Information Notice 1995-56, Shielding Deficiency in Spent Fuel Transfer Canal at a Boiling-Water Reactor

Shielding Deficiency in Spent Fuel Transfer Canal at a Boiling-Water Reactor
	ML031060207
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, Three Mile Island, 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
Issue date:	12/11/1995
From:	Crutchfield D; Office of Nuclear Reactor Regulation
To:	;
References
	IN-95-056, NUDOCS 9512060021
	Download: ML031060207 (11)
	v • d • e

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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 December 11, 1995 NRC INFORMATION NOTICE 95-56: SHIELDING DEFICIENCY IN SPENT FUEL

TRANSFER CANAL AT A BOILING-WATER REACTOR

Addressees

ATI holders of operating licenses or construction permits for nuclear power

reactors.

Purpse

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information

notice to alert addressees to an event at a boiling-water reactor where the

mishandling of highly activated materials in the flooded spent fuel transfer

canal caused unexpectedly high radiation fields in a hallway under the canal.

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 are not

NRC requirements; therefore, no specific action or written response is

required.

DescriDtion of Circumstances

On November 11, 1994, contractors were conducting underwater operations in the

Unit I spent fuel pool In the cutting tool working area at the Edwin I. Hatch

Nuclear Plant (Inspection Report 50-321/95-01 and 50-366/95-01 [Accession

Number 95021400811)--cutting coupons out of spent control rod blades

containing the upper guide roller bearings (see Attachment 1). The highly

activated Stellite bearings '(some measured as high as 160 sievert [16,000 rem]

per hour at 30 centimeter,'[12 inches] under water) were being collected

adjacent to the Unit 1 work area. Periodically, the coupons containing the

upper guide roller bearings were transferred from the collection bucket to a

cask liner in the shipping cask storage area in the Unit 2 spent fuel pool.

When the workers could not find the tool to open the liner, they decided to

transfer the coupons in the collection bucket (about half full, with 160 -

coupons) into another bucket for temporary storage, so that the cutting

.process could continue. To facilitate the task, the offload wiT performed in

the transfer canal since the canal was much shallower than the fuel pools.

During the transfer, some of the coupons fell to the bottom of the transfer

canal. Since the transfercanal was designed and routinely used as-a transit

area for highly activated material, including spent fuel, the workers were not

concerned about dropping the coupons and saw no need to notify the unit shift

foreman or the control room of the incident. They recovered the coupons from

the bottom of the canal and placed them in the storage bucket resting on the

canal floor.

Po& I (E %509kct AS nos& IST IZlL

9512060021 1E

3fA/Ce

IN 95-56 i;J December 11, 1995 About 30 minutes after the coupons were dropped, a plant equipment operator

was walking through the Unit I (56.4-meter [185-foot] elevation) hallway

directly under the transfer canal (see Attachment 2), when his digital alarm

dosimeter alarmed on high dose rate (set at 0.5 msievert [50 mrem] per hour).

The plant equipment operator left the area promptly and notified a health

physics supervisor, who sent a health physics technician to the area. When

the health physics technician also found the elevated radiation levels

described above, he secured the area, investigated for the source of the high

radiation levels, and informed shift management. The licensee measured

radiation levels of up to 1 sievert [100 rem] per hour on contact with the

hallway ceiling directly below the bottom of the canal, and 0.05 to 0.1 stevert [S to 101reml per hour inthe general area of the hallway. The plant

equipment operator received a dose equivalent of about 0.1 msievert (10 urem]

from the event. The licensee has always required that all personnel entering

the radiological controlled area be issued dosimeters. Before alarm

dosimeters were required, all workers entering the radiologically controlled

area were issued personal dosimeters (non-alarm), so any doses to workers from

this shielding deficiency would have been detected and accounted for as part

of the routine dosimetry program.

In response to the event, Hatch Nuclear Plant management instituted procedural

controls to prohibit the use of the transfer canal until doors had been

installed, in order to exclude worker access to the affected hallway. Before

the transfer gates are allowed to be lifted (allowing use of the transfer

canal), the doors at each end of hallway under the canal are locked, and

access to the hallway is controlled as a very high radiation area, as defined

in 10 CFR 20.1602, Control of Access to Very High Radiation Areas.'

At the Limerick Generating Station recently, the licensee took the initiative

to reevaluate the adequacy of its spent fuel pool shielding before commencing

the reracking of its Unit 2 fuel pool. A thorough engineering review examined

the radiation levels in the accessible areas under the spent fuel pool and

associated transfer canals and cask pit area. This review revealed (using

conservative shielding assumptions) that a dropped spent fuel bundle could

create a high radiation area in areas below the cask wash pit that were

accessible to personnel. Before commencing fuel movement, the Limerick staff

established precautionary radiological controls (posted as high radiation

area/radiation work permit required for entry) and radiation monitoring

(portable area radiation monitor) for the affected area.

