PROLIFERATION RESISTANCE OF THE FUEL CYCLE,, FOR THE INTEGRAL FAST REACTOR* *' • "' 30 833 Leslie Burris Argonne National Laboratory OSTI Chemical Technology Division 9700 South Cass Avenue Argonne, Illinois 60439 To be presented at GLOBAL '93 International Conference on Future Nuclear Systems: Emerging Fuel Cycles and Waste Disposal Options September 12-17,1993 Seattle, WA The submitted manuscript has been authored by a contractor of the U. S- Government under contract No. W-3M09-ENG-38. Accordingly, tht U. S. Government retains a nonexclusive, royaity-free ticente to publish or reproduce the published form of this contribution, or allow others to do to, for U. S. Government purposes. *Work supported by the U.S. Department of Energy, Nuclear Energy Research and Development Program, under Contract W-31-109-Eng-38. PH3TRIBUTION OP THIS DOOUMENT IS UNLIMITED t PROLIFERATION RESISTANCE OF THE FUEL CYC! P FOR THE INTEGRAL FAST REACTOR Leslie Burn's Argonne National Laboratory Chemical Technology Division 9700 South Cass Avenue Argonne, Illinois 60439 ABSTRACT discharged fuel. Yielding only partially decontaminated uranium and plutonium products, it promises high Argonne National Laboratory has developed an resistance to clandestine diversion or overt, state- electrorefining pyrochemical process for recovery and supported diversion of plutonium for production of recycle of metal fuel discharged from the Integral Fast nuclear weapons. Reactor (IFR).' This inherently low decontamination process has an overall decontamination factor of only In 1986, a study of the proliferation risks of a about 100 for the plutonium metal product. As a result, similar pyrochemical process for discharged IFR fuel atl of the fuel cycle operations must be conducted in was conducted by International Energy Associates heavily shielded cells containing a high-purity argon Limited.3 The conclusion was that "Overall, there is no atmosphere. The IFR fuel cycfe possesses high valid basis for concern that the development and resistance to clandestine diversion or overt, state- demonstration of the IFR will be prejudicial to U.S. supported removal of plutonium for nuclear weapons nonproliferation interests, and considerable basis for production because of two main factors: the highly the conclusion that it could offer modest radioactive product, which is also contaminated with nonproltferation gains...". heat- and neutron-producing isotopes of plutonium and other actinide elements, and the difficulty of removing An assessment of the proliferation potential and material from the IFR facility through the limited number international implications of the Integral Fast Reacts; of cell transfer locks without detection. and current IFR fuel cycles was conducted in 199! for DOE by a panel of highly experienced experts in fuel I. INTRODUCTION cycle and actinide chemistry, nuclear safeguards, and nuclear and nonproliferation foreign policy. The report The Integral Fast Reactor (IFR) is an advanced is classified and so is not referenced. The conclusions reactor concept that could help to meet the increasing in this paper are consistent with those of the DOE world demands for electrical power by making available panel. a huge new energy source-the uranium-238 isotope, which constitutes 99.3% of natural uranium.2-3 Only II. THE IFR FUEL CYCLE fast reactors can utilize the U-238 isotope, which is converted to plutonium-239, the fissionable isotope for The IFR fuel cycle is shown in Fig. 1. The fueling fast nuclear reactors. Argonne National principal steps are the following: Laboratory has been developing the IFR since about 1983. 1. Preparation of discharged fuel for processing. The IFR is a sodium-cooled, metal-fueled reactor. The fuel is a 70 w/o U-20 w/o Pu-tO w/o Zr alloy. Very 2. Processing by electrorefining. high fuel burnups, up to 20% of the heavy atoms, have been demonstrated in the Experimental Breeder 3. Vaporization of solvent metals and salts from Reactor (EBR) II, located near Idaho Falls, Idaho. electrorefiner products to yield a plutonium- rich U-Pu alloy and uranium metal. Because of the high plutonium concentration in the fuel, the IFR fuel cycle must be closed, that is, 4. Injection casting to produce new fuel pins, discharged fuel must be processed to recover the which are sheathed in thin-wall, type HT-9 fissionable and fertile elements for fabrication into new territic stainless steel cladding. The fuel elements for return to the reactor. An electro- sheathed pins are called fuel elements. refining process has been developed for processing the Fig. 1. The !FR Fuel Cell 5. Incorporation of fuel elements into fuel decontamination process. The overall decontamination assemblies for return to the reactor. factor for tfie plutonium product is expected to be limited to about 100, due principally to low separation These steps are discussed briefly below. of rare earth fission products, in addition, the other actinide elements, (americium, curium, and neptunium), A. Preparation of Discharged Fuel for accompany plutonium through the process and are Processing. recycled to the electforefiner, where