Pellets / tablets of UO2 are used as fuel for PHWR & BWR nuclear reactors. In the reactors, heat generated in these pellets has to be taken out by the coolant water. To avoid the contact of UO2 with the coolant water, these pellets are filled inside sealed zirconium alloy tubes called fuel cladding to form fuel rods. The Zircaloy cladding not only encloses fuel pellets but also acts as the second barrier among four such barriers against the release of radioactivity into public domain. Zircaloy, which is an alloy of Zirconium with tin, iron and chromium as alloying elements, has been chosen to manufacture the fuel tubes since the alloy shows high corrosion resistance, low neutron absorption & high melting point. Fuel clad tubes are made to very stringent dimensional tolerances with respect to the Outer Diameter, Inner Diameter, wall thickness and also the impurity levels. Since the time of inception in the early 70’s NFC has established the facilities & processes and slowly and steadily increased the production of the zircaloy tubes meeting the stringent quality and quantity requirements of the Indian PHWR and BWR reactors for the customer NPCIL. NFC has time and again exhibited its competence to manufacture such critical components starting from the Refined Ore to all the core and structural components for the Indian nuclear reactors, to world quality standards.
Qualified Zirconium sponge and required quantity of alloying elements are compacted in hydraulic presses to obtain compacts / briquettes. These compacts are welded to each other by electron beam welding under vacuum to obtain a long cylindrical electrode.
Also, considerable quantity of Zircaloy scrap is generated at different work centres during the fabrication of fuel clad tubes and other components. Such scrap is chemically good and for recovering valuable metal content, this scrap is sized and cleaned and converted into rectangular cross sectional semi-fused electrodes.
These electrodes are melted multiple times by consumable electrode in vacuum arc re-melting furnace in water cooled copper crucibles, with intermediate stage machining for obtaining final ingots.
Zircaloy ingots are subjected to 1st stage of extrusion, machining and cutting. After making a hollow billet, it is subjected to beta-quenching, machining and 2nd stage extrusion in order to obtain a hollow blank. This hollow blank is stress relieved in vacuum and passed on for multi-stage pilgering with intermediate vacuum annealing etc. Tube finishing operations like straightening, grinding, cutting, etc. are also performed to obtain the requisite stringent quality.
For this purpose, NFC possesses state of the art fabrication facilities such as extrusion & piercing press, cold rolling mills, vacuum annealing furnaces, special surface finishing and treatment equipments are available to achieve the desired mechanical and metallurgical properties of cladding tubes.
Fuel rods are assembled together with components, like End plates, End Caps, Bearing Pads & Spacer Pads, to form a fuel bundle.
Bars required for manufacturing end plugs are produced by cold rotary swaging operation of the extruded bars in different passes with intermediate vacuum annealing, final straightening and centerless grinding to required sizes. As end plug acts as the first sealing of fission products, the produced bars undergo rigorous quality checks.
Zircaloy Ingot are extruded to slabs which are rolled to sheets. Bearing pads and spacer pads are punched out of these sheets.
For these, NFC is equipped with mechanical presses, Automatic Vibratory finishing system, centre lathe machines, automated machining centres, etc.
Automated Machining Center-
Automatic vibratory finishing systems -
Mechanical press