Discussion

A portion of the shielding directly under the transfer canal at Hatch Nuclear

Plant isinadequate to prevent unacceptable external dose rates in the hallway

below, should a highly activated component be placed near, or in contact with, the canal floor (with attendant loss of water shielding). Therefore, even

with a successful bucket-to-bucket transfer (no dropped coupons), with the

loaded bucket stored and resting on the canal floor, the hallway radiation

levels would have-been essentially the same as for the actual event.

Many licensees perform spent fuel pool modifications and major cleanup

activities involving handling and moving large quantities of highly activated

IN95-56

'

'VDecember 11, 1995 materials, including spent fuel. In general, the industry has significantly

improved its awareness of and controls for potentially high and very high

radiation areas caused by operational mishaps (e.g., dropping a spent fuel

bundle in the transfer canal directly over the upper drywell in a boiling- water reactor, and the hazards of withdrawn incore thimbles under the reactor

vessel at pressurized-water reactors). Initiatives such as those taken by the

Limerick Station should help prevent unexpected, uncontrolled worker exposures

with the potential for exceeding the regulatory limits. A thorough prejob

evaluation of activities involving highly activated (or potentially highly

activated) components can help identify challenges to existing plant

shielding.

Thbs 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 Office of

Nuclear Reactor Regulation project manager.

L r4 u t rec or

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Jim Wigginton, NRR

(301) 415-1059 Roger Pedersen, NRR

(301) 415-3162 Wade Loo, RII

(404) 331-2831 Attachments:

1. Under Water Operations Event in the

Spent Fuel Pool At Hatch

2. Unexpected High Radiation Area at Hatch

3. List of Recently Issued NRC Information Notices

-- OF7S>.r

,Stellfte Coupon Movement Top of Typical Control Rod

Handle

Upper Guide

Roller (4)

0

00

0 0)

c

0 0

Shipping Cask 0 0

Storage Area

(Poot Wter Depth - 39-ft) 0 0

"-7- Stelflte

Coupon

Coupon Is About 1.25" on Edge.

Steltite Ban Is About %0 DIa.

Transfer HeI(

Canal Unit 1 Xte9 Depth - 24 ft)

(Pwow

I 0 V1!00'

g.4,

0" C

Underwater Operations Event in the -

Spent Fuel Pool at Hatch F ' .0W

W

q.o

%O

%A

ATTACHMENT 2 IN 95-56 December 11, 1995 Floor Elevation 228'

Normal Pool Elevation 227'

Spent

Fue1 Pcol Transfer Canal

M

3As Steel Plate

Elevation 203'

-I-

100 Rem/h on Contact

Hal way

5-10 Remlh

General Area

. Floor Elevation185'

Unexpected High Radiation Area at Hatch

I chment 3

"ni5-56 December 11, 1995 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

9g-55 Handling Uncontained 12/06/95 All Uranium Recovery

ThTTowcake Outside of a Licensees.

Facility Processing

Ciruit

Decay Heat Management 12/01/95 All holders of OLs or CPs

Practices during for nuclear power reactors.

Refueling Outages

g-53 Failures of Main Steam 12/01/95 All holders of OLs or CPs

Isolation Valves as a for nuclear power reactors.

Result of Sticking

Solenoid Pilot Valves

95-47, Unexpected Opening of a 11/30/95 All holders of OLs or CPs

Rev. I Safety/Relief Valve and for nuclear power reactors.

Complications Involving

Suppression Pool Cooling

Strainer Blockage

94-13, Control and Oversight of 11/28/95 All holders of OLs or CPs

Supp. 2. Contractors during Re- for nuclear power reactors.

fueling Activities and

Clartficaiton of Applica- bility of Section 50.120 of

Title 10 of The Code of

Federal Regulations to

Contractor Personnel

95-13, Potential for Data 11/22/95 All holders of OLs or CPs

- Supp. I - .Colettin.Equipment-to

. for nuclear power reactors.

Affect Protection System

Performance

91-29, Deficiencies Identified 11/22/95 All holders of OLs or CPs

Supp. 3 during Electrical for nuclear power reactors.

Distribution System

Functional Inspections

OL = Operating License

CP - Construction Permit

IN 95-56 December 11, 1995 materials, including spent fuel. In general, the industry has significantly