives totalled about 1 rem. Failure to account for the 
diver's change of work position relative to a known, high level radiation 
source during the third dive caused this whole-body overexposure. The diver 
kneeled in a layer of radioactive sludge on the tilt pit floor. 

This diving event is the second instance in which a lack of adequate 
management and radiological controls for planned underwater work led to a 
diver receiving a whole-body overexposure. After reviewing this and the 
previous event (described in IE IN 82-31, July 28, 1982), the NRC staff has 
developed further guidance to help licensees properly control and manage 
underwater work to prevent overexposures. 

It is expected that licensees will review the information provided for 
applicability to their facilities and consider taking actions, as 
appropriate, at their facility. Suggestions and guidance contained in this 
information notice do not constitute NRC requirements and, therefore, no 
specific action or written response is required. 

Description of Circumstances: 

The refueling cavity side upender was found in need of repair (one leaking 
hydraulic hose). Underwater surveys in the upender area taken on March 16 
indicated radiation dose rates of 350 to 900 mrems/hour. An RWP was written 
on March 17, but no ALARA review was conducted for the repair work. 
Underwater radiation survey instrument malfunctions delayed starting the job
until March 18. Before the first dive, check surveys indicated underwater 
dose rates in the upender work area ranging from 1,000-7,000 mrems/hour. The
difference between these survey results and the March 16 results 
demonstrates the large 


                                                            IN 84-61      
                                                            August 8, 1984 
                                                            Page 2 of 4   

dose rate gradients in the work area and the difficulty in accurately 
positioning the survey instrument. Diving operations commenced March 18 on 
the afternoon shift. The diver was equipped with thermoluminescent 
dosimeters (TLDs) and self-reading dosimeters, but no continuous readout 
alarming dosimeter or dose rate survey instrument was required by the RWP. 
After each of the first two dives, the diver's TLDs were read and these 
exposure results along with the planned dive durations were used to 
establish a conservative, allowable stay-time for the following dive. The 
TLD results indicated an exposure of about 3.6 rems to the diver's thigh had 
been received during the third dive (twice the expected dose for the third 
dive). When informed of the diver's exposure the duty health physicist 
stopped all diving operations and began an investigation of the incident. 


A review of the incident by the licensee and NRC regional personnel found 
several key factors that contributed to the overexposure. 

1.   Lack of Job Planning and Controls 

Contrary to licensee administrative procedures, no formal ALARA review was 
performed and no maintenance work order was generated for the repair work. 
According to licensee representatives, had an ALARA review been performed, 
the resultant RWP would have required the diver to have a dose rate survey 
instrument with him at all times. The RWP did not stipulate further survey 
requirements. The plant radiation protection (RP) staff responsible for 
on-the-job supervision of the repair work received no formal, prework 
briefing. Shift turnover between the RP technicians covering the job was 
ineffective. No formalized RP procedure existed to detail special 
precautions, equipment, survey requirements, job-specific training, and 
other requirements conducive to effective RP coverage for this repair work. 

2.   Inadequate Surveys and Instrumentation 

Except for the prework surveys taken on March 16, none of the upender area 
underwater surveys performed before the incident were documented. On March 
18, underwater check surveys taken before the first dive indicated dose 
rates up to seven times (7,000 mrem/hour) the March 16 prework survey 
results, but this was not documented or reported to responsible RP 
supervision. The Palisades RWP procedure requires that a job be stopped if 
unplanned changes in the working environment occur. Evidently, information 
regarding these higher dose rates were not turned over to the oncoming RP 
relief crew. 

A diver was not used to obtain representative work area surveys. Contrary to
the Technical Specification requirement (6.12) for controlling individuals 
entering high radiation areas, the diver was not required to have a dose 
rate monitoring device in the work area to warn of unexpected changes in 
dose rates. The underwater survey instrument (a large-volume ion chamber 
with a 40 ft cable) was difficult to use effectively, hard to position 
precisely, and repeatedly malfunctioned. Because of its demonstrated poor 
performance and 

                                                            IN 84-61      
                                                            August 8, 1984 
                                                            Page 3 of 4   

fragile condition, the RP technicians reportedly tended to limit its use. 
The instrument's large volume (7.5 in. long and 5 in. in diameter) made it 
too cumbersome to reach into the cramped areas around the upender. 

