Information Notice No. 84-61: Overexposure of Diver in Pressurized Water Reactor (PWR) Refueling Cavity
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
August 8, 1984
Information Notice No. 84-61: OVEREXPOSURE OF DIVER IN PRESSURIZED
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
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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
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
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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
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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
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
R. L. Pedersen, IE
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