The Nuclear Fuel Cycle

Presentation

Components of the Fuel Cycle

Front End

Service Period (conversion of fuel to energy in a reactor)

Back end

Storage (open cycle)

Reprocessing (closed cycle)

Alternatives and Economics

Proliferation Concerns

The Front End of the CycleFor 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, U3O8, range from 0.1% to 20% U3O8.

Uranium Mining Open pit mining is used where deposits are close to the surface

Underground mining is used for deep deposits, typically greater than 120m deep.

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 governedby the nature of the ore body, safety and economic considerations.

In the case of underground uranium mines, special precautions, consisting primarilyof increased ventilation, are required to protect against airborne radiation exposure.

Uranium Mine in Niger (Sahara Desert)

Uranium Metallurgy

Yellowcake

More than 200 pounds of byproduct material, tailings, are typically produced for each pound of uranium.

After extraction of uranium from the ore, the tailings contain much of their original radioactivity.

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

Enriching Uranium for Reactor Fuel Increase the concentration of fissionable U-235 isotope

Enrichment requires a physical process since U-235 and U-238 have the same chemical properties

Physical processes require gases for separation

Uranium and its oxides are solids

Must convert uranium to UF6

Enriched UF6 must be converted back to solid uranium or uranium oxide

or centrifugation

COMURHEX Pierrelatte, FranceUF4 UF6

EnrichmentThe two method of uranium enrichment are:

Gaseous diffusion (older)

Centrifugation (newer)

Both use small differences in the masses (< 1%) of the U-235F6 and U-238F6 molecules to increase the concentration of U-235.

F6F6

Loading uranium hexafluoride containersGaseous diffusion plantPaducah, Kentucky

Centrifuge EnrichmentFeedEnriched exitDepleted exitU235F6is lighter and collects in the center(enriched)U238F6 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 usedin 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.

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 1400C).

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.

UF6 Gas to UO2 Powder to Pellets

Fuel Pellets

Nuclear Fuel AssemblyFuel Pellet

Basic Pressurized Water Reactor (PWR)FuelRods

Fuel Assemblies are Inserted in Reactor Vessel

U-235Pu-239Pu-240AmountTime in reactorRemoval of fuel elementsfor making weaponsProduction of plutonium in a nuclear reactor92U238 + 0n1 => 94Pu239 + 2(-10)In addition to the fission of U-235 atoms, some U-238 atom absorb neutrons and emit beta particles to become plutoniumFission of Pu produces about 1/3 energy from the reactor

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

Composition of Spent fuel Rods from a Light Water ReactorMaterialInitial FuelSpent FuelType of WasteTransuranic elements0.0000.065% TRUU-2360.0000.46%Pu isotopes0.0000.89% TRUFission products0.0000.35%High LevelU-235 3.3%0.08%U-238 96.7%94.3%TUR = transuranic

The actinides are the fifteen elements with atomic numbers 89 to 103. Fission products have shorter half-lives and higher activities.

Actinides have longerhalf-lives and loweractivities

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

Transport of Spent Fuel

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

Reprocessing Closed Fuel CycleRecovers of uranium and plutonium from spent fuel

Reduces volume and radioactivity of waste

France, the UK, Japan, and Russia currently reprocess spent fuel

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% PuO2 and the rest UO2. The MOX is then mixed with ordinary LEU uranium-oxide fuel for use in lightwater 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 fromdismantled nuclear weapons in the US and Russia.

Fuel Reprocessing Plant, Marcoule, France

Relative Costs

Process$/kg fuelUranium$500Conversion$50Enrichment$600Fabrication$250Wet storageIncluded in capital & O%MDry cast storage$200Geological storage$400Total Cost$2000

Proliferationof Nuclear Materials and Weapons

HEUPu-239

Iranian Nuclear Complex

Yongbyon Site

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

Three Useful Educational Resources

The Alsos Digital Library for Nuclear Issues

Nuclear Chemistry in the Community

Concept Map for Nuclear Power

Concept Map for Civilian and Military Uses of Nuclear Energyhttp://www.chemcases.com/nuclear/index2.html#concept

http://alsos.wlu.edu/

http://alsosconceptmap.wlu.edu/nuclearpower/main/index.html

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