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Cutting techniques : the BR3 experience

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

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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: 1999-2000 • 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. • The cutting technique must be compliant with the measuring apparatus

  8. 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 ofinternals

  12. The strategy is to cut itin-situ

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

  14. Electro Discharge Machining, Mechanical Cutting and Plasma arc torch for the Thermal Shield Thermal Shield : 5.5 t SS304 Segment 540x500x76.2 mm 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 ofinternals

  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. 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. Refueling pool NST The thermal insulation is fastened by a carbon steel shroud 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

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