Fuel Reprocessing and Fuel Reprocessing and I t S ti M th d I t S ti M th d Isotope Separation Methods Isotope Separation Methods for ENU4930/6937: Elements of Nuclear Safeguards, Non for ENU4930/6937: Elements of Nuclear Safeguards, Non-Proliferation, and Security Proliferation, and Security Presented by Presented by Glenn E. Sjoden, Ph.D., P.E. Glenn E. Sjoden, Ph.D., P.E. Associate Professor and Associate Professor and FP&L Endowed Term Professor FP&L Endowed Term Professor -- -- 2007 2010 2007 2010 FP&L Endowed Term Professor FP&L Endowed Term Professor 2007.2010 2007.2010 Florida Institute of Nuclear Florida Institute of Nuclear Detection and Security Detection and Security Detection and Security Detection and Security Nuclear & Radiological Engineering Nuclear & Radiological Engineering University of Florida University of Florida
Transcript
Fuel Reprocessing and Fuel Reprocessing and I t S ti M th dI t S ti M th dIsotope Separation Methods Isotope Separation Methods
for ENU4930/6937: Elements of Nuclear Safeguards, Nonfor ENU4930/6937: Elements of Nuclear Safeguards, Non--Proliferation, and SecurityProliferation, and Security
Presented byPresented byyyGlenn E. Sjoden, Ph.D., P.E.Glenn E. Sjoden, Ph.D., P.E.
Associate Professor andAssociate Professor andFP&L Endowed Term ProfessorFP&L Endowed Term Professor ---- 2007 20102007 2010FP&L Endowed Term Professor FP&L Endowed Term Professor 2007.20102007.2010
Florida Institute of Nuclear Florida Institute of Nuclear Detection and SecurityDetection and SecurityDetection and SecurityDetection and Security
Nuclear & Radiological EngineeringNuclear & Radiological EngineeringUniversity of FloridaUniversity of Florida
OverviewOverview
– Introductioni i f i il i l h b– Discussion of Fissile Materials – French Pub
– Nuclear Fuel Cycle/• Front End / Back End
• Reactor Centric
C i– Conversion– Enrichment
R i– Reprocessing– Summary
Basic Power Reactor SchematicBasic Power Reactor Schematic
• Power is produced using nuclear fission to generate heat
• Neutrons are the fission chain carrier– Criticality is the precise balance of leakage,
absorption, production of neutrons (from fission) in a system called a “nuclear reactor”
– Subcritical/critical/supercritical– High power/Low power in reactors– Neutrons must be managed
From Benedict, et al, Nuc. Chem. Engineering
Discussion of Fissile Materials Discussion of Fissile Materials –– French PubFrench Pub
– Detailed Information on all fissile materialson all fissile materials
• Criticality potential• Critical Masses
B hi ld d– Bare, shielded
• Isotopic Nuclear Data
• Packaging limitations
The Nuclear Fuel Cycle: OverviewThe Nuclear Fuel Cycle: Overviewyy
• Front End vs Back End
• Centered around reactor irradiation
• Recovered materialRecovered material through reprocessing
• High level waste “conversion”• High level waste volume is <5% of fuel
conversion
From Reilly, et al, Passive NDA of Nuclear Materials, NRC Press, March 1991
The Nuclear Fuel Cycle: Step by StepThe Nuclear Fuel Cycle: Step by Stepy p y py p y p
• Application and use of uranium in different chemical and physical forms. As illustrated below, this cycle typically includes the following stages:typically includes the following stages:
• Uranium recovery to extract (or mine) uranium ore, and concentrate (or mill) the ore to produce "yellowcake"
• Conversion of yellowcake into uranium hexafluoride (UF6)(UF6)
• Enrichment to increase the concentration of uranium-235 (U235) in UF6
• Deconversion to reduce the hazards associated with the depleted uranium hexafluoride (DUF6), or “tailings,” p f ( ) gproduced in earlier stages of the fuel cycle
• Fuel fabrication to convert enriched UF6 into fuel for nuclear reactors
• Use of the fuel in reactors (nuclear power, research, or naval propulsion)
• Interim storage of spent nuclear fuel • Recycling (or reprocessing) of high-level waste
(currently not done in the U.S.)• Final disposition (disposal) of high-level waste
• Yellowcake is produced at the mill• Yellowcake converted into pure uranium hexafluoride (UF6) gas
– impurities are removed; uranium is combined with fluorine to create the UF6 gas.p ; g– UF6 is then pressurized and cooled to a liquid.– In liquid state UF6 is drained into 14-ton cylinders where it solidifies after cooling for
approximately five days. – The UF6 in the cylinder, now in the solid form, is then shipped to an enrichment plant
• UF6 is the only uranium compound that exists as a gas at a suitable temperature.• One example of a conversion plant is operating in the United States:
H ll I t ti l I i M t li Illi i– Honeywell International Inc. in Metropolis, Illinois. – Canada, France, United Kingdom, China, and Russia also have conversion plants.
