1 cutting techniques : the br3 experience j. dadoumont sckcen j dadoumont, sckcen, chapter 8 :...
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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