Calandria Assembly

1
  •    Calandria assemblies and associated components
  •    NPCIL
  •      GHAVP 1&2, Haryana
  •      2
  •     Nuclear Division

Description

The Calandria is an open stepped cylindrical vessel which forms the heart of the nuclear reactor. It is completely filled with heavy water during operation, and houses the coolant channel - fuel rod assemblies. It has 122 nozzles for absorber rod and control rods. Alignment and concentricity of nozzles with the nozzles housings is crucial for proper functioning of absorber and control rod mechanisms.

Construction details

Materials:

  • Shell: SA 240 TYP 304L
  • Nozzle Forgings: SA 182 F304L

Dimensions:

  • Outside diameter of main shell: 7.8m
  • Length of main shell: 4.6 m
  • Thickness of main shell: 32mm

Critical aspects

  • 1. Contamination Control: It is crucial to maintain complete separation between stainless steel and carbon steel manufacturing. Any contact with carbon steel could result in damage to corossion resistant properties of stainless steel
  • 2. Distortion Control: The Calandria is highly prone to distortion due to the extremely large D/t ratio and the material properties of stainless steel. Only low heat input welding techniques can be used, with proper cooling arrangement to prevent distortion. The sequence of nozzle opening and welding has to be properly determined , and welding has to be carried out in a balanced manner. Spiders and other jigs and fixtures have to be designed to maintain shell ovality
  • 3. Nozzle Concentricity and alignment: The nozzle-housing concentricity is crucial to enable proper functioning of control and absorber rod mechanisms. Shrinkages have to be determined using a mockup and sufficient allowances have to be made to ensure nozzle concentricity and alignment with housing