Information Notice 1990-33, Sources of Unexpected Occupational Radiation Exposures at Spent Fuel Storage Pools
I/
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555 May 9, 1990
NRC INFORMATION NOTICE NO. 90-33:
SOURCES OF UNEXPECTED OCCUPATIONAL RADIATION
EXPOSURES AT SPENT FUEL STORAGE POOLS
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
This information notice is intended to alert addressees to potential sources of
unexpected occupational radiation exposures at spent fuel storage (SFS) pools.
It is expected that recipients will review the information for applicability
to their facilities and consider actions, as appropriate, to avoid similar
problems. However, suggestions contained in this information notice do not
constitute NRC requirements; therefore, no specific action or written response
is required.
Description of Circumstances
SFS pools provide a water-shielded location for the storage of spent fuel and
other highly radioactive materials that are potential sources of high radiation
exposures. SFS pools also may be contaminated with highly radioactive particles
having activities of tens of millicuries (mCi) or more. This information notice
identifies a number of events in which sources of unexpected occupational radi- ation exposures were encountered in the activities associated with SFS pools.
Events.Involving-Highly.Radioactive-Objects-That Floated ip SFS-Paols
In June 1989, several individuals involved in SFS pool cleanup activities at
the James A. FitzPatrick Nuclear Power Plant received unexpected radiation
exposures (within NRC limits) from an object floating near the surface of
the SFS pool near their work location. Subsequent radiation surveys of the
object indicated contact radiation exposure rates of about 1000 roentgens per
hour (R/hour). The licensee believes that the source of the radiation was a
small fragment of radioactive material imbedded in a piece of floating material.
The floating material probably was a piece of a 5-gallon polyethylene container
in which irradiated components had been stored underwater for more than a year.
Apparently, the polyethylene container began to disintegrate as a result of
radiation from the irradiated components stored inside it.
The problem of contaminated objects floating to the surface of SFS pools is
not new. In December 1984, complete canister filters from a portable under- water vacuuming system floated at least 15 feet toward the top of the spent
9005030120
IN 90-33 May 9, 1990 fuel racks at the Peach Bottom Atomic Power Station.
Licensee personnel specu- lated that the filters may have surfaced and then sank to the spent fuel storage
racks.
Although no personnel received unexpected exposures, this event could
have caused significant exposure to personnel.
In May 1987, floating vacuum cleaner filters were also involved in a similar
event at the Millstone Nuclear Power Station, Unit 1. During that event, the
radiation level on the refueling floor increased momentarily to more than 100
mR/hour, then quickly returned to a normal level of about 10 mR/hour.
The high
radiation level occurred at the same time that the spent fuel pool cooling system
was returned to use following valve maintenance.
Refilling of the system forced
air into the SFS pool through the sparger. The bubbles rose in the pool, causing
agitation. The licensee postulated that the agitation forced highly contaminated
vacuum cleaner filter cartridges stored in the pool to the surface. These filters
contained debris from past cleaning evolutions of the reactor vessel and were
suspended by nylon line in the SFS pool. After this event, the licensee decided
to remove disposable items from the pool and to replace nylon lines, used for
suspending items in the pool, with wire cables.
Events.Involving .Highly .Radioactive-Particles-or.Fragments-of Radioactive
Material Removed from. SVS.ools
During reracking operations in the SFS pool at the Diablo Canyon Nuclear Power
Plant, Unit 1, in December 1987, a highly radioactive particle (45.5 mCi of Co-60)
was inadvertently removed from the SFS pool. The particle was attached to an air
grinder hose that was partially pulled from the pool by the diver tender when the
grinder hose became entangled with the diver's hose. When the Co-60 particle was
removed from the pool, the radiation from the particle caused the fuel handling
building (FHB) area radiation monitor to alarm, resulting in a shift of the FHB
ventilation system to the iodine removal mode. The air grinder hose was not
monitored for radiation while it was being removed from the pool.
Conservative
estimates by the licensee indicated that had the diver tender come in contact
(0.5 second) with the Co-60 particle with his hands, he could have received an
extremity dose of 895 mrem.
In October 1989, personnel at the Byron Station found unexpectedly high activity
Co-60 particles (8 mCi and 77 mCi) during efforts to decontaminate and remove a
portable filter assembly that had been used in an underwater vacuum cleaner to
clean the bottom of the SFS pool. Three individuals received unexpected doses
to their hands and forearms from these highly radioactive particles. These doses
were calculated to be 1.25, 1.95, and 11.6 rem.
