FABRICATION OF ZIRCALOY-2 CLAD URANIUM-12 WT PCT MOLYDENUM FUEL RODS
During the initial development of fuel elements for the PWR, the use of clad metallic-fuel rods was investigated. Design criteria were that the fuel and cladding must be metallurgically bonded for proper heat transfer, and the fuel, cladding, and diffusion zone between the fuel and cladding must be corrosion resistant. U-12 wt.% Mo was selected as the fuel material because it had shown exceptional corrosion resistance for a uranium-rich alloy; Zircaloy-2 was chosen as the cladding material because of its excellent corrosion resistance and low thermal neutron cross section. Coextrusion of the fuel and cladding alloys was the method selected to produce these cylindrical fuel elements. The metallurgical bonding of the fuel and cladding was accomplished by placing a right-circular cylinder of the fuel alloy in a tubular section of Zircaloy-2, encasing these components in a steel jacket, and extruding the assembly at an elevated temperature. The extruded rods were reduced to final size by cold drawing and were made corrosion resistant by etching 0.004 in. from the rod diameter. Stock for fuel components was extruded from duplex cast U-12 wt.% Mo ingots 4 in. in diameter and weighing 60 lb. Wrought fuel was found to be superior to east fuel because: (1) the billet assemblies utilizing wrought fuel did not require as much extrusion pressure as did assemblies with cast fuel, and because (2) the elements produced from wrought fuel were more dimensionally uniform than those produced from cast fuel because of the more uniform grain size of the wrought material. The Zircaloy-2 cladding components were machined from cups which had been produced by the back extrusion of bar stock. The Ti-Namel steel assembly packets were made by spinning. The fuel and cladding were assembled into extrusion billets by inserting them in the steel jackets with several accessory components and then sealing the jackets by welding in an inert- gas filled chamber. Fuel rods were fabricated by heating the assembled billets for 15 min at 1635 F in an 85% BaCl/sub 2/-15% NaCl salt bath and extruding to 0.437-in. or 0.500-in. diam rods. The steel jackets were removed from the extruded rods by pickling in an aqueous 50% HNO/sub 3/ solution. The rods were finished by cold drawing to 0.304-in. diam and etching to the final size of 0.300- in. diam. Dimensional uniformity of the fuel rods was aided by maintaining a temperature control of sintering time 5 F and a uniform billet loading time during extrusion. Front end defects associated with coextrusions were reduced from an average of 16 in. to 5 in. by the use of a separate steel front plug. The dimensional requirements for the finished element were a fuel diameter of 0.240 sintering time 0.005 in. with local variations not to exceed sintering time 0.009 in. from the nominal. A statistical analysis of the fuel diameter data from a group of fuel rods produced from 15 billets showed the average fuel diameter to be 0.2360 in. The 95% confidence limits for the process were 0.2345 in. to 0.2366 in.; the 99.9% confidence limits were 0.2349 in. to 0.2371 in. Statistical calculations showed that 91.6% of ths individual measurements met the specification for local variations. (auth)
- Research Organization:
- Westinghouse Electric Corp., Pittsburgh
- NSA Number:
- NSA-13-013575
- OSTI ID:
- 4253235
- Journal Information:
- Am. Inst. Mining Met. Petrol. Engrs., Inst. Metals Div., Spec. Rept. Ser., Vol. Vol: 5, No. 7; Other Information: Orig. Receipt Date: 31-DEC-59
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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Related Subjects
BARIUM CHLORIDES
BONDING
COATING
COLD WORKING
CONTROL
CORROSION
CROSS SECTIONS
CYLINDERS
DEFECTS
DIES
DIFFUSION
DRAWING
ETCHING
EXTRUSION
FABRICATION
FUEL ELEMENTS
FUELS
FUSED SALTS
GRAIN SIZE
HEAT TRANSFER
HEATING
HIGH TEMPERATURE
INERT GASES
JACKETS
MEASURED VALUES
MOLYBDENUM ALLOYS
NITRIC ACID
PLANNING
PRESSURE
SEALS
SODIUM CHLORIDES
SOLUTIONS
STABILITY
STANDARDS
STATISTICS
STEELS
THERMAL NEUTRONS
TITANIUM ALLOYS
URANIUM ALLOYS
VARIATIONS
VOLUME
WELDING
ZIRCALOY