they, too, are burned. These elements produce high levels of heat The enrj fittings on a fuel subassambly are and neutrons. cut off, after which the external wrapper tube is slit and opened to allow access to the fuel elements. The fuel C. Injection Casting. elements are chopped into 7«-in. (0.6-cm) long segments, which are loaded into an anode basket for The piutonium and uranium products from the charging into the electrorefiner. cathode processor, as well as zirconium alloying element are added to an injection casting crucible in 8. Electroreiining. amounts necessary to produce fuel of the desired composition. They are fused, and for injection casting, A schematic representation of an the temperature of the melt is raised to about 1400°C. electrorefiner is shown in Fig. 2. In the etectrorefming The crucible (graphite coated with yttria) is contained process, uranium and plutonium are eieetrotransported within a teak-tight bell jar furnace. Suspended above from She anode basket of fuel segments through a LiCt- the crucible is an array of open-ended molds {currenBy KCl electrolyte to their respective cathodes. Piutonium made of Vycor, but other materials are under together with some uranium is deposited in a liquid consideration). For injection casting, the furnace is cadmium cathode. The plutonium-to-uraniurn ratio in evacuated, and, as the array of tubes is quickly lowered the cadmium deposit is about 3 or 4 to 1. Uranium is into the meft, the furnace is pressurized, forcing the deposited as a bushy, dendritic crystal mass on a molten fue! into the molds where U quickly solidifies. round steel cathode mandrel. Adhering electrolyte salt The molds are subsequently broken away, and the pins on the uranium deposit and cadmium and electrolyte are cut to length for incorporation into fuel elements. salt accompanying the plutonium deposit are subsequently vaporized at high temperature and D. Fuel Assembly. reduced pressure in a unit called the cathode Fig. 2. Schematic of Electrorehner E. Fuel Cycle Facility. material being recycled; the nature of the fuel cycle, i.e., the fuel recovery and fabrication processes The IFR fuel cycle is to be demonstrated in employed in the fuel cycle facility; surveillance methods a facility adjacent to EBR-II (see Fig. 3). All operations and procedures; and materials accounting. Institutional must be conducted remotely behind 5 feet (1.5 m) of factors include the effectiveness of plant security and concrete shielding. Some operations, such as the frequency and thoroughness of safeguands dismantling of fuel subassemblies and fabrication of inspections. This paper deals with the technical new ones, are done in an air atmosphere cell. factors. Operations in which fuel is exposed are done in a high- integrity argon-atmosphere cell. Openings into these A. Proliferation Resistance Afforded by the cells for introduction or removal of fuel assemblies or Electrorefining Process. for removal of samples are limited in number. Any fuel material that is removed must be in shielded Much of the high proliferation resistance of containers. the IFR fuel cycle can be attributed to the electrorefining recovery process. The plutonium Full-size processing plants would have these product is unavoidably contaminated with rare earth same features. fission products-trie decontamination factor for rare earths ranges between five and ten, and with essentially all of aclinide elements (americium, curium, 111. PROLIFERATION RESISTANCE and neptunium) in the fuel charge, and with a substantial amount of uranium. The high rare earth For a fuel cycle to be proliferation resistant, concentrations in the plutonium produce such a high surreptitious removal of fissile material must be very radiation background (100 Rmr at 3 ft or 0.9 m) that the difficult and, if such removal is attempted, readily subsequent fabrication of fuel elements and assembly detectable. In the case of overt diversion of fissile of them into new fuel subassemblies must be material for weapons production by. ior instance, a conducted remotely. Because the chemical stabilities state violating the nonproliferation treaty (NPT), the of the chlorides of plutonium, other actinide elements, time required to modify the process and, if necessary, and the rare earths are similar, no plausible method equipment in order to produce weapons-grade has been devised far increasing decontamination from plutonium is important. A long time, one month being rare earths or the actinide elements in the long, allows the rest of the world time to mobilize efforts electroreSning process. to r1ter.nirr?rte ororinotrnn of nuclear wenoons tju the Reactor and Fuel Cycie Facility fUtt ELEUEMT IFWCl-W AND FABRICATION ( HUGO1- £'<-- • Fig. 3. The IFR Fuel Cycle Facility at EBR-II Plutonium, by operating with a high PuCI3-to-UCI3 ratio 8. CONTAINMENT AND SURVEILLANCE in the electrolyte, but the steps required are laborious and, in the end, fruitless. To extract only blanket A central feature of the current Plutonium: nonproliferation regime is a network of bilateral and multilateral agreements by which states undertake 1.