Highly radioactive materials also have been lifted, unexpectedly, to the surface
of SFS pools. At the FitzPatrick plant in February 1987, a worker received an
overexposure to the hand during the cutting and removal of in-core instrumentation
dry tubes from the reactor vessel.
During this operation, the cutting tool was
removed from the water for inspection. A piece of highly radioactive dry tube
that had been stuck in the tool fell out on the refueling floor. A worker im- mediately picked up the piece of dry tube and threw it back into the water. As
a result of this brief contact with the dry tube, the worker received a radiation
dose of about 30 rem to his hand, which exceeds the NRC limit of 18.75 rem per
calendar quarter.
IN 90-33 May 9, 1990 At the Callaway Plant, personnel discovered that an inadequate survey had been
made on an underwater fuel elevator following its removal from the SFS pool on
April 23, 1989. On April 29, 1989, a metal object was found to read 1000 R/hour
at contact, but the object was shielded by the elevator structure so that only a
localized area exceeded 100 mR/hour. The highly radioactive metal object was
found to be a piece of a torn grid strap from a fuel assembly that had been
repaired in the fuel elevator on April 21, 1989.
Personnel had attempted to
flush the piece out of the bottom of the fuel basket. However, because the
piece was never seen in the fuel elevator basket and because no abnormal radiation
readings were reported, personnel incorrectly assumed that the piece had been
flushed from the elevator basket and was at the bottom of the fuel pool.
Event Involving Inadvertent Lifting-.f-Mlghly-Radicactive-Materialby.Moist
In April 1982 at the Peach Bottom Atomic Power Station, Unit 2, personnel in- advertently lifted a highly radioactive (in the million R/hour range) control
rod blade (CRB) near the surface of the water for 5 to 10 seconds. This event
occurred when a hafnium test blade (HFB) was to be moved from the fuel prepara- tion machine to a CRB rack location. This evolution was being supervised by a
senior licensed operator. When an operator attempted to move the HFB using the
fuel grapple, the operator could not engage the temporary C clamp on the HFB.
An auxiliary hoist was subsequently used to successfully move the HFB to the
CRB rack location. After completing the HFB movement, the operator proceeded
to pull the hoist grapple to its normal storage location out of the water.
While the hoist was rising, its grapple engaged and picked up an adjacent CRB.
The hoist limit switch stopped the upward movement when the grapple was still
under 8 to 10 feet of water. At that time the operator, without looking, used
the 'override" button to bypass the limit switch and raised the grapple with
the attached CRB. The area radiation monitor started alarming as the grapple
with the CRB approached the surface of the water. Upon hearing the alarm, the
refueling floor supervisor looked and saw a brown object approaching the water
surface and yelled, "Put it down, put it down." The grapple was stopped before
the CRB reached the surface.
No radiological surveys were performed during
this evolution. However, individuals at the pool area were unnecessarily ex- posed to radiation. Although these doses were about 300 mrem or less, if the
CRB had reached the surface, the doses could have been much greater.
Event Involving Radiation Streaming
Underwater tools are designed with flood holes to allow water to fill the
hollow sections of tubes. These flood holes provide shielding against
radiation streaming from highly radioactive materials that are stored
under water. At Indian Point Station, Unit 3, in July 1989, a worker
using a tool to perform reconstitution of a spent fuel assembly noticed
that a 12-foot-long 3/4-inch-diameter hollow section of the tool did not
have a flood hole. As a result of this equipment design deficiency, the
worker received an unplanned exposure. Although the licensee estimated
that the worker received a radiation dose of only 30 mrem as a result of
this incident, a hollow tool filled with air rather than water can result
in much higher doses when the lower end bf the tool is under water and near
a highly radioactive source.
IN 90-33 May 9, 1990 Additional -Information:
Additional information on these events is provided in the documents listed in
Attachment 1. The NRC and licensee documents are available in the NRC Public
Document Room.
Discussion:
Although the events described above were associated with SFS pools, similar
problems can occur during the removal and handling of material from flooded
reactor cavities.
A review of licensee evaluations of these events, the licensee corrective
actions, and feedback from NRC inspectors indicate that the following radio- logical control considerations can help minimize the possibility of unexpected
exposures from radiation sources in SFS pools:
O
Thorough evaluations of the contents of, and activities involving, SFS
pools from a radiological perspective to identify potential unexpected
exposure situations.
o
Measures such as task analysis and training to ensure awareness of the
potential for uncontrolled, unplanned transfer of highly radioactive
materials, including highly radioactive particles, to the surface of
SFS pools with the attendant potential for high radiation exposure of
workers.
o
Measures to ensure awareness of the need for thorough radiation surveys
of all materials being removed from SFS pools.
o
Measures to eliminate or secure floatable material in SFS pools.
o
Avoidance of the use of containers made of materials (particularly
plastics) that are subject to radiation damage and disintegration
for the storage of highly radioactive materials in SFS pools.
