The Fabrication of Plutonium from Highly Irradiated Reactor Fuel

Plutonium that has been separated from highly irradiated, or recycled, reactor fuel contains substantial percentages of 238Pu, 240 Pu, 241Pu and 242Pu. These isotopes and their daughter products are sources of increased gamma and neutron radiation, which affects the costs, the facilities and the techniques of fabricating the plutonium into reactor fuel elements. The commercial application of recycled power-reactor plutonium will depend, to a large extent, upon the ability of the fabricators to process, fabricate and use plutonium derived from highly irradiated fuels economically and safely. Experimental fuel elements are being fabricated at Argonne National Laboratory for a long-range study of the effects on reactor neutronics of various plutonium isotopic compositions that range from nearly pure 239Pu to plutonium that is principally 242Pu. A secondary purpose of this work was to determine the gamma and neutron rates of radiation dosage to personnel and to gain practical experience during the fabrication of typical compositions of plutonium from power reactors. The first step in this study was to develop a computer programme for calculating the rates of radiation dosage to personnel encountered during the fabrication of plutonium metal fuel elements of any isotopic composition versus time after fabrication. The effects of mass, geometry, shield composition and thickness, and time of operator exposure may be factored into the programme and the total operator radiation exposure predicted. The second stage was to compare the calculated exposures with measured radiation exposures during the fabrication of plutonium metal and oxide fuel elements containing 10, 30 and 50% of the higher plutonium isotopes. The fabrication of 2-kg batches of plutonium was accomplished unshielded gloveboxes with lightly leaded gloves. Glove-hand contact with the plutonium was avoided, and the operator time spent at the glovebox face was limited. The weekly exposure of each operator to radiation was kept below 100 mrem. The final step of the study was the extrapolation of the calculations and experience to reactor-scale fuel fabrication to predict whether glovebox, semiremote, or remote fabrication will be required. The following conclusions have been reached from this study: (1) Unshielded glovebox fabrication is practical for intermittent, small-scale fabrication of almost any plutonium composition, provided that the work is preplanned, the plutonium is fabricated soon after separation, exposures to personnel are monitored, and operators are rotated before they are overexposed to radiation. (2) Multikilogram quantities of plutonium, containing 30 to 50% of the higher plutonium isotopes, can be fabricated in shielded gloveboxes with leaded gloves and with the precautions listed in (1). Gloved-hand contact with the plutonium should be avoided to prevent overexposure to gamma and neutron radiation. (3) Personnel rotation would become too frequent in many operations for the glovebox fabrication of recycled power reactor fuel on a large scale, and semi-remote controlled fabrication will probably become necessary for the economic refabrication of the fuel. (author)