International Assessments Program Overview
The Nuclear Fuel Cycle
Mary Beth Ward International Assessments Division Lawrence Livermore National Laboratory September 9, 2004 UCRL-PRES-203420
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract no. W-7405-Eng-48. CRS 9/7/2004 # 1
Key Points about the Nuclear Fuel Cycle • Definition: the set of processes to obtain, refine, and exploit nuclear material for a specific purpose, e.g. – Nuclear power – Production of fissile material for weapons – Nuclear propulsion
• Specific facilities and technologies should be chosen to support a specific purpose – A mismatch suggests the true purpose is different from the stated purpose
Nuclear fuel cycle for U.S. nuclear power plants
Nuclear Weapons Fuel Cycle •Goal is to produce fissile material for use in weapons – Also called “special nuclear material” or “special fissionable material” •Two main choices: Plutonium (Pu) or highly enriched uranium (HEU) – These materials have a high propensity to “fission” which can be exploited to produce a runaway nuclear chain reaction •Fissile material production is typically the hardest step – And the most amenable to controls –The key challenges are uranium enrichment, reactor, and reprocessing
Highly Enriched Uranium (HEU) • “Natural” Uranium is 99.3% U-238 and 0.7% U-235 • Uranium enrichment raises the concentration of the fissile isotope U-235 – – – –
Low enriched uranium (LEU) is defined as less than 20 % U-235 HEU is defined as at least 20% U-235 Weapons grade Uranium (WGU) is considered > 90% Depleted uranium has less than 0.7 % U-235
• “HEU” is often used synonymously (but incorrectly) with “weapons grade uranium” • Uranium enrichment is very difficult, especially on a large scale – Must separate atoms that are chemically identical but have a very slightly different mass
Four methods of uranium enrichment have been used on a large scale, two others are considered viable • Gas Centrifuge: spin uranium hexafluoride gas • Gaseous Diffusion: force UF6 gas through a membrane
Gas Centrifuge Cascade
• Electromagnetic Isotope Separation (EMIS): accelerate uranium atoms in a magnetic field • Aerodynamic/Jet Nozzle: stationary wall centrifuge • Laser Methods: use laser to selectively excite U-235 atoms/molecules • Chemical Methods
Gaseous Diffusion Unit
Calutron (EMIS) Track
Gas Centrifuge Technology is Particularly Sensitive • Gas centrifuge plants to produce HEU for weapons have no unique signatures – Modest size – Low energy consumption
• Gas centrifuge plants can be easily reconfigured to adjust the enrichment level • Gas centrifuge technology has spread all over the world – A.Q. Khan is the most visible distributor
• Many countries have the capability to produce gas centrifuge equipment – Key components and manufacturing equipment are export controlled
• Most popular method worldwide for civil and military enrichment
Centrifuge Diagram
Civil vs. military uranium enrichment facilities • There are only limited applications for uranium enrichment – LEU used for reactor fuel in most nuclear power reactors, typically 3 – 5 % U235 – Most research reactors use LEU fuel (typically 19.9 % U-235) – Most naval reactors use HEU (Goal is long lifetime between refueling and rapid power increases) – Nuclear weapons use weapon-grade uranium (about 90 % U-235)
• But from a proliferation perspective – Current world market in enrichment is depressed (measured in separative work units or SWUs) – SWUS are currently quite cheap, and have been for years – There is no economic incentive for countries to develop an enrichment capability, especially if they have only a few nuclear power plants
Interest in uranium enrichment outside large, industrialized countries is often viewed with suspicion
Plutonium Production is a multi-step process • Plutonium is produced by irradiating uranium in a nuclear reactor – Neutron absorption and transmutation (twice) in U-238
• As the reactor operates, the concentration of plutonium builds up the fuel • After the fuel is withdrawn, the fuel must be reprocessed to extract the plutonium
Plutonium “button” (produced after reprocessing)
Civil vs. military reactors • A reactor built for plutonium production is called a production reactor – Proliferators typically call their production reactor a research reactor – Proliferators tend to prefer reactors that use natural uranium fuel – Most efficient plutonium production – Don’t need to buy or make enriched uranium – Such a reactor must use either “Heavy Water” or “Reactor grade graphite” as the moderator – A 40-MW reactor fueled with natural uranium will produce about 8 – 10 kg/yr plutonium, enough for 1 weapon/yr
• Most research reactors are not well suited to plutonium production – A “standard” research reactor (fueled with LEU, moderated with light water, up to 10 MW) does not produce enough plutonium in the fuel to be of proliferation concern – But could produce several kg/yr plutonium in “targets” – Such a reactor produces plenty of neutrons for research
Interest in natural uranium-fueled research reactors is generally viewed with suspicion, except in cases where a country has a nuclear power program that also uses natural uranium-fueled reactors
Reprocessing is an especially sensitive technology • “Reprocessing” is the chemical process to extract plutonium from spent fuel • It’s hard – The plutonium is at a low concentration in the fuel – The fuel is highly radioactive – There are lots of chemical species represented in the fission products • The industry standard process is called PUREX for “Plutonium Recovery by Extraction”
PUREX Chemical Flow Scheme
Reprocessing is essential for production of separated plutonium for weapons Reprocessing is done as part of a civil nuclear fuel cycle only in a few advanced countries, although many believe the future of nuclear power depends on more widespread civil reprocessing
Basic Nuclear Weapon Design • Goal is to assemble a “supercritical” system that will allow a runaway nuclear chain reaction – Energy comes from many many fission reactions taking place in a very short period of time
• There are two basic concepts: gun-assembled and implosion systems • Key steps include design, manufacture, and testing
Fabrication
Non-nuclear (high explosive) testing
Nuclear Testing
Nuclear Fission Fission is the nuclear reaction that splits the atom, producing neutrons and energy
36 Kr
90
n n
92U
235 236* U 92 143 56 Ba
n n
Chain Reactions Neutrons produced in the fission reaction can go on to cause more fissions
Goal is to assemble a critical mass that will allow a runaway nuclear chair reaction
etc.
