Opening and closing of vessles (RPV, SG)

In the nuclear sector, a unit outages allow a reactor cover to be opened to replace the fuel and carry out mechanical and valve maintenance operations.

CMI has developed particular expertise in vessel opening and closure operations whatever the planned shutdown outage may be:

  • ASR  - simple refuelling shutdown 
  • VP - partial inspection
  • VD - decennial inspection

Opening phases

  • Stripping down of the vessel cover: removal of the anti-missile slab, removal of the heat insulation, interrupting of the thermocouples, removal of the vessel level, raising of the earthquake anchoring rods, raising of the cable bridge..
  • Placement of the vessel stud tightening and untightening machine (MSDG) on the cover of the reactor vessel. Untightening and unscrewing of the vessel studs to clean them.
  • Appraisal and cleaning of studs before greasing
  • Removal of the vessel cover and placement on its stand
  • Disconnection of command rods
  • Removal of upper internals (UI) and placement on stand
  • Unloading of fuel and storage in the spent fuel pit (fuel building)

Closure phases

  • Refuelling of the reactor's vessel
  • Placement of upper internals (UI) in vessel
  • Connection of command rods
  • Placement of the cover on the reactor's vessel
  • Placement of vessel stud tightening and untightening machine on the cover. Screwing down and tightening of the vessel studs.

Repositioning of the vessel cover, (lowering the cable bridge, lowering the earthquake anchoring rods, placing the thermocouples, placing the vessel level, placing the heat insulation, placing the anti-missile slab...)

  • Apart from the opening and closure of the vessels, CMI has developed other skills for the nuclear sector such as valve maintenance.


  • Maintenance on all types of reactor: 900 MW – 1300 MW – 1450 MW
  • Provision of additional staff expert in TVI: televisual inspections


  • High-performance teams and ongoing training
  • Certifications for maintenance operations in a nuclear environment