PROLIFERATION RESISTANCE OF THE FUEL CYCLE,, FOR THE * *' • "' 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 and 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 and other 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 , 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 .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 -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 , 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 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, , 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 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. The normal electrolyte in the nonproliferation measures and accept international elee'crorefiner would have to be removed safeguards at some or all of their nuclear activities. and fresh electrolyte installed. Applicable safeguards documents depends on whether all nuclear activities are covered5 or apply only to 6 2. The PuCI3-to-UCI3 ratio in the specific activities and facilities- eleclrorefiner would have to be buiit up to about ten for preferential In practice, the International Atomic Energy electrotransport of plutonium by Agency (IAEA) seeks to emphasize materials processing many batches of blanket fuel accounting as a safeguards measure, but there is a and removing only uranium. A time of trend toward increased reliance on containment and six or seven weeks would be required. surveillance. For the IFR fuel cycle, containment and surveillance become a primary safeguards mechanism 3. Then plutonium product could be because acceptable material accountability may be produced. difficult to achieve in the IFR fuel cycle {see following section). Fortunately, the nature of the IFR fuel cycle Even if these measures were taken, the operations and of plants designed to accommodate the plutonium would still be contaminated with rare earths IFR fuel cycle gives confidence to the adequacy and and actinide elements and would still contain too much reliability of containment and surveillance. uranium to be regarded as suitable for fabrication into a . All operations are batch operations. Only solids in suitable containers are transported from one To produce weapons material of acceptable step to the next, or to storage through weighing or quality, a supplemental process, e.g., PUREX, would intermediate hold-up stations. Similarly, only solid be required. This would necessitate construction of materials are introduced or removed from the heavily new facilities. Such facilities probably could be more shielded, inert-atmosphere process cells through advantageously utilized to process core or blanket transfer locks designed to maintain the integrity of the material directly. The need to use a supplemental inert atmosphere. Plutonium removal would be difficult process to produce weapons-grade plutonium is strong because of the limited number of such locks. The high evidence of the proliferation resistance of the IFR fuel reactivity of IFR fissile materials, which will contain cycle. constituents that will produce high levels of , will require continued handling of such materials in shielded. insrt-atmosDhere containers. This situation should not only tend to Argonne is working vigorously to improve discourage unauthorized removal of fissile materials, materials accountability procedures. In particular, a but also make surveillance straightforward -- by, for method of determining fissile material input based on example, surveillance devices such as redundant, fission gas analysis by sampling (sniffing) the fuel independent radiation monitors, cameras, and other element plenum gas offers the possibility of giving a optical devices. The IAEA containment/surveillance total neutron fluence for each pin, from which the devices include the following: can be calculated very accurately. Various destructive and nondestructive analyses can be used to • Closed-circuit television, determine in-process inventories and product compositions. • Modular video systems for unattended surveillance, IV. CONCLUSIONS • Reactor power monitors, Regarding the proliferation resistance of the IFR • Ultrasonic seals, seal verifiers, cap metal fuel cycle, the following conclusions can be made: seals, paper seals, and thermal luminescent dosimeters, and 1. Plutonium would be very difficult to obtain from an IFR fuel cycle and, if obtained, could • Night vision devices, as appropriate. not be used with confidence to produce a nuclear weapon because of the high residual These, coupled with qualified inspectors, fission-product radioactivity level, the should produce an effective safeguards system. presence of significant quantities of heat- and neutron-producing isotopes, and the C. Materials Accountability. presence of significant amounts of uranium.

Even though the IFR fuel cycle has high 2. To date, no credible modifications of the resistance to because (a} the process have been conceived to improve the Plutonium product is unsuitable for nuclear weapons quality of the plutonium. To produce and requires either additional special processing or use acceptable plutonium for weapons of an alternative process such as PUREX, and (b) production, additional purification by a removal of plutonium-based material from the facility process such as PUREX would be required. would be exceedingly difficult with good surveillance This would also necessitate construction of procedures, materials accountability is an essential additional facilities. For production of feature of an effective nuclear safeguards program." weapons plutonium, complete substitution of This is needed to demonstrate that all input fissile the PUREX process for ihe IFR process material (plutonium) has been accounted for, and its might be advantageous. location is known. The 1991-1995 safeguards criteria issued by the IAEA include near real-time accountability 3. The best weapons-grade plutonium would be for reprocessing facilities.9 produced from blanket material, but, although this material would be purer than that produced from core material, additional This is a challenge for the IFf! fuel recovery processing by PUREX would still be process because of difficulty in establishing the amount necessary. of fissile material in the input fuel and in obtaining representative samples and accurate volume 4. Because material can be removed from the measurements. Fissile material output can 'be heavily shielded IFR fuel cycle facility only accurately determined by weighing and sampling through a limited number of transfer locks, products, and assessing the holdup in the electrorefiner surveillance to detect unauthorized removal by sampling the salt electrolyte and measuring its of such material should be very effective. volume. The fuel input measurement is currently based on reactor burn-up calculations. Random sampling of 5. Improvement in accountability of fissile batches of fuel-pin segments has also been considered, materials in the IFR fuel cycle is required. but there is confidence in neither. The IAEA does not Until and unless such improvement is currently recognize reactor burnup calculations as being achieved, containment/surveillance may be definitive as a method of accountability. the primary means of ensuring adequate safeguards. 6. Following abrogation of the nonproliferation "The Structure and Content of Agreements treaty, an offending state would need at least between the Agency and States Required in seven weeks to produce any plutonium Connection with the Treaty on the Nonproliferation product. of Nuclear Weapons," INCIRC-153 (corrected), International Atomic Energy Agency, Vienna, Austria (1972). V. REFERENCES

6. "The Agency's Safeguards System," L. BURRIS, "Spent Fuel from IFR is Renewed by INCIRC/66/Rev. 2, International Atomic Energy Electrarefining Process," Logos 7, No. 1, Argonne Agency, Vienna, Austria (1968). National Laboratory (Winter, 1989).

7. D. D. DHAYER, ed., "Equipment for Potential 2. Y. I. CHANG, "The Integral Fast Reactor," Nucl. Unattended Use in Treaty Verification Tech., 88, 129(1989). Applications," SAND90-0572, Sandia National Laboratories, (May 1990).

3. C. E. TILL and Y. I. CHANG, "Evolution of the 8. "Safeguards Cautions--1991-1995," Department of Liquid Metal Reactor: the Integral Fas! Reactor Safeguards, IAEA, Vienna, Austria (November (IFR) Concept," American Power Conference. 51, 1990). 688 (April 1989).

9. "International Fuel Cycle Evaluation," Vol. 9, 4. M. KRAT2ERT, "Nonproliferation Risks and International Atomic Energy Agency, Vienna, Benefits of the Integral Fast Reactor," IEAL-R/86- Austria (1990). 100, International Associates Limited, Fairfax, Virginia, December, 1986.