Information Notice 1990-33, Sources of Unexpected Occupational Radiation Exposures at Spent Fuel Storage Pools

Sources of Unexpected Occupational Radiation Exposures at Spent Fuel Storage Pools

ML031210552
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Crane
Issue date:	05/09/1990
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-90-033, NUDOCS 9005030120
Download: ML031210552 (7)

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.

IN 90-33

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.

..

.

.. ..

.

.. . ..

..

. ...

..

....

....

...

..

.......

....

OL

• Operating License

CP

• Construction Permit

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NUCLEAR REGULATORY COMMISSION

WASHINGTON, D.C. 2055

OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE, $300,

FIRST CLASS MAIL

POSTAGE & FEES PAID

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12055500395 6

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