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Experience gained during the manufacture of duct assemblies for annular linear induction pump of PFBR

  • Posted on: 27th October, 2023

Annular Linear Induction Pumps (ALIP), working on electromagnetic principle are used for pumping the liquid metal sodium in auxiliary circuits such as fill and drain and purification circuits of sodium cooled fast breeder reactors. Although the pumping efficiency of these pumps are low, they are used in fast reactor circuits owing to their high reliability and low maintenance due to the absence of any moving parts.

IGCAR has developed electromagnetic pumps of various capacities and successfully tested and used them in experimental facilities. This paper highlights the methodology adopted for the manufacturing and helium leak testing of duct assemblies for the 170 m3/h capacity ALIP for use in PFBR Secondary Sodium Fill and Drain Circuit (SSFDC).

The pump is a reflux type of pump with both inlet and outlet on the same side. Duct assemblies were manufactured from SS316L hollow bars and pipe for a maximum sodium operating temperature of 450ºC.

As these duct assemblies are critical components of the ALIP, it demanded an established manufacturing procedure in order to achieve the required dimensional & geometrical tolerances and leak tightness.

Outer and inner ducts were precisely machined from hollow bar, with intermediate heat treatment to relieve the residual stresses and dimensional stability and finally by vertical honing process. One end of outer duct was closed using formed torispherical dished end and other end was connected to delivery line.

All the guided butt weld joints were subjected to non-destructive testing viz. LPT, RT as per ASME Section V. The inner duct was packed with CRGO laminated thin sheets with packing density of more than 95 percentages.

To ensure the integrity of the weld joints, the inner duct assembly was subjected to pneumatic pressure testing (external) at 2 MPa (g) and helium leak testing under vacuum was carried out in accordance with ASME code requirement separately as well as assembled with outer duct assembly.

A systematic assembly procedure was established and followed during manufacturing of outer duct in order to achieve high quality and reliability. Maintaining of annular gap between these outer and inner duct assemblies throughout the length within the specified tolerances was really a challenging task (as change in this gap severely affect the sodium flow characteristics) and was realized with hard faced centring pads welded to the outer periphery of the inner duct assembly.

Nickel hard facing of components to minimize the wear and tear of the mating components such as spacers, centring pads, front centring pads and outer periphery of the porous shell were done using plasma transferred arc process and qualified as per nuclear industry specification.

This article is shared by T. Saravanan, M. Krishnamoorthy, S. Surendar Kumar, S. Murugan, S. Sathees Kumar, B.S. Ramesh Babu, V. Praveen Kumar, Utpal Borah, Alka Kumari, G. Ramesh, M. V Kuppusamy, Prashant Sharma and Basant Kumar Nashine of Central Workshop Division, Engineering Services Group & Quality Assurance Division, Safety, Quality and Resource Management Group, IGCAR, Kalpakkam

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