• Primary risks associated with conversion are chemical and radiological. – Strong acids and alkalis are used in the conversion processStrong acids and alkalis are used in the conversion process– Converting the yellowcake (uranium oxide, U3O8 ) powder to very soluble forms, leading to
possible inhalation of uranium. – Conversion produces extremely corrosive chemicals that could cause chemical, fire and
• Most nuclear reactors need higher concentrations of U235 than found in natural uranium • U235 is "fissionable," meaning that it starts a nuclear reaction and keeps it going.
– Normally, the amount of the U235 isotope is enriched from 0.7% of the uranium mass to about 5%, as illustrated in this diagram of the enrichment process.
• The three processes often used to enrich uranium are – Gaseous diffusion (the only process currently in the United States for commercially
enrichment)enrichment)– Gas centrifuges (as often reported in Iran) and Becker Nozzle (South Africa)– AVLIS (Atomic Vapor Laser Isotope Separation)
• Enriching uranium increases proportion of uranium atoms that can be "split" by fission• Not all uranium atoms are the same.
– Mined uranium is typically 99.3% uranium-238 or U-238 (U238), 0.7% uranium-235 or U-235 (U235), < 0.01% uranium-234 or U-234 (U234).
• These are the different isotopes of uranium: U234, U235, U238– While they all contain 92 protons in the atom’s center, or nucleus (which is what makes it
uranium)uranium), – the U238 atoms contain 146 neutrons, the U235 atoms contain 143 neutrons, and the U234
atoms contain only 142 neutrons. – (The total number of protons plus neutrons gives the atomic mass of each isotope
• — that is, 238, 235, or 234, respectively.) • Under the Atomic Energy Act, as amended, NRC must license a uranium enrichment plant under
10 CFR Parts 40 (source material) and 70 (special nuclear material). – Before an applicant can begin construction of a plant, NRC must issue a license forBefore an applicant can begin construction of a plant, NRC must issue a license for
construction and operation. To issue a license, the NRC must prepare an Environmental Impact Statement (EIS) and a Safety Evaluation Report for the project. NRC must also conduct a formal hearing before issuing a license, and members of the public may request status as intervenors in order to raise important safety or environmental issues about the proposedintervenors in order to raise important safety or environmental issues about the proposed plant.
From USNRC, April 2010
Types of Enrichment: ElectromagneticTypes of Enrichment: Electromagneticyp gyp g• E-M Separation (“Calutron Method”) uses mass
spectrometry• Charged particles are deflected in a magnetic field• Charged particles are deflected in a magnetic field
• The amount of deflection depends upon the particle's mass
• The most expensive enrichment method for h i ( ) d dthe quantity (mass) produced
• Has an extremely low throughput• Enables very high purities to be achieved • Often used for processing small amounts ofOften used for processing small amounts of
pure isotopes for research or specific use (such as isotopic tracers)
• Impractical for industrial use based on throughout and costthroughout and cost
Historical fact: At Oak Ridge and University of California, Berkeley, Ernest O. Lawrence developed electromagnetic separation for much of the uranium used in the first United States atomic bomb (see Manhattan Project)
From USNRC and Wiki, April 2010
used in the first United States atomic bomb (see Manhattan Project). Devices using his principle are named calutrons.
