Radiochemistry Webinars

Transcription

1 National Analytical Management Program (NAMP) U.S. Department of Energy Carlsbad Field Office Radiochemistry Webinars Nuclear Fuel Cycle Series Introduction to the Nuclear Fuel Cycle In Cooperation with our University Partners

2 2 Meet the Presenter Dr. Stéphanie Cornet Dr. Stéphanie Cornet is a Nuclear Scientist at the OECD Nuclear Energy Agency in Paris, France, currently working in the area of Scientific Issues of the Nuclear Fuel Cycle. Dr. Cornet received the French equivalent of a master s degree in Chemistry from the University of Franche-Comté, and then moved to the United Kingdom to complete her doctoral studies in Inorganic Chemistry at the University of Durham. After a first postdoctoral position at the University of Montreal working on catalysis, Dr. Cornet spent 4 years as Postdoctoral Research Associate in the Centre for Radiochemistry Research at the University of Manchester (UK), where she was first introduced to nuclear science. Through the European network ACTINET, she had the opportunity to participate in a 6-month assignment at the CEA Marcoule Nuclear Site in France, where she worked on the preparation of plutonium complexes. She then obtained a position as a Teaching Fellow at the University of Manchester, where she taught the basics of the nuclear fuel cycle, as well as chemistry of the actinides. She gained extensive experience in the area of nuclear and radiochemistry, in particular the chemistry of actinide and transactinide elements in aqueous and non-aqueous media. Her research interests lie in the area of coordination chemistry of the f-elements, especially the chemistry of the actinides. She is particularly focused on anhydrous actinyl ({AnO2}2+) coordination chemistry and probing the actinyl bond along the actinide series (U, Np, Pu) to advance understanding of the electronic structure of actinyl complexes. Dr. Cornet is recognized for her expertise in non-aqueous transuranics.

3 3 Introduction to the Nuclear Fuel Cycle Dr. Stéphanie Cornet Nuclear Scientist, OECD Nuclear Energy Agency Paris, France National Analytical Management Program (NAMP) U.S. Department of Energy Carlsbad Field Office TRAINING AND EDUCATION SUBCOMMITTEE

4 4 Learning Objectives Understand the concepts of the nuclear fuel cycle Understand the difference between open and closed fuel cycle Learn the different processes involved in each stage of the fuel cycle

5 5 Outline What is the nuclear fuel cycle? Different stages of the fuel cycle Front-end: mining, enrichment, fuel fabrication Back-end: reprocessing, spent fuel storage and management, waste management Open vs closed fuel cycle Advanced fuel cycles and related advanced technologies

6 6 What is the Nuclear Fuel Cycle? Definition: The various activities associated with the production of electricity from nuclear reactors are referred to collectively as the nuclear fuel cycle These activities vary from country to country

7 7 What is the Nuclear Fuel Cycle? Energy is generated through a reaction called nuclear fission of fissile material Different types of fuel cycle: Uranium Fuel Cycle: 235 U is used as fissile material Uranium-Plutonium Fuel Cycle: Natural or depleted uranium including Pu to ensure chain reaction Thorium Fuel Cycle: 232 Th is fertile so fissile 235 U or 233 U is used as fissile material Most fuel cycles use fission of 235 U to produce electricity Nuclear Fission

8 8 The Nuclear Fuel Cycle What is it? Very important concept Industrial scales of inputs, processes and outputs Not necessarily a cycle Inputs: Uranium ore Process chemicals Fabrication materials Outputs: Energy Plutonium Waste Processes: Conversion & enrichment Fuel fabrication Power generation Reprocessing Waste treatment

9 9 The Nuclear Fuel Cycle The fuel cycle is commonly divided into front-end and back-end A fuel cycle can be open or closed

10 The Front-End of the Fuel Cycle 10

11 11 Front-end The aim of the front-end is to fabricate nuclear fuel Uranium ore mining and milling Uranium conversion Uranium enrichment to 235 U Reactor Fuel fabrication

12 12 Mining and Milling Uranium Average crustal abundance 2-5 ppm, Z=92 M Half Life (a, g decay) Fraction (3) x 10 9 y (10) (1) x 10 8 y (6) (6) x 10 5 y (5) Extraction by milling and chemical leaching Output is uranium ore concentrate (yellowcake) Image source: Areva Tailings image from info/ Warning: not to be confused with yellow cake

13 13 Conversion and Enrichment Convert yellowcake to UF 6 -purification Only 235 U is fissile (0.711% abundance) Generally enrich to ~3wt% in fuel Gaseous diffusion or centrifuge of UF 6 Image source: Urenco, Ltd.

