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Cutting techniques : the BR3 experience

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1 Cutting techniques : the BR3 experience
J. Dadoumont SCK•CEN J Dadoumont, SCK•CEN, Chapter 8 : cutting techniques

2 BR3, first PWR reactor in Europe, first PWR to be dismantled
BR3 : Belgian Reactor number 3 Type : Pressurized Water Reactor Started in 1962, shutdown in 1987 3582 EFPD in 11 campaigns Power : 10,5 Mwe Selected by the European Commission in 1989 as Pilot Project for the RTD program on Decommissioning Nuclear installations

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

4 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

5 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

6 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)

7 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.

8 One Belgian standard : 400 l drum
The cut pieces must match the material handling and evacuation requirements Output dismantling = Input material management One Belgian standard : 400 l drum

9 First cutting operation
The Thermal shield

10 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

11 The reactor pressure vessel and the 2 sets of internals

12 The strategy is to cut it in-situ

13 Underwater remote EDM cutting, Mechanical Cutting and Plasma arc torch must be compared

14 Plasma Arc torch cutting in a flooded chamber
Electro Discharge Machining, Mechanical Cutting and Plasma arc torch for the Thermal Shield Segment 540x500x76.2 mm Thermal Shield : 5.5 t SS304 In situ EDM In-situ Mechanical Sawing Plasma Arc torch cutting in a flooded chamber In situ EDM

15 Comparison of the Cutting Techniques during the Thermal Shield Work
Only relative values

16 Second cutting operation :
Dismantling of two sets of internals

17 The reactor pressure vessel and the 2 sets of internals

18 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

19 Two sets of Internals were dismantled
The Vulcain Internals: 8 years old The Westinghouse internals : 30 years old

20 Remote controlled underwater cutting has been extensively used
The Circular Saw The Bandsaw

21 All important operations started with: Cold testing in a test tank
Bandsaw Models Turntable

22 …followed by application in the reactor pool
Bandsaw frame Turntable Workpiece (core baffle)

23 We could compare immediate dismantling with defferred dismantling
No real significant gain was obtained in terms of dose uptake, waste management and technical feasibility After 30 years cooling period, the dose rate from the “old” internals is still high enough to request remote, shielded underwater operation To have a significant technology change 80 years would be necessary

24 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

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

26 Other underwater remote dismantling techniques were also used: surgery EDM

27 Other underwater remote dismantling techniques were also used: reciprocating saw

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

29 Other underwater remote dismantling techniques were also used: impact unbolting

30 Next cutting operation
The reactor pressure vessel

31 The BR3 Reactor Pressure Vessel some 39 years ago…
Hot and Cold legs Reactor Support Skirt

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

33 Underwater cutting or Dry cutting
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”

34 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.

35 The thermal insulation is fastened by a carbon steel shroud
Refueling pool NST Easy access to the fastening screws

36 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)

37 Then cutting the pipes short to the RPV flange (access through the pipe interior)

38 View of the prototype machine during cold testing
Available space: ~10 inches Thickness: ~4.5 inches

39 After one year preparation work, the RPV could be lifted
RPV is lifted as the water level rises

40 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 Band Saw Turntable Milling Cutter

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

42 The primary loop big components will be cut by HPWJC
Steam generator Pressurizer RPV cover RPV bottom Neutron Shield Tank (RPV support)

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

44 Dismantling of contaminated loops
The steam Generator Chamber

45 Dismantling in the primary loop area (containment building)
80 % of material free released Before After

46 ALARA principle put into practice: cutting in large pieces
Size reduction Cutting on site using an automatic tool Transport

47 ALARA principle put into practice: transportation outside of the area

48 ALARA principle put into practice: size reduction workshop outside of the area

49 Ventilated size reduction workshop

50 Dismantling of thin tank using the nibbler

51 Dismantling of high contaminated tank (no transport possible)

52 Handhold Mechanical cutting equipment for small contaminated pipes

53 The Steam Generator strategy required concrete cutting

54 Cutting of the concrete above the Steam Generator
The surfaces to cut were first decontaminated The diamond cable is an industrially proven technique

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