If
such containers are used, limiting the radiation dose to the container
can be used to prevent disintegration of the container as a result of
radiation damage.
o
Measures to ensure that highly radioactive objects stored under water
at one end of a line whose other end is secured above the surface of
the pool are not unexpectedly pulled to the surface.
o
Measures to ensure awareness of the need to prevent radiation streaming
through hollow sections of handling tools.
O
Enhanced use of alarming personal dosimeters and of alarming area radia- tion monitors around SFS pools.
May 9, 1990 This information notice requires
you have any questions about the
of the technical contacts listed
no specific action or written response.
If
information in this notice, please contact one
below or the appropriate NRR project manager.
C ariles- ~E. i1, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts:
John D. Buchanan, NRR
(301) 492-1097
Ronald L. Nimitz, RI
(215) 337-5267 Attachments:
1. -Documents Providing Information on Events
Involving Spent Fuel Storage Pools
2. List of Recently Issued NRC Information Notices
s_
Attachment 1
IN 90-33 May 9, 1990 Documents Providing Information on Events Involving
Spent Fuel Storage Pools
James A. FitzPatrick, June-1989-Event
° Inspection Report Nos. 50-333/89-08, August 10, 1989; 50-333/89-13, August 2, 1989; and 50-333/89-21, December 29, 1989.
Peach Bottom, -December-1984 Event
o Memorandum from R. R. Bellamy, Region I, to L. J. Cunningham, NRR,
August 16, 1989.
Millstone Unit-1, May 1987-Event
O
Inspection Report No. 50-245/87-11, July 1, 1987.
Diablo Canyon,-December-1987.Event
o Inspection Report No. 50-275/88-01, February 12, 1988.
° LER 87-27-00 (Docket No. 50-275).
Byron, October 1989-Event
o Inspection Report No. 50-454/89-21, December 8, 1989.
James-A. Fitzpatrick, .February-1987 Event
° Inspection Report No. 50-333/87-07, March 11, 1987.
o Letter from John C. Brons, New York Power Authority, to the Director, Office of Inspection and Enforcement, NRC, May 21, 1987.
Callaway.-April- 1989-Event
O
Inspection Report No. 50-483/89-16, September 8, 1989.
Peach Bottom,-April 1982.Event
o Inspection Report No. 50-277/82-11, July 13, 1982.
Indian Point Unit-3,-July-1989-Event
° Inspection Report No. 50-286/89-18, September 12, 1989.
t..
Attachmpnt
2 IZ 90-33 May 9. 1990
Page I of I
LIST OF RECENTLY
ISSUED
RRC INFORMATION
NOTICES
Date CT
, .ssau.ce
Tntorniron
IssaeW.te.
lotic NoR.
Subject
90-32
Surface Crack and Subsurface
Indications
in the Weld of
A Reactor
Vessel Head
90-31
Update on Waste Form and
High Integrity Container
Topical Report Review
Status. Identification
of Problems with Ceount
Solidification. and
Reporting of Waste Mishaps
90-30
Ultrasonic Inspection
Techniques for Dissimilar
Metal Welds
90-29
Cracking of Cladding and
Its Heat-Affected Zone in
the Base metal of a Reactor
Vessel Head
90-28
Potential Error In High
Steamline Flow Setpoint
90-27
ClarifIcation of the
Recent Revisions
to the
Regulatory Requirements
for Packaging
of Uranisum
Hexafluoride (UF6 ) for
Transportation
89-70,
Possibla
Indications
of
Supp. I
Nsirepresented
Vendor
Products
90-25 Inadequate
Flow of
Essentiel Service
Water
to Room Coolers and Heat
Exchangers for Engineered
Safety-Feature System
5/3/90
5/4/90
5/11/90
4/30/9C
Issueedt ....
e
.
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLS
or CPs for nucleer
power reectors.
fuel
cycle licenses, and
certain by-product
materials
licenses.
All holders
of OLS
or Cps for nuclear
power reactors.
All holders of OLs
or Cps for nuclear
power reactors.
4,30/90
All holders of OLs
or CPs for 3WRs.
4/30/90
All uranium fuel
fabrication and
conversion facilities.
4/26/90
Ali holders of OLS
or Cps for nuclear
power reactors.
4/24/90
All holders of OLs
or Cps for nuclear
power reactors.
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.. ..
.
.. . ..
..
. ...
..
....
....
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..
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- Construction Permit
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