Information Notice No. 90-33: Sources of Unexpected Occupational Radiation Exposures at Spent Fuel Storage Pools

                                UNITED STATES
                           WASHINGTON, D.C.  20555

                                 May 9, 1990

                                   RADIATION EXPOSURES AT SPENT FUEL STORAGE 


All holders of operating licenses or construction permits for nuclear power 


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 radiation exposures were encountered in 
the activities associated with SFS pools.  

Events Involving Highly Radioactive Objects That Floated in SFS Pools

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 
underwater vacuuming system floated at least 15 feet toward the top of the 


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fuel racks at the Peach Bottom Atomic Power Station.  Licensee personnel 
speculated 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 SFS Pools

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 immediately 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.  


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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 of Highly Radioactive Material by Hoist

In April 1982 at the Peach Bottom Atomic Power Station, Unit 2, personnel 
inadvertently 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 preparation 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 exposed 
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 of the tool is under water and near a highly 
radioactive source.  


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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.  


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 
radiological control considerations can help minimize the possibility of 
unexpected exposures from radiation sources in SFS pools:  

x    Thorough evaluations of the contents of, and activities involving, SFS 
     pools from a radiological perspective to identify potential unexpected 
     exposure situations. 

x    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 

x    Measures to ensure awareness of the need for thorough radiation surveys 
     of all materials being removed from SFS pools.  

x    Measures to eliminate or secure floatable material in SFS pools. 

x    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.  

x    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.  

x    Measures to ensure awareness of the need to prevent radiation streaming 
     through hollow sections of handling tools. 

x    Enhanced use of alarming personal dosimeters and of alarming area 
     radiation monitors around SFS pools. 


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This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate NRR project 

                              Charles E. Rossi, 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 

1.  Documents Providing Information on Events 
      Involving Spent Fuel Storage Pools 
2.  List of Recently Issued NRC Information Notices 

                                                            Attachment 1
                                                            IN 90-33
                                                            May 9, 1990
                                                            Page 1 of 1

             Documents Providing Information on Events Involving
                          Spent Fuel Storage Pools

James A. FitzPatrick, June 1989 Event 

x  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 

x  Memorandum from R. R. Bellamy, Region I, to L. J. Cunningham, NRR, 
   August 16, 1989.  

Millstone Unit 1, May 1987 Event 

x  Inspection Report No. 50-245/87-11, July 1, 1987.  

Diablo Canyon, December 1987 Event 

x  Inspection Report No. 50-275/88-01, February 12, 1988. 

x  LER 87-27-00 (Docket No. 50-275). 

Byron, October 1989 Event 

x  Inspection Report No. 50-454/89-21, December 8, 1989. 

James A. Fitzpatrick, February 1987 Event 

x  Inspection Report No. 50-333/87-07, March 11, 1987. 

x  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 

x  Inspection Report No. 50-483/89-16, September 8, 1989. 

Peach Bottom, April 1982 Event 

x  Inspection Report No. 50-277/82-11, July 13, 1982.  

Indian Point Unit 3, July 1989 Event 

x  Inspection Report No. 50-286/89-18, September 12, 1989.  


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