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Cutting techniques : the BR3 experience

J. Dadoumont

SCK•CEN

J Dadoumont, SCK•CEN, Chapter 8 : cutting techniques

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BR3, first PWR reactor in BR3, first PWR reactor in Europe, first PWR to be Europe, first PWR to be

dismantleddismantled

• BR3 : Belgian Reactor number 3BR3 : Belgian Reactor number 3

• Type : Pressurized Water ReactorType : Pressurized Water Reactor

• Started in 1962, shutdown in 1987Started in 1962, shutdown in 1987

• 3582 EFPD in 11 campaigns3582 EFPD in 11 campaigns

• Power : 10,5 MwePower : 10,5 Mwe

• Selected by the European Commission in 1989 as Pilot Selected by the European Commission in 1989 as Pilot Project for the RTD program on Decommissioning Nuclear Project for the RTD program on Decommissioning Nuclear installationsinstallations

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BR3 Pilot Project: main cutting operations

• Remote cutting of the thermal shield: 89-91

• Dismantling of highly active internals: 2 sets 91-95

• Dismantling of contaminated loops and equipments: 95-

• Dismantling of the Reactor Pressure Vessel: 1999-2000

• D&D of RPV Cover and bottom, NST, SG, Pressurizer: 2001-

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Three main cases

• The contact dose rate of the piece to cut is high. Operator may not “touch” the piece to cut. Important shielding is required.

This requires a remotely controlled cutting technique (shielded workshop, underwater cutting…). Nevertheless we used almost industrially proven techniques.

The conception work is then focused on the remote deployment and maintenance of the technique.

The maintenance of the equipment must be compatible with the deployment strategy

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Three main cases (2)

• “Low” contact dose rate but high level of contamination More attention is focused on the cutting environment

and on the personal safety equipment of the operator

On site withdrawal “Production” size reduction workshop Some distinction must be made between

inside/outside contamination

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Three main cases (3)

• No (very very low) dose rate and no contamination Production becomes a priority Safety aspects are “only” classical safety ones Techniques used in industry (oxygen cutting, plasma arc,

grinding, industrial automatic bandsaw or reciprocating machine)

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The cutting technique in function of the destination of

the material

• The HLW and ILW (contact dose rate >2mSv/h): require radiological protection and special evacuation ways & procedures (very expensive). The cutting technique will produce as less secondary waste as

possible

• The LLW (important volume): most of them can be decontaminated up to a "free release" level, or can be reused or recycled. The cutting technique must be compliant with the decontamination

technique The cutting technique must be compliant with the measuring apparatus

• The VLLW, representing the largest volume and including the decontaminated LLW, are intended to be free released. The cutting technique must be compliant with the measuring apparatus

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The cut pieces must match the material handling and

evacuation requirements

Output dismantling = Input material management

One Belgian standard : 400 l drum

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First cutting operation

The Thermal shield

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The Thermal Shield

• The objective was to apply actual high active case cutting techniques in order to compare them in a “nuclear” point of view

• The first aspect of this internal component is its specific activity (up to 1 Cu/Kg)

Both impose us to work remotely underwater

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The reactor pressure vessel and The reactor pressure vessel and the 2 sets ofthe 2 sets of internalsinternals

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The strategy is to cut itin-situ

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Underwater remote EDM cutting, Mechanical Cutting and Plasma arc

torch must be compared

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Electro Discharge Machining, Electro Discharge Machining, Mechanical Cutting and Plasma arc Mechanical Cutting and Plasma arc

torch for the Thermal Shieldtorch for the Thermal Shield

In-situIn-situ

MechanicalMechanical

SawingSawing

In situ EDMIn situ EDM

Plasma Arc torch cuttingPlasma Arc torch cutting

in a flooded chamberin a flooded chamber

Segment 540x500x76.2 mmSegment 540x500x76.2 mmIn situ EDM

Thermal Shield : 5.5 t SS304

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Comparison of the Cutting Comparison of the Cutting Techniques during the Thermal Techniques during the Thermal

Shield WorkShield Work

PPaarraammeetteerr CCuuttttiinngg MMeetthhoodd

CCuuttttiinngg SSppeeeedd OOppeerraattiioonn DDuurraattiioonn

DDoossee UUppttaakkee

SSeeccoonnddaarryy WWaassttee VVoolluummee

MMeecchhaanniiccaall

11 11 11 11

PPllaassmmaa 5500 00..6633 11 55

EEDDMM 11//1100 44 33 55

Only relative valuesOnly relative values

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Second cutting operation :

Dismantling of two sets of internals

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The reactor pressure vessel and The reactor pressure vessel and the 2 sets ofthe 2 sets of internalsinternals

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Main features of the internals (from a D&D point-of-view)

• High radioactivity level (up to 4 Ci/kg implying a contact dose rate higher than 10 Sv/h)

• Complex geometrical shapes

• Very different thicknesses (from 1.6 mm up to 200 mm for some flanges)

