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

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

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

Conversion Losses 27.10

Global Electricity Consumption China & India

Generating Capacity

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

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

The Front End of the Cycle For Light Water Reactor Fuel

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, U 3 O 8, range from 0.1% to 20% U 3 O 8.

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 in situ leaching (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.

Uranium Mine in Niger (Sahara Desert)

Uranium Metallurgy “Yellowcake”

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 Tailings from Uranium Mining and Milling

Uranium Global Resources

World Uranium Production

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.

or centrifugation

COMURHEX – Malvesi, France U3O8 → UF4

COMURHEX – Pierrelatte, France UF4 → UF6

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 process produces 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'.enrichment process Two enrichment processes exist in large scale commercial use, each uses UF 6 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.

Centrifuge Enrichment Feed Enriched exit Depleted exit U235F 6 is lighter and collects in the center (enriched) U238F 6 is heavier and collects on the outside walls (Depleted/Tails) Feed to Next Stage

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.

Centrifuge Cascade

F6F6 F6F6

Loading uranium hexafluoride containers Gaseous diffusion plant Paducah, Kentucky

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.

UF6 Gas to UO2 Powder to Pellets

Fuel Pellets

Nuclear Fuel Assembly Fuel Pellet

Fuel Assembly for Light Water Reactor

Fuel Assemblies are Inserted in Reactor Vessel

Nuclear Power Reactor

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

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

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

Composition of Spent fuel Rods from a Light Water Reactor MaterialInitial FuelSpent FuelType of Waste Transuranic elements % TRU U % Pu isotopes % TRU Fission products %High Level U %0.08% U %94.3%

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

Fates of Spent Fuel Open Cycle Closed Cycle

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.

Spent Fuel Storage Pools

Dry Cask Storage on Reactor Sites

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

Transport of Spent Fuel

Carlsbad, New Mexico – Waste Isolation Pilot Plant (WIPP) Since 1999 this site stores transuranic waste from clothing, tools, rags, residues, debris, soils, and other items contaminated with radioactive elements mostly plutonium.

Solidifying high-level waste in borosilicate glass for long term storage in a repository

Reprocessing – Closed Fuel Cycle Recovery of uranium and plutonium from spent fuel Reduce volume and radioactivity of waste France, the UK, Japan, and Russia currently reprocess spent fuel

Pu Recovery by Bismuth Phosphate Process Pu is found in low concentrations (<250 ppm) in reactor products. Weapons grade Pu must be chemically pure (< 1 part in 10 7 parts Pu). The Pu recovery for total process was 95% with < 1 part impurity in Pu(s) + X(s) HNO 3 Pu 4+ (aq) + X y+ (aq) H 2 SO 4 Pu 4+ (aq) + X y+ (aq) + Bi 3+ (aq)Pu 3 (PO) 4 (s) +X y+ (aq) + BiPO 4 (s) Pu 3 (PO) 4 (s) +BiPO 4 (s) HNO 3 oxid. agent Pu 6+ (aq) +Bi 3+ (aq) Pu 6+ (aq) +Bi 3+ (aq) H 3 PO 4 Pu 6+ (aq) + BiPO 4 (s) Pu 6+ (aq) H2O2H2O2 PuO 2 2+ (aq)Pu(s) reducing agent X(s) = fission products or uranium; y+ = oxidation state Plutonium was redissolved and further purified using LaF 2 in place of BiPO 4 (s)

Mixed Oxide Fuel (MOX) MOX is produced from the output of reprocessing plants and is a mixture of plutonium and uranium oxides with a composition of 3% to 7% PuO 2 and the rest UO 2. The MOX is then mixed with ordinary LEU uranium-oxide fuel for use in light water reactors. Mixture is 1/3 MOX and 2/3 LEU. By 2001, over 20 power reactors in France were using MOX for one third of their fuel In the US, MOX fuel is being used as a means of disposing of Pu from dismantled nuclear weapons in the US and Russia.

Fuel Reprocessing Plant, Marcoule, France

US Global Nuclear Energy Partnership

Nuclear v. Alternatives ($/MWh) nuclear coal gas wind solar capital O&M fuel total $100/t C new total

Front-end Costs unit costunits/kg$/kg$/MWh Uranium$50/kg10 kg$ Conversion$5/kg10 kg$500.1 Enrichment$100/SWU6 SWU$ Fabrication$250/kg1 kg$ Total$ Assumes fuel with 4.4% U235 and burnup of 50 MW t d/kg, tails assay of 0.3% U235, and efficiency of 33%

Back-end Costs $/kg$/MWh Wet storageincluded in capital, O&M Dry storage$ Geologic disposal$ Total$ Total front + back$

HEU Pu-239

Iranian Nuclear Complex

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

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