14 14 Conversion From U 3 O 8 yellowcake (~80% U) to UF 6 gas Use of fluorine: - Only one isotope - Commercially viable - Purity: UF 6 is the only uranium compound that is a gas at room temperature

15 15 Enrichment 0.7 % 235 U in natural U % 235 U for PWR Two main enrichment technologies (operating at commercial scale): Gaseous diffusion Gas centrifuge Other techniques exist, but are less developed (e.g., laser enrichment) Image source: and NRC

16 16 Fuel Fabrication Enriched 235 UF 6 is converted to UO 2 UO 2 made into pellets (sintering and pressing) Pellets loaded into fuel pins Pins bundled to make assemblies Image sources:

17 17 Power Generation Fuel loaded in reactor (for 2-4 years) Fission of 235 U=FPs+2.5n+energy Moderation-thermal neutrons Coolant, steam cycle and generator Spent fuel cooled for 4-6 years Images from CEA

18 18 The Reactor Three basics components: Fuel: Fissile material necessary to maintain chain reaction Moderator: Reduces neutron energy to enhance fission probability Light material, non-absorbing Water, graphite Coolant: Removes heat generated in the fuel Carries the heat for conversion Light Water Reactors (LWRs) represent the majority of reactors operating in the world today Image from CEA Clefs no. 46 (2002)

19 The Back-End of the Fuel Cycle 19

20 20 Back-end The aim of the back-end is the treatment of spent nuclear fuel Reactor At-reactor storage Away from reactor storage SNF reprocessing Geological disposal

21 21 Spent Nuclear Fuel Storage Spent nuclear fuel (SNF) Highly radioactive, large decay heat Stored in pools for cooling and shielding (minimum 2 to 3 years) Long-term storage (interim storage) SNF shipped in casks to dry cask storage Images from NRC

22 22 Reprocessing Reprocessing/Recycling Recovery of fissile material to reuse for fabrication of new fuel Separation of nuclear waste Spent fuel is approximately: 96% U, 1% Pu, 3% FP+MA Fissile U and Pu are valuable Recover by dissolution and reprocessing Fuel dissolution and solvent extraction Images from AREVA

23 23 Reprocessing Characteristic of fuel irradiated on a LWR U: 96% Pu: 1% FP/MA: 3% Images from AREVA

24 24 Reprocessing The PUREX (Pu and U Recovery by Extraction) process (aqueous process) 1- decladding and chopping 2- dissolution in HNO3 3- extraction of U and Pu with Tri-n-butyl phosphate (TBP) 4- Pu recovery from TBP organic phase Only a few reprocessing plants in the world (France, UK, Russian Fed., Japan, India and China) Images from and AREVA

25 25 Waste Management Spent nuclear fuel and waste SNF must be suitably packaged for disposal Wastes from reprocessing must be immobilized Classify wastes depending on activity and heat (IAEA classification but varies according to countries) No high-activity disposal facility yet in operation Images from Diagram of the facilities at CIGEO, France

26 26 Conditioning and Immobilization Treatment and conditioning Convert waste into suitable form: Minimize volume Reduce hazard Immobilization Stable solid waste to prevent dispersion Cementation (ILW) or vitrification (HLW) Images from WNA and AREVA

27 27 Geological Disposal What is a nuclear geological repository? Engineered facility deep below the ground Uses the waste form, the waste package, specially designed engineered seals and stable geology to ensure safety Provides a high level of long-term isolation and containment No retrieval of wastes 13 countries currently pursuing geological disposal for a variety of waste types

28 28 Open vs Closed Fuel Cycle A different way of managing used fuel Open or once-through fuel cycle Spent fuel discharged from the reactor is treated as waste Fuel is kept in at-reactor pool Waste in interim storage before being disposed of in geological disposal The U.S. has adopted an open fuel cycle, as other countries Image from DOE

29 29 Open vs Closed Fuel Cycle Closed Fuel Cycle (= recycling) Spent fuel reprocessed to extract U and Pu from FPs and other actinides Reuse of recovered fissile U in UOX or MOX Use of Pu in MOX fuel Burn MOX in LWR or FR France, for example, has adopted a closed fuel cycle