After each dive, the diver's dosimeters were processed and the results were 
used for planning the next dive. As was expected by the licensee, the 
diver's dosimetry results for all three dives indicated an extreme dose 
gradient over the body. However, the licensee failed to account for the 
diver's different work position/posture for the third dive. The diver was 
much closer to a known radioactive source -- a sludge-like contamination 
layer on the tilt pit floor. While kneeling on the floor during the third 
dive, the diver's thigh area was in a 10-15 rem/hour radiation field for 
about one-half of the dive time. 


The nuclear industry uses divers to perform a variety of maintenance and 
repair tasks. The potential for significant exposures in very short periods 
of time demands stringent work and radiation protection controls. Water 
shielding offers dose savings, but it also presents difficulties in 
accurately assessing the dose rates in work areas. Extreme dose rate 
gradients allow highly localized areas of radiation to go undetected unless 
extremely detailed, carefully conducted surveys are performed. Finally, 
another unique problem is that the diver can move through the water shield. 
This factor adds another dimension to the RP control problem. 

Since the 1982 diver overexposure, several licensees have requested guidance
for improving their radiological control program to support diving 
operations. Review of the procedures of several commercial diving companies 
disclosed that they contain many of the following elements: 

1.   A specialized written procedure for diving operations to ensure 
     effective radiological coverage and control. This procedure establishes
     minimum prerequisites in job planning, RP coverage requirements, survey
     technique/frequency, worker training, prework briefing, periodic RWP 
     updating, placement of dosimeters, etc. 

2.   During diving operations, continuous coverage is provided by qualified 
     RP technicians. These technicians have stop-work authority and clear 
     management guidance on when to exercise this important control 

3.   Minimum acceptance criteria is established for pool water clarity and 
     underwater lighting to help ensure adequate working area visibility. 

4.   The underwater work area is decontaminated if contamination presents a 
     significant exposure potential. 

5.   When practicable, physical barriers are provided to prevent diver 
     access to fuel/irradiated components and other high-radiation areas. 
     Diving cages or work platforms can successfully limit a divers mobility 
     to a well surveyed and controlled area. Special warnings (e.g., 
     underwater colored lights) can be used to mark high-dose-rate 
     areas/components. Each diver is equipped with a safety line and 
     continuous voice communication with 

                                                            IN 84-61      
                                                            August 8, 1984 
                                                            Page 4 of 4   

     surface personnel. Emergency procedures for diver rescue are provided 
     and understood by everyone involved in the diving operations. 

6.   Diver access control is planned to avoid traveling over or near 
     high-radiation areas. 

7.   Before any diving operation, a radiation survey of the diving area is 
     conducted using two independent radiation exposure monitoring devices. 
     Survey instruments are functionally checked (response checked) daily 
     before diving operations. TLDs can be used to help confirm dose rate 
     instrument readings. A survey map of the area is updated to reflect 
     current status of ongoing work. 

8.   Underwater confirmatory surveys of the work area are performed by the 
     diver. Because of the difficulty in placing a survey instrument from 
     the surface, underwater surveys by a trained diver are more effective 
     in locating hot spots. 

9.   After any movement of spent fuel or other highly radioactive 
     components, an underwater radiation survey is conducted before any 
     diving operations resume. 

10.  Each diver is equipped with a calibrated, alarming dosimeter which is 
     functionally checked each day before diving operations begin. 
     Additionally, each diver is equipped with a remote-readout radiation 
     detector which can be continuously monitored by health physics 
     technicians, or each diver carries a dose rate survey instrument. 
     Individual dose rate monitoring capability is necessary because of the 
     dose rate gradient of the water. The divers surface and have their 
     dosimeters checked periodically; any significant deviation from the 
     expected dive work pattern or radiation levels are grounds for 
     terminating the diving operations and reassessing the conditions. 

No written response to this information notice is required. If you require 
any additional information about this matter, please contact the Regional 
Administrator of the appropriate regional office or this office. 

                                   Edward L. Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  J. E. Wigginton, IE
                    (301) 492-4967

                    R. L. Pedersen, IE
                    (301) 492-9425

List of Recently Issued IE Information Notices

Page Last Reviewed/Updated Wednesday, March 24, 2021