A system that will sustain a runaway fission chain reaction is called “supercritical”
Fission Weapons: Gun Type Assembly Goal is to rapidly bring together two subcritical masses to achieve a prompt supercritical mass
“Little Boy” Gun-type weapon
Fission Weapons: Implosion Assembly
Goal is to compress a subcritical sphere of special nuclear material to form a prompt supercritical mass
“Fat Man” implosion weapon
Summary: There are many potential indicators of nuclear weapon development • Production of fissile material, or development of facilities that are well suited for this purpose – Uranium enrichment facility – Nuclear reactor well suited to plutonium production – Fuel reprocessing facility – This step is the most visible and most difficult and has the longest lead time, and is most amenable to controls • Nuclear weapon design and development – High explosive (non-nuclear testing) – Acquisition of special material, e.g. for a neutron initiator • Technical barriers to proliferation are continually being lowered – 1940s-era technology accessible to more and more countries – More “secrets” of sensitive technology being revealed – Precision manufacturing and materials technologies spreading worldwide
Mary Beth Ward International Assessments Division Lawrence Livermore National Laboratory September 9, 2004 UCRL-PRES-203420
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract no. W-7405-Eng-48. CRS 9/7/2004 # 1
Key Points about the Nuclear Fuel Cycle • Definition: the set of processes to obtain, refine, and exploit nuclear material for a specific purpose, e.g. – Nuclear power – Production of fissile material for weapons – Nuclear propulsion
• Specific facilities and technologies should be chosen to support a specific purpose – A mismatch suggests the true purpose is different from the stated purpose
Nuclear fuel cycle for U.S. nuclear power plants
Nuclear Weapons Fuel Cycle •Goal is to produce fissile material for use in weapons – Also called “special nuclear material” or “special fissionable material” •Two main choices: Plutonium (Pu) or highly enriched uranium (HEU) – These materials have a high propensity to “fission” which can be exploited to produce a runaway nuclear chain reaction •Fissile material production is typically the hardest step – And the most amenable to controls –The key challenges are uranium enrichment, reactor, and reprocessing
Highly Enriched Uranium (HEU) • “Natural” Uranium is 99.3% U-238 and 0.7% U-235 • Uranium enrichment raises the concentration of the fissile isotope U-235 – – – –
Low enriched uranium (LEU) is defined as less than 20 % U-235 HEU is defined as at least 20% U-235 Weapons grade Uranium (WGU) is considered > 90% Depleted uranium has less than 0.7 % U-235
• “HEU” is often used synonymously (but incorrectly) with “weapons grade uranium” • Uranium enrichment is very difficult, especially on a large scale – Must separate atoms that are chemically identical but have a very slightly different mass
Four methods of uranium enrichment have been used on a large scale, two others are considered viable • Gas Centrifuge: spin uranium hexafluoride gas • Gaseous Diffusion: force UF6 gas through a membrane
Gas Centrifuge Cascade
• Electromagnetic Isotope Separation (EMIS): accelerate uranium atoms in a magnetic field • Aerodynamic/Jet Nozzle: stationary wall centrifuge • Laser Methods: use laser to selectively excite U-235 atoms/molecules • Chemical Methods
Gaseous Diffusion Unit
Calutron (EMIS) Track
Gas Centrifuge Technology is Particularly Sensitive • Gas centrifuge plants to produce HEU for weapons have no unique signatures – Modest size – Low energy consumption
• Gas centrifuge plants can be easily reconfigured to adjust the enrichment level • Gas centrifuge technology has spread all over the world – A.Q. Khan is the most visible distributor
• Many countries have the capability to produce gas centrifuge equipment – Key components and manufacturing equipment are export controlled
• Most popular method worldwide for civil and military enrichment
Centrifuge Diagram
Civil vs. military uranium enrichment facilities • There are only limited applications for uranium enrichment – LEU used for reactor fuel in most nuclear power reactors, typically 3 – 5 % U235 – Most research reactors use LEU fuel (typically 19.9 % U-235) – Most naval reactors use HEU (Goal is long lifetime between refueling and rapid power increases) – Nuclear weapons use weapon-grade uranium (about 90 % U-235)
