Plutonium Fuel Fabrication

[Music] fabrication of plutonium fuel and test pieces is complicated by consideration of criticality pyro forty and radioactive toxicity plutonium emits approximately five million times as many alpha particles as uranium 238 and forms a finely divided oxide powder with a remarkable ability to remain airborne its handling reflects the fact that it is thousands of times more toxic than industrial poisons this film was made in the Argonne fuel fabrication facility during manufacture of EBR one mark for fuel elements these elements consist of a circular tube containing plutonium slugs centered by means of coined ribs above and below the plutonium are blanket slugs of natural uranium and the assembly is completed by a hollow zirconium spacer and inconel x spring the annulus is filled with a heat conducting knack eutectic and the tube is completely sealed by a welded end fitting fabrication takes place within sealed hoods operating at a slightly negative atmospheric pressure raw plutonium in tin cans enters the production line through a pair of airlock hoods and a vinyl pouch which is purged with helium from here on the hoods contain filtered recirculating helium to prevent oxidation or combustion here and several times during production the plutonium is weighed for accountability handling and transfer between containers is accomplished with various tools to minimize the spread of contamination and glove contact with plutonium operations involving fragments chips or dust such as the initial cleaning by wire brushing are carried on in additional plastic enclosures to assist in retaining small particles the clean raw billet is broken to small size in a 50-ton press and loose or flying pieces are retained by a telescoping pillbox shield fragments recycle material and process scrap are sealed in tin cans for removal from the system the cans are brought out through a vinyl pouch which is heat sealed and cut free this operation both sealed the package and maintains the integrity of the production line Virgen plutonium and aluminum are weighed out for the appropriate alloy together with scrap from previous castings they are melted in a tantalum crucible supported by a graphite secondary crucible the crucible assembly is mounted on a pneumatic Ram and lowered into position in the center of the heating coil over the crucible hang a bundle of yttrium oxide coated precision bore Vicor tubes the upper end sealed and the lower end open above the melt cooling water circulating in coils around the furnace bail is pumped at sub-atmospheric pressure in case of accidental rupture helium is drawn into the coolant line preventing leakage of water into the hood the system is evacuated and the crucible raised to dip the molds in the molten plutonium as the furnace is repressurized with helium the gas forces metal up into the molds and the crucible is again lowered after breaking the glass molds away the castings are rough cut to produce slugs 2 and 1/8 inches long and the scrap rod return for remelt the slugs are coined and densified in a double plunger die at 180 thousand pounds per square inch to produce the final diameter and longitudinal ribs the fuel slugs are annealed at 400 degrees centigrade in a vacuum tube furnace before machining to final length the lathe is mounted on its side for convenient access to the controls and a plastic hood collects turnings finished fuel is inspected for surface imperfections diameter between and across the ribs weight and straightness length is checked in assembly with the uranium blanket pieces hollow spacer and spring and the parts are stored ready for loading into the Zircaloy fuel to this Zircaloy tube is attached to the hood through a vinyl pouch which completely covers the tip of the fuel to a funnel prevents external contamination as the fuel slugs enter the pouch remains sealed until the fuel tube is connected and ready for loading when loading is complete the pouch is dialectically sealed and cut off this closes the hood and seals a helium atmosphere around the open end during transfer to another hood for welding and filling with nak a connector is machine to provide the proper internal clearance and welded to the loaded fuel tube by a helium shielded tungsten arc as the tube is slowly rotated extreme care is exercised to prevent contamination of the weld joint and possible spread of contamination throughout the hood by volatilization of contaminants in the arc after checking the weld and alignment the tubes must be filled with the nak eutectic and the nak must be forced into the annulus between the slugs and the tube wall the rod is connected to a vacuum line while the lower end of the rod is rested upon a 60 cycle vibrator and a 5 micron vacuum drawn on the chamber a quantity of nak is injected and the rod is quickly brought to pressure to force the nak into the annulus the rod is deliberately overfilled and then brought to the proper level with a second hypodermic needle finally the filling hole is sealed by a Zircaloy plug a 700 watt second discharge fuses the plug and coupler top into a spherical weld bead the fuel rods are transferred to a clean air atmosphere hood where they are checked for contamination they are passed between alpha probes while slowly rotated and if contaminated they are cleaned in an ultrasonic scrubbing tank the clean rods are removed from the line for final testing welds are checked for leaks by sealing the top of the element into a small chamber the chamber is pressurized with a metered volume of helium and any decay in the pressure of this chamber is detected and recorded a previous heat treatment was performed to establish wetting between the nak plutonium and zirconium surfaces this bond is verified by eddy current probes and the finished rods are x-rayed the position of components and the nak level within the hollow spacer are readily verified throughout the production line fabrication procedures are carefully analyzed to achieve maximum control of nuclear radiation fire and personal safety hazards lutonium is exposed only in the filtered recirculating helium atmosphere under a slightly negative pressure standard criticality procedures are observed the fuel is handled with tools and sharp projections which could damage the gloves are avoided entrance or exit from the line is accomplished through multiple airlocks and seal bags although the EBR one mark for fuel is experimental in nature the handling techniques and precautions shown here are generally applicable to plutonium fabrication you

Channel: Nuclear Engineering at Argonne

Views: 10,067

Rating: 4.941606 out of 5

Keywords: nuclear, reactor

Id: RwHAQSKub7A

Length: 10min 8sec (608 seconds)

Published: Fri May 04 2018