Outline of EU Processing Salvage Operations – Recovering uranium from salvage and by-products Uranium Purification – Separating uranium from impurities.

Outline of EU Processing

• Salvage Operations– Recovering uranium from salvage and by-products

• Uranium Purification– Separating uranium from impurities– Producing pure uranium compounds

• Uranium Metal Production– Converting uranium compounds to pure metal

• Machining

Why Discuss EU Processing?

• Understanding the process is key to performing an adequate NCS analysis!– A lack of understanding might lead to excessive

conservatism - complicated controls– Might lead to a failure to evaluate credible

conditions – incomplete controls

Sources

• Enriched Uranium Processing, Patton, Googin, and Griffith, Pergamon Press Inc. (1963).

• Nuclear Chemical Engineering, Benedict, Pigford, and Levi, McGraw-Hill Inc. (1981)

Salvage Operations - Overview

• Concentration of Combustibles by Ignition– Graphite, absorbent paper, PPE (gloves, booties,

etc), filters, etc.– Muffle furnacing– Destructive distillation

• Leaching– Recovering uranium from ash and other insoluble

materials– Dissolving/acidifying uranium compounds

Salvage Operations - Furnaces

• Muffle Furnace– Single retort (closed vessel with outlet), typically

electric – Combustible batch in a pan– Furnace is supplied air or O2

– Produces a stable uranium-laden ash– Exhaust gas contains entrained uranium and is

filtered

Muffle Furnace

Salvage