30 30 Open vs Closed Fuel Cycle Today s closed fuel cycle Reuse U/Pu in LWR as MOX fuel Recycle only once Partial recycle Closed fuel cycle Future fuel cycle Pu is reused to make fuel for FR and SNF from FR is reused in FR Choice of NFC (open, closed, or partially closed) depends on The features of proven technology options Societal weighting of goals (economics, safety, waste management, and non-proliferation) With today s knowledge about future options and goals, it is difficult to make definite choices

31 31 Why Close the Fuel Cycle? Source of energy Residual fissile materials can be recycled as new fuel Resource conservation Repository and waste management Superior storage and disposal forms relative to SNF Separate transuranic (TRU or actinides) for transmutation Non-proliferation objectives Avoid sending fissile materials to repository or long-term storage

32 Alternative Fuel Cycles 32

33 33 Advanced Fuel Cycles Safe, secure, economical and sustainable expansion of nuclear energy Minimize waste and environmental impact Enhance safety and proliferation resistance towards closing the NFC Nuclear energy systems of the future (e.g., fast reactors) Development of advanced and innovative technologies (e.g., partitioning and transmutation) Images from Gen IV forum

34 34 Advanced Nuclear Systems Definition (IAEA): Designs of current interest of which improvements over predecessors and/or existing designs is expected Image from Gen IV forum

35 35 Advanced Nuclear Systems Generation IV systems Systems VHTR (Very high-temperature reactor) SFR (Sodium-cooled fast reactor) SCWR (Supercritical water-cooled reactor) GFR (Gas-cooled fast reactor) LFR (Lead-cooled fast reactor) MSR (Molten salt reactor) Neutron Spectrum Coolant Outlet Temperature Fuel Cycle Size Thermal Helium Open Fast Sodium Closed Thermal/fast Water Open/closed Fast Helium 850 Closed 1200 Fast Lead Closed Thermal/fast Fluoride salts Closed 1000 Image from Gen IV forum

36 36 Advanced Nuclear Systems Small and medium size reactors (SMRs) Aims: provide increased benefits in areas of safety and security, non-proliferation, waste management, resource utilization and economy Interest mainly driven by desire to reduce impact of cost, shorter construction times Under development: deployment by Image from IAEA

37 37 Advanced and Innovative Technologies Innovative Fuels (Transmutation) Better performance fuels for enhanced safety and recycling of minor actinides to reduce waste Different fuel Composition (oxide, metal, nitride, carbide, fluoride) Forms (single phase, solution, composite) Packing (pellet, particle, liquid) Images from IAEA

38 38 Advanced and Innovative Technologies Advanced recycling technologies (Partitioning) Aqueous separations Separation of U/Pu and minor actinides, lanthanides and fission products through different cycles Alternative to PUREX: advanced PUREX, TRUEX, DIAMEX, SANEX, TALSPEAK Pyrochemical process ( dry ) Separation of U/Pu from MA and FP from actinides through electrorefining Images from JRC-ITU

39 39 Thorium Fuel Cycle Use Th in fuel (but not fissile) U/Th fuel cycle: 235 U or 233 U used as fissile material; 232 Th used as a fertile material Development of new technologies are needed for: Fuel fabrication Reprocessing and waste management Th fuel cycle under development in India; option kept open and R&D pursued in many other countries

40 40 Summary Nuclear fuel cycle involves different stages and processes: Front-end: Mining, milling, conversion, enrichment and fuel fabrication Power generation Back-end: spent fuel storage, reprocessing, and waste disposal The fuel cycle can be operated as a open, partially closed or closed cycle Today s R&D is dedicated to the development of advanced fuel cycles for the deployment of the next generation of nuclear systems

41 41 References The Nuclear Fuel Cycle: From Ore to Waste, ed. P. Wilson, Oxford University Press

42 Thank you for your attention 42

43 Upcoming NAMP Radiochemistry Webinars Front End: Uranium Mining, Milling, Enrichment and UO2 Production July 24, 2014 Environmental and Human Contamination in the Front End of the Fuel Cycle for Uranium Mining and Milling August 21, 2014 Nuclear Fuel Fabrication September 25, 2014 Visit the NAMP website at