FABRICATION OF TUNGSTEN AND TUNGSTEN-MOLYBDENUM ALLOY TUBING

THIS PROJECT IS TO DEVELOP A NEW METHOD OF FABRICATING LONG LENGTHS OF PIPE FROM EXOTIC METALS. THE METHOD IS PARTICULARLY ATTRACTIVE FOR METALS THAT ARE DIFFICULT TO WORK WITH BECAUSE OF BRITTLENESS OR EXTREMELY HIGH SOFTENINGTEMPERATURES. FOR DOE, THE NEW TECHNIQUE IS TO BE APPLIED TO THE FABRICATION OF TUNGSTEN TUBING. SUCH TUBING IS NEEDED TO HANDLE CORROSIVE LIQUIDS USED DURING THE PROCESSING OF NUCLEAR FUEL FOR SEVERAL ADVANCED NUCLEAR REACTOR CONCEPTS. AT PRESENT, TUNGSTEN TUBING FOR THIS APPLICATION IS FABRICATED ONLY BY GUN DRILLING, IN WHICH A LONG DRILL BIT BORES OUT A HOLE IN A CIRCULAR BAR. GUN DRILLING, HOWEVER, LIMITS THE TUBING LENGTH TO ABOUT 8 FEET AND REQUIRES LARGER-THAN-DESIRED TUBING WALL THICKNESS. MOREOVER, GUN DRILLING CANNOT BE USED ON TUNGSTEN, THE MATERIAL OF CHOICE; A MOLYBDENUM-TUNGSTEN ALLOY IS USED INSTEAD, WITH REDUCED CORROSION RESISTANCE BEING A CONSEQUENCE. THE NEW TUBE FABRICATION TECHNIQUE IS ESPECIALLY ATTRACTIVE FOR THIS DOE APPLICATION BECAUSE IT CAN BE READILY APPLIED TO PURE TUNGSTEN, AS WELL AS TO MOLYBDENUM-TUNGSTEN ALLOY. WALL THICKNESS CAN BE REDUCED AND CONTROLLED, AND IT IS EXPECTED THAT THE TUBE LENGTH CAN BE MUCH GREATER THAN THE PRESENT LIMIT OF 8 FEET. ALSO, THETUBING IS FABRICATED FROM COMMERCIALLY AVAILABLE STOCK MATERIAL, SO THAT THE PHYSICAL PROPERTIES OF THE FINISHED PRODUCT ARE WELL CHARACTERIZED. IN PHASE I OF THE PROJECT, THE FEASIBILITY OF THE INNOVATIVE BORING TECHNIQUE APPLIED TO PURE TUNGSTEN WILL BE DEMONSTRATED, INCLUDING STRAIGHTNESS OF THE BORE, BORING RATE, AND SURFACE CHARACTERISTICS. SAMPLES WILL BE AVAILABLE FOR INSPECTION AT THE END OF PHASE I. PHASE II WORK WILL INVOLVE SCALE-UP OF THE PHASE I PROCESS.