Uranium to Electricity: The Chemistry of the Nuclear Fuel Cycle Dr. Frank A. Settle

1. Uranium to Electricity: The Chemistry of the Nuclear Fuel Cycle Dr. Frank A. Settle Visiting Professor of Chemistry Washington and Lee University Lexington, VA 24450

2. Presentation • Background • Components of the Fuel Cycle • Front End • Service Period (conversion of fuel to energy) • Back end • Storage • Reprocessing • Alternatives and Economics • Proliferation Concerns

3. How is the 2007 Israeli air strike on a Syrian reactor connected to the nuclear fuel cycle?

6. Conversion Losses 27.10

8. Global Electricity Consumption China & India

9. Generating Capacity

10. The 15 Wedge Approach to Energy Demands (Scientific American, 9/06) Double Nuclear Capacity

12. The Nuclear Fuel Cycle (Low enriched uranium LEU 3-5% U-235) (natural uranium)

13. The Front End of the Cycle For Light Water Reactor Fuel

14. Uranium • URANIUM is a slightly radioactive metal that occurs throughout the earth's crust. • It is about 500 times more abundant than gold and about as common as tin. • It is present in most rocks and soils as well as in many rivers and in sea water. • Most of the radioactivity associated with uranium in nature is due to other materials derived from it by radioactive decay processes, and which are left behind in mining and milling. • Economically feasible deposits of the ore, pitchblende, U3O8, range from 0.1% to 20% U3O8.

15. Uranium Mining Both excavation and in situ techniques are used to recover uranium ore. • Open pit mining is used where deposits are close to the surface and underground mining is used for deep deposits, typically greater than 120m deep. • An increasing proportion of the world's uranium now comes from insituleaching (ISL), where oxygenated groundwater is circulated through a very porous ore body to dissolve the uranium and bring it to the surface. ISL may use slightly acidic or alkaline solutions to keep the uranium in solution. The uranium is then recovered from the solution. • The decision as to which mining method to use for a particular deposit is governed by the nature of the ore body, safety and economic considerations. • In the case of underground uranium mines, special precautions, consisting primarily of increased ventilation, are required to protect against airborne radiation exposure.

16. Uranium Mine in Niger (Sahara Desert)

17. Uranium Metallurgy “Yellowcake”

18. “Yellowcake”

19. Tailings from Uranium Mining and Milling DOE classifies the tailings or waste produced by the extraction or concentration of uranium or thorium from their ores as 11e(2) byproduct material. More than 200 pounds of byproduct material are typically produced for each pound of uranium. After extraction of uranium from the ore, the tailings contain much of their original radioactivity in the form of alpha-emitting uranium, thorium230, radium226, and daughter products such as radon222 gas. The total radioactivity present in mill tailings can exceed 1,000 picocurie per gram. Toxic heavy metals, including chromium, lead, molybdenum, and vanadium, are also present in this byproduct material in low, but significant, concentrations

20. Uranium Global Resources

21. World Uranium Production

22. Conversion • The product of a uranium mill is not directly usable as a fuel for light water nuclear reactors. Additional processing, generally referred to as enrichment, is required for these reactors. This process requires the conversion of uranium to gaseous uranium hexafluoride. • At a conversion facility, uranium is first refined to uranium dioxide, which can be used as the fuel for heavy water reactors that do not require enriched uranium. Most is converted into uranium hexafluoride for enrichment. It is shipped to the enrichment facility in strong metal containers. The main hazard of this stage of the fuel cycle is the use of hydrogen fluoride.

23. or centrifugation

24. COMURHEX – Malvesi, France U3O8 → UF4

25. COMURHEX – Pierrelatte, FranceUF4 → UF6

26. Enrichment • Natural uranium consists, primarily, of a mixture of two isotopes (atomic forms) of uranium. Only 0.7% of natural uranium is "fissile", or capable of undergoing fission, the process by which energy is produced in a nuclear reactor. The fissile isotope of uranium is uranium 235 (U-235). The remainder is uranium 238 (U-238). • In the most common types of nuclear reactors, a higher than natural concentration of U-235 is required. The enrichment processproduces this higher concentration, typically between 3.5% and 5% U-235. This is done by separating gaseous uranium hexafluoride into two streams, one being enriched to the required level and known as low-enriched uranium. The other stream is progressively depleted in U-235 and is called 'tails'. • Two enrichment processes exist in large scale commercial use, each uses UF6 as feed: gaseous diffusion and gas centrifuge. They both use the physical properties of molecules, specifically the 1% mass difference, to separate the isotopes. The product of this stage of the nuclear fuel cycle is enriched uranium hexafluoride, which is reconverted to produce enriched uranium oxide.

27. Centrifuge Enrichment Feed Feed to Next Stage Depleted exit Enriched exit U238F6 is heavier and collects on the outside walls (Depleted/Tails) U235F6is lighter and collects in the center (enriched)

28. The gas centrifuge process has three characteristics that make it economically attractive for uranium enrichment: Proven technology: Centrifuge is a proven enrichment process, currently used in several countries. Low operating costs: Its energy requirements are less than 5% of the requirements of a comparably sized gaseous diffusion plant. Modular architecture: The modularity of the centrifuge technology allows for flexible deployment, enabling capacity to be added in increments as demand increases.

29. Centrifuge Cascade

30. F6 F6

31. Gaseous diffusion plant Paducah, Kentucky Loading uranium hexafluoride containers

32. Fuel Fabrication • Reactor fuel is generally in the form of ceramic pellets. These are formed from pressed uranium oxide which is sintered (baked) at a high temperature (over 1400°C). The pellets are then encased in metal tubes to form fuel rods, which are arranged into a fuel assembly ready for introduction into a reactor. The dimensions of the fuel pellets and other components of the fuel assembly are precisely controlled to ensure consistency in the characteristics of fuel bundles. • In a fuel fabrication plant great care is taken with the size and shape of processing vessels to avoid criticality (a limited chain reaction releasing radiation). With low-enriched fuel criticality is most unlikely, but in plants handling special fuels for research reactors this is a vital consideration.

33. UF6 Gas to UO2 Powder to Pellets

34. Fuel Pellets

35. Nuclear Fuel Assembly Fuel Pellet

36. Fuel Assembly for Light Water Reactor

37. Fuel Assemblies are Inserted in Reactor Vessel

38. Nuclear Power Reactor

39. PWR Reactor Vessel • 41 feet tall • 14 feet ID • 8.5 inch thick walls • 665 tons

40. Production of plutonium in a nuclear reactor U-235 Pu-239 Pu-240 Amount Removal of fuel elements for reprocessing Time in reactor

41. Back End of the Fuel Cycle (Open vs. Closed Cycles)

42. Composition of Spent fuel Rods from a Light Water Reactor Material Initial Fuel Spent Fuel Type of Waste Transuranic elements 0.000 0.065% TRU U-236 0.000 0.46% Pu isotopes 0.000 0.89% TRU Fission products 0.000 0.35% High Level U-235 3.3% 0.08% U-238 96.7% 94.3%

43. The actinides are the fifteen elements with atomic numbers 89 to 103.

45. Fates of Spent Fuel Closed Cycle Open Cycle

46. The spent fuel removed from the reactors continues to release heat and is still radioactive. It is, for those reasons, that the fuel is initially stored under water in the spent fuel storage pools.

47. Spent Fuel Storage Pools

48. Dry Cask Storage on Reactor Sites

49. Open Cycle Storage – Current Status in US for Typical Power Reactors

50. Transport of Spent Fuel