Types of Enrichment: Gaseous DiffusionTypes of Enrichment: Gaseous Diffusion• Uranium Hexafluoride (UF6) gas slowly fed in plant’s pipelines • Pumped through special filters called barriers or porous membranes• UF6 gas strikes porous membrane (barrier)
• GD Process uses molecular diffusion to separate a gas• GD Process uses molecular diffusion to separate a gas • Holes in barriers are very small; just enough room for UF6 gas molecules to pass through • uses the different molecular velocities of the two isotopes from a two-gas mixture
• Enrichment occurs when the lighter UF6 gas molecules (with the U234 and U235 atoms) tend g g ( )to diffuse faster through the barriers than the heavier UF6 gas molecules containing U238
• One barrier isn’t enough, though. It takes many hundreds of barriers, one after the other, before the UF6 gas contains enough U235 to be used in reactors.
• At the end of the process enriched UF6 gas is withdrawn from the pipelines• At the end of the process, enriched UF6 gas is withdrawn from the pipelines– Condensed back into a liquid and poured into containers. – Allowed to cool and solidify before transport to fuel fabrication facilities
From USNRC, April 2010
Types of Enrichment: Gaseous DiffusionTypes of Enrichment: Gaseous Diffusion
Hazards: • The primary hazard in gaseous diffusion plants include the chemical and
radiological hazard of a UF6 release and the potential for mishandling the enriched uranium, which could create a criticality accident (an inadvertent
l h i i )nuclear chain reaction).• Plants:
– The only gaseous diffusion plant in operation in the United States is in Paducah, Kentucky. Portsmouth GDP in Piketon, Ohio, shut down in March 2001.
– Both plants are leased to the United States Enrichment Corporation (USEC) from the U.S. Department of Energy and have been regulated by the NRC since March 4, 1997
From USNRC, April 2010
Types of Enrichment: Gaseous DiffusionTypes of Enrichment: Gaseous Diffusion
K 25 GDP O k Rid TNK-25 GDP, Oak Ridge, TN From Benedict, et al, Nuc. Chem. Engineering
Types of Enrichment: Gaseous CentrifugeTypes of Enrichment: Gaseous Centrifugeyp gyp g• Gas Centrifuge uranium enrichment process
• Large collective of rotating cylinders containing UF6 gas are ganged in series and parallel formations
• Centrifuge machines are interconnected to form trains and cascades
• UF6 gas is placed in a cylinder and rotated at a high speed. Thi t ti t t t if l f• This rotation creates a strong centrifugal force
• Mass is conserved, but heavier gas molecules (containing U238) move toward the outside of the cylinder, and lighter gas molecules (containing U235) collect closer to the center
• The enriched and the depleted gases in each centrifuge are removed by scoops
• A stream slightly enriched in U235 is withdrawn and fed g yinto the next higher stage
• A slightly depleted stream is recycled back into the next lower stage.
• Significantly more U235 enrichment can be obtained from a
From USNRC, April 2010
• Significantly more U235 enrichment can be obtained from a single-unit gas centrifuge than from a single-unit gaseous diffusion stage.
Types of Enrichment: Gaseous CentrifugeTypes of Enrichment: Gaseous Centrifugeyp gyp g
• No gas centrifuge commercial production plants are currently operating in the United States.
• Louisiana Energy Services (LES) and USEC Inc. have recently received licenses to construct and operate commercial enrichment facilities.
• USEC Inc. was granted a license in February 2004 g yfor a demonstration and test gas centrifuge plant, which is currently under construction. Both of these commercial facilities are now under construction.
• December 30, 2008, AREVA Enrichment Services, LLC (a subsidiary of AREVA NC, Inc.), submitted an application to the NRC
• Seeking a license to construct and operate a gas• Seeking a license to construct and operate a gas centrifuge facility in Bonneville County, Idaho. This proposed plant is known as the Eagle Rock Enrichment Facility.
From USNRC, April 2010 From Benedict, et al, Nuc. Chem. Engineering
Types of Enrichment: Becker NozzleTypes of Enrichment: Becker Nozzleypyp
• Becker Nozzle Process was perfected in South Africa• A dilute mixture of (fmole fraction) UF6 in hydrogen at
upstream pressure p is expanded through a convergent-divergent slit with throat spacing s into curved groove of radius a.
