Three Mile Island Unit 2
Key Decisions and Important Events forRemoving the Damaged Fuel
Presented at the1st International Forum on the Decommissioning of theFukushima Daiichi Nuclear Power StationApril, 2016
Chuck Negin
Washington Grove, Maryland, USA
charlesnegin@gmail.com
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Damaged Fuel and Debris

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2Damage Examples

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Various Areas for Defueling Core Cavity
 Lower Support Grid
 Flow Distributor Behind and within the Core Baffle Plates
 Lower Head
 Elsewhere in the Reactor Systems

Bottom of the Upper Core Support Assembly

Reactor Pressure Vessel Cutaway View
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4Defueling Progress and Key Impacts
1982-1983
Defueling Options Evaluations

1982
First Video of Core

1983
Sonar Mapping &Improved Video

1983
First Sample

1984
Defueling Method Decision
Dry Canal & Mostly Manual

Vessel Defueling ProgressFeb-1990

100%May-1989

Mid-1984
Vessel Head Lift

Core Former
Disassembly90%
Lower Grid
Cutting80%

Dec-198870%
Dec-1987

60%
50%

Sept-1987

40%
30%

Lost Water Clarity

20%
10%

April-1987
Dec-1986

Feb-860%
Oct-1985
Oct-85
Apr-86

Nov-86May-87

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Dec-87

Jun-88Jan-89Aug-895Removal Methods
 Five concepts for fuel removal before visualcharacterization; none were used: Dual Telescoping Tube, Manipulator
 Manual Defueling Cylinder Indirect Defueling Cylinder Flexible Membrane
 Dry

 Later, a remotely operated service arm, shredder, andvacuum transfer system was considered and rejected Final method chosen was an adapted mining drill (thecore bore) and manual methods

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6Core Boring Machine Adapted from commercial mining drilling
equipment One of the most important machines for theproject First use with hollow core bits: 10 samples 1.8
m long x 6.4 cm diameter (figure below)
 Second use with solid face bits to chew throughthe hard once-molten mass in the core region
 Third use was assisting lower grid andinstrument tubes by grinding metal (nextviewgraph)

Tungsten Carbide Teeth with Synthetic Diamond
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7Fuel Removal Tools and Equipment
 Some Manual Tools
 Powered Equipment
 Core Boring Machine Plasma Arc
 Power Assisted shears
 Bulk Removal
 Water Vacuum and Air Lift

 Manual ControlledEquipment
 Grippers
 Buckets

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Work Platform

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Three Canister Design – 341 Shipped

271 Fuel & Debris Canisters

10 Knockout Canisters(for vacuum tools)
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60 Filter Canisters(water processing)10

Packaging & Transport

Canister Staging in Spent Fuel Pool

Transfer Cask Operations
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Staging & Shipping

Loading the Shipping Cask

Shipping Cask
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12Packaging, Transport, & Storage at Idaho
Idaho
NationalLaboratory

3400 kmThree Mile Island

1986 to 1990
341 canisters of fuel & debris in46 shipments by rail cask to theIdaho National Laboratory
1990 to 2000Wet Storage in Spent Fuel
Storage Pool
2000 – 2001
Removed from pool, dewatered,dried, and placed in dry storage
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13Possible Remaining Fuel ParticulateResidual Fuel* RPV: < 900 kg
 In the Reactor Coolant System: < 133 kg Criticality ruled out by analysis
Assessment Required a Combination of* Video inspection for locations
 Gamma dose rate and spectroscopy
 Passive neutron solid state trackrecorders, activation, BF3 detectors
 Active neutron interrogation
 Alpha Detectors
 Sample Analysis

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14Events/Decisions(1)Events/Decisions
Decisions for removal
required visualcharacterization

SignificanceFirst idea of what conditions really were; complete assessment
took another year; could not proceed to plan defueling without
this knowledge
Decision to not to install• New application for the proposed technology, concern thatin-core shredding
failure would cause problems, relied mostly on manual
equipment in the vessel
manipulation with power assist• Allowed defueling to start earlier, knowing that overall
schedule would not be minimized. This was preferred over a
3 year development for a remote system/equipmentDecision to leave refueling • Less depth for manually operated tools
canal dry• Shielded work platform 2m above the reactor pressure vessel
flange• Reduced need for water processing• Dose rates were low within the refueling canalUse of Core Boring• Samples of the fuel and debris that was melted together
Machine was essential• Breaking up the crust and molten mass when manual
methods were unsuccessful
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15Events/Decisions(2)Events/Decisions
Unanticipated biological
growth in water fouled
filters
DOE to take Fuel & Debris
New cask design andlicenseShip Fuel to Idaho by Railand not Truck

SignificanceCaused a year delay; managing water clarity is extremely
important

Transfer to Dry Storage

Long term storage stability, also allowed demolition of fuel poolat Idaho••••

Handling and shipping design and fabrication could not takeplace until destination was determined
Allowed fuel & debris canisters to be removed from TM
New cask could be designed for the TMI canisters
Fewer shipments

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