• But from a proliferation perspective – Current world market in enrichment is depressed (measured in separative work units or SWUs) – SWUS are currently quite cheap, and have been for years – There is no economic incentive for countries to develop an enrichment capability, especially if they have only a few nuclear power plants
Interest in uranium enrichment outside large, industrialized countries is often viewed with suspicion
Plutonium Production is a multi-step process • Plutonium is produced by irradiating uranium in a nuclear reactor – Neutron absorption and transmutation (twice) in U-238
• As the reactor operates, the concentration of plutonium builds up the fuel • After the fuel is withdrawn, the fuel must be reprocessed to extract the plutonium
Plutonium “button” (produced after reprocessing)
Civil vs. military reactors • A reactor built for plutonium production is called a production reactor – Proliferators typically call their production reactor a research reactor – Proliferators tend to prefer reactors that use natural uranium fuel – Most efficient plutonium production – Don’t need to buy or make enriched uranium – Such a reactor must use either “Heavy Water” or “Reactor grade graphite” as the moderator – A 40-MW reactor fueled with natural uranium will produce about 8 – 10 kg/yr plutonium, enough for 1 weapon/yr
• Most research reactors are not well suited to plutonium production – A “standard” research reactor (fueled with LEU, moderated with light water, up to 10 MW) does not produce enough plutonium in the fuel to be of proliferation concern – But could produce several kg/yr plutonium in “targets” – Such a reactor produces plenty of neutrons for research
Interest in natural uranium-fueled research reactors is generally viewed with suspicion, except in cases where a country has a nuclear power program that also uses natural uranium-fueled reactors
Reprocessing is an especially sensitive technology • “Reprocessing” is the chemical process to extract plutonium from spent fuel • It’s hard – The plutonium is at a low concentration in the fuel – The fuel is highly radioactive – There are lots of chemical species represented in the fission products • The industry standard process is called PUREX for “Plutonium Recovery by Extraction”
PUREX Chemical Flow Scheme
Reprocessing is essential for production of separated plutonium for weapons Reprocessing is done as part of a civil nuclear fuel cycle only in a few advanced countries, although many believe the future of nuclear power depends on more widespread civil reprocessing
Basic Nuclear Weapon Design • Goal is to assemble a “supercritical” system that will allow a runaway nuclear chain reaction – Energy comes from many many fission reactions taking place in a very short period of time
• There are two basic concepts: gun-assembled and implosion systems • Key steps include design, manufacture, and testing
Fabrication
Non-nuclear (high explosive) testing
Nuclear Testing
Nuclear Fission Fission is the nuclear reaction that splits the atom, producing neutrons and energy
36 Kr
90
n n
92U
235 236* U 92 143 56 Ba
n n
Chain Reactions Neutrons produced in the fission reaction can go on to cause more fissions
Goal is to assemble a critical mass that will allow a runaway nuclear chair reaction
etc.
A system that will sustain a runaway fission chain reaction is called “supercritical”
Fission Weapons: Gun Type Assembly Goal is to rapidly bring together two subcritical masses to achieve a prompt supercritical mass
“Little Boy” Gun-type weapon
Fission Weapons: Implosion Assembly
Goal is to compress a subcritical sphere of special nuclear material to form a prompt supercritical mass
“Fat Man” implosion weapon
Summary: There are many potential indicators of nuclear weapon development • Production of fissile material, or development of facilities that are well suited for this purpose – Uranium enrichment facility – Nuclear reactor well suited to plutonium production – Fuel reprocessing facility – This step is the most visible and most difficult and has the longest lead time, and is most amenable to controls • Nuclear weapon design and development – High explosive (non-nuclear testing) – Acquisition of special material, e.g. for a neutron initiator • Technical barriers to proliferation are continually being lowered – 1940s-era technology accessible to more and more countries – More “secrets” of sensitive technology being revealed – Precision manufacturing and materials technologies spreading worldwide