• After being deflected through 180o by the wall of the g g ycurved groove, the gas stream at lower pressure p' traveling at high speed is separated by a flow divider set at radius c into an outer heavy fraction depleted in UF6 + hydrogen, and an inner light fraction enriched in these y g gcomponents.
• The separation factor “alpha” is higher the higher the speed attained by the gas, which is higher the higher the pressure ratio p/p' and the lower the UF6 content of thepressure ratio p/p and the lower the UF6 content of the feed gas
From Benedict, et al, Nuc. Chem. Engineering
Types of Enrichment: AVLISTypes of Enrichment: AVLISypyp• Atomic Vapor Laser Isotope Separation (AVLIS), Molecular Laser Isotope Separation (MLIS),
and Separation of Isotopes by Laser Excitation (SILEX) all inviolve isotopic separation of uranium based on photoexcitation principles p p p
• Exciting the molecules using laser light • Three major systems are required
• Laser system, Optical system, Separation module system• Tunable lasers can be developed to deliver monochromatic radiation (light of a single-color)
• The radiation from these lasers can photoionize a specific isotopic species while not affecting other isotopic species.
• The affected species is then physically or chemically changed, which enables the materialThe affected species is then physically or chemically changed, which enables the material to be separated.
• AVLIS used a uranium-iron (U-Fe) metal alloy as feed, while SILEX and MLIS use UF6• No laser separation uranium enrichment plants are currently operating in the United States.
• In 2007, General Electric - Hitachi submitted a license amendment request to the NRC, seeking approval for R&D associated with laser enrichment at GNF in Wilmington, NC.
• The NRC approved the amendment on May 12, 2008, and GE-Hitachi is currently constructing the test loop with the intention of beginning operations in the near future.
• June 2009, GE-Hitachi license application for commercial laser enrichment plant
• Light Water Reactor (LWR) Low-Enriched Uranium (LEU) FuelFuel
• Typically begins with receipt of low-enriched uranium (LEU) hexafluoride (UF6) from an enrichment plant.
• UF6 solid in cylinders is heated to gaseous form• UF6 gas is chemically processed to form LEU uranium
dioxide (UO2) powder• Powder is then pressed into pellets• Pellets are sintered into ceramic form and loaded intoPellets are sintered into ceramic form and loaded into
Zircaloy tubes• Tubes filled with pellets are constructed into fuel
assemblies. D di h f li h f l• Depending on the type of light water reactor, a fuel assembly may contain up to 264 fuel rods and have dimensions of 5 to 9 inches square by about 12 feet long.
From USNRC, April 2010
Fuel Cycle Facilities in the US by NRC RegionFuel Cycle Facilities in the US by NRC Regiony y gy y g
From USNRC, April 2010
Irradiated or “Used” FuelIrradiated or “Used” Fuel• Irradiated fuel is highly radioactive• “Burnup” in MW*Days/MT(hm)• Typical 33,000 MWD/MtuTypical 33,000 MWD/Mtu• When spent fuel is discharged, it
contains substantial amounts of fissile and fertile materialB f th fi i d t t• Because of the fission products, spent fuel is intensely radioactive --Activities of 10 Ci/g are common.
– 1 Ci is 3.7E10 dis/s
S f l i ll h ld i l d• Spent fuel is usually held in cooled storage basins (Spent Fuel Pools) at the reactor site for 150 days or more to allow some of the radioactivity to ddecay.
• If to be reprocessed, spent fuel would be shipped in cooled, heavily shielded casks, strong enough to remain intact in a shipping accident.
From Reilly, et al, Passive NDA of Nuclear Materials, NRC Press, March 1991
Reprocessing of “Used Fuel”Reprocessing of “Used Fuel”p gp g
Nuclear fuel reprocessing -the recovery and separationthe recovery and separation of fissile fuel, actinides, and fission products from fuel burned in a reactor
Reprocessing is essential to provide a stable nuclear fuel supply to meet current and pp yfuture energy demands, while minimizing spent-fuel waste streams and the associated need for high
PUREX Plant in Hanford, WA
associated need for high level waste storage facilities.