• Different materials for some pieces

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Two sets of Internals were Two sets of Internals were dismantleddismantled

The Vulcain Internals: 8 years oldThe Vulcain Internals: 8 years old The Westinghouse internals : 30 years oldThe Westinghouse internals : 30 years old

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Remote controlled underwater cutting has been extensively

used

• The Circular SawThe Circular Saw

The Bandsaw

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All important operations started with:

Cold testing in a test tank

Models

Bandsaw

Turntable

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…followed by application in the reactor pool

Bandsawframe

Turntable

Workpiece(core baffle)

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We could compare immediate We could compare immediate dismantling with defferred dismantling with defferred

dismantlingdismantling

• No real significant gain was obtained in terms No real significant gain was obtained in terms of dose uptake, waste management and of dose uptake, waste management and technical feasibilitytechnical feasibility

• After 30 years cooling period, the dose rate After 30 years cooling period, the dose rate from the “old” internals is still high enough to from the “old” internals is still high enough to request remote, shielded underwater request remote, shielded underwater operationoperation

• To have a significant technology change 80 To have a significant technology change 80 years would be necessaryyears would be necessary

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In general, we used proven industrial techniques and mostly mechanical ones...

• This proved to be very reliable

• The total dose uptake for the whole dismantling of the 2

complete sets of internals was lower than 300 man-mSv

• The flexibility of the technique as well as an easy

maintenance is a real advantage, in terms of dose, cost

and time

• Proven technology avoids to have the “youth illnesses”

in such a difficult environment

• The techniques were only adapted to work remotely in

nuclear environment and underwater

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Other underwater remote Other underwater remote dismantling techniques were dismantling techniques were also used: hydraulic cutteralso used: hydraulic cutter

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Other underwater remote dismantling Other underwater remote dismantling techniques were also used:techniques were also used:

surgery EDMsurgery EDM

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Other underwater remote dismantling Other underwater remote dismantling techniques were also used: techniques were also used:

reciprocating sawreciprocating saw

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Other underwater remote dismantling Other underwater remote dismantling techniques were also used: core techniques were also used: core

drillingdrilling

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Other underwater remote dismantling Other underwater remote dismantling techniques were also used:techniques were also used:

impact unboltingimpact unbolting

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Next cutting operation

The reactor pressure vessel

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The BR3 Reactor Pressure Vessel

some 39 years ago…

Hot andCold legs

Reactor Support Skirt

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The strategy is a “one piece withdrawal” of the RPV into

the refuelling pool

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Studied strategies

• Underwater cutting or Dry cutting technical feasibility; radiation protection; safety; including the

case of equipment failure the shielding needs to cope with the

radioprotection requirements

• In-situ cutting or “One piece removal”

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The selected strategy

• “One piece removal” followed by an underwater dismantling: Reuse of the tools from the internals

dismantling Access to the thermal insulation and its

shroud easier (from the outside)• But,

A lot of preparation works are required to remove safely the RPV from its pit.

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The thermal insulation is fastened by a carbon steel

shroud

Easy access to the fastening screws

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Four main operations to separate the RPV

• 1. Separation from the bottom of the refuelling pool (hands on plasma torch)

• 2. Removal of the thermal insulation around the primary pipes (asbestos!)

• 3. Separation, from the legs

• 4. Separation from the NST (pneumatic tool with extended rod)

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Then cutting the pipes short to the RPV flange (access through

the pipe interior)

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View of the prototype machine during cold testing

Available space: ~10 inches

Thickness: ~4.5 inches

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After one year preparation work, the RPV could be

lifted

RPV is lifted as the water level rises

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Reactor Pressure Vessel Dismantling

•Cylindrical shell: Cut into 9 rings using horizontal milling cutter (tangential steps)•Flange: Cut with Bandsaw •Rings: Cut with Bandsaw into segments

Milling Cutter

Turntable

Band Saw

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Cold tests of milling cutter for the horizontal cutting of the RPV

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The primary loop big components will be cut by

HPWJC• Steam

generator• Pressurizer• RPV cover• RPV bottom• Neutron

Shield Tank (RPV support)

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Presently, cold tests are carried out to set up the cutting and

deployment system

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Dismantling of contaminated loops

The steam Generator Chamber

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Dismantling in the primary loop area (containment building)

80 % of material free released

Before After

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ALARA principle put into practice: cutting in large

pieces

Cutting on site using anautomatictool

Size reduction

Transport

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ALARA principle put into practice: transportation

outside of the area

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ALARA principle put into practice: size reduction

workshop outside of the area

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Ventilated size reduction workshop

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Dismantling of thin tank using the nibbler

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Dismantling of high contaminated tank

(no transport possible)

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Handhold Mechanical cutting equipment for small contaminated pipes

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The Steam Generator strategy required concrete cutting

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Cutting of the concrete above the Steam Generator

The surfaces to cut were first decontaminated

The diamond cable is an industrially proven technique