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1 Cutting techniques : the BR3 experience J. Dadoumont SCKCEN J Dadoumont, SCKCEN, Chapter 8 : cutting techniques.

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Presentation on theme: "1 Cutting techniques : the BR3 experience J. Dadoumont SCKCEN J Dadoumont, SCKCEN, Chapter 8 : cutting techniques."— Presentation transcript:

1 1 Cutting techniques : the BR3 experience J. Dadoumont SCKCEN J Dadoumont, SCKCEN, Chapter 8 : cutting techniques

2 2 BR3, first PWR reactor in Europe, first PWR to be dismantled 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 EFPD in 11 campaigns3582 EFPD in 11 campaigns Power : 10,5 MwePower : 10,5 Mwe Selected by the European Commission in 1989 as Pilot Project for the RTD program on Decommissioning Nuclear installationsSelected by the European Commission in 1989 as Pilot Project for the RTD program on Decommissioning Nuclear installations

3 3 BR3 Pilot Project: main cutting operations Remote cutting of the thermal shield: Dismantling of highly active internals: 2 sets 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 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 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 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 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. The cutting technique must be compliant with the measuring apparatus

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

9 9 First cutting operation The Thermal shield

10 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 11 The reactor pressure vessel and the 2 sets of internals

12 12 The strategy is to cut it in-situ

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

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

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

16 16 Second cutting operation : Dismantling of two sets of internals

17 17 The reactor pressure vessel and the 2 sets of internals

18 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 19 Two sets of Internals were dismantled The Vulcain Internals: 8 years old The Westinghouse internals : 30 years old

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

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

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

23 23 We could compare immediate dismantling with defferred dismantling No real significant gain was obtained in terms of dose uptake, waste management and technical feasibilityNo 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 operationAfter 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 necessaryTo have a significant technology change 80 years would be necessary

24 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 25 Other underwater remote dismantling techniques were also used: hydraulic cutter

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

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

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

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

30 30 Next cutting operation The reactor pressure vessel

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

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

33 33 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 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 35 The thermal insulation is fastened by a carbon steel shroud Easy access to the fastening screws

36 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 37 Then cutting the pipes short to the RPV flange (access through the pipe interior)

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

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

40 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 Milling Cutter Turntable Band Saw

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

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

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

44 44 Dismantling of contaminated loops The steam Generator Chamber

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

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

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

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

49 49 Ventilated size reduction workshop

50 50 Dismantling of thin tank using the nibbler

51 51 Dismantling of high contaminated tank (no transport possible)

52 52 Handhold Mechanical cutting equipment for small contaminated pipes

53 53 The Steam Generator strategy required concrete cutting

54 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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