From Benedict, et al, Nuc. Chem. Engineering
ReprocessingReprocessing• Need to extract Pu for weapons drove development as part of Manhattan Project• Reprocessing separates components of spent nuclear fuel
– Recycling all actinides for reactor fuel– Closes the nuclear fuel cycle– Multiplies the energy extracted from natural uranium by more than 60
• Many processes investigated around WWII– PUREX process most efficient and produces separated plutonium that was usedPUREX process most efficient and produces separated plutonium that was used
for nuclear weapons• October 1976: Proliferation fears • President Gerald Ford to issue a Presidential directive to indefinitely suspend the
fcommercial reprocessing and recycling of plutonium in the U.S. • April 1977: President Jimmy Carter banned the reprocessing of commercial reactor
spent nuclear fuel– President Reagan lifted the ban in 1981, but did not provide the substantial g , p
subsidy that would have been necessary to start up commercial reprocessing.• March 1999: DOE reversed its own policy and signed a contract with a consortium of
Duke Energy, COGEMA, and Stone & Webster (DCS) to design and operate a Mixed Oxide (MOX) fuel fabrication facility Site preparation at the Savannah River SiteOxide (MOX) fuel fabrication facility. Site preparation at the Savannah River Site (South Carolina) began in October 2005.
From Multiple Sources: NCE, Reilly, Wiki
General Closed Fuel CycleGeneral Closed Fuel Cycle
From Benedict, et al, Nuc. Chem. Engineering
PUREXPUREX
• PUREX (Plutonium URaniumEXtraction) aqueous processEXtraction) aqueous process flowsheet
• Reprocessing of nuclear fuel involves several distinct processes, including i t ti l t t tiisotope separation, solvent extraction, as well as the separation and purification of intensely radioactive fission products and materials.
• The organic solvent used is typically up to 30% tri-butyl phosphate (TBP) mixed with kerosene.
From Benedict, et al, Nuc. Chem. Engineering
• Extraction takes place in banks of centrifugal contactors or pulsed columns. p g p• PUREX is an excellent process when it comes to delivering separated uranium and
plutonium from spent fuel; however, it results in a direct separation of plutonium [Long]. • Under GNEP, proliferation resistance was viewed as pervasive and reprocessing
operations must actively prevent explicit separation of plutonium to avoid its diversion tooperations must actively prevent explicit separation of plutonium to avoid its diversion to weapons by state and non-state actors.
CETE UREX Demonstration at ORNLCETE UREX Demonstration at ORNL
From UT-Battelle, ORNL
• UREX process enables reprocessing without direct separation of Pu• Offers a pathway for proliferation resistance
UREX+1a UREX+1a FlowsheetFlowsheet• UREX+1a flowsheet—UREX is a new solvent extraction reprocessing method under development as part of the DOE R&D ; it has never been developed beyond the laboratory experimental scale
• Existing models assume ideal operation conditions not duplicated in practice, and there are deviations in the predictions from experimental data thoseand there are deviations in the predictions from experimental data--those involving dilute and/or multiple species.• The head end of UREX+1a begins with spent power fuel in cooling ponds. • Following years of cooled storage, and pre-processing via mechanical de-cladding operations, burned oxide fuel rods are dissolved in nitric acid. • The dissolved fuel is then contacted with a series of solvents that sequentially
t t k t t l d i l t th f th i iextract key components to complex and isolate them from the remaining mixture…
• The UREX (left) process is a modified PUREX process (above) where Pu is prevented from extraction. • This can be done by adding a plutonium reductant before the first metal extraction step. • In the UREX process, ~99.9% of the Uranium and >95% of Technetium are separated from each other and other fission products & actinides. • The key is the addition of acetohydroxamic acid (AHA) to the extraction and scrub sections of the process. Use of AHA greatly diminishes the extractability of Pu and Np, providing
From UT-Battelle, ORNL
the extractability of Pu and Np, providing greater proliferation resistance than with the plutonium extraction stage of the PUREX process.
SummarySummary
Fuel Cycle and related Enrichment and Fuel Cycle and related Enrichment and Reprocessing are complex subjectsReprocessing are complex subjectsWe touched on each here in a brief overviewWe touched on each here in a brief overviewMore on these will be covered in exercises through More on these will be covered in exercises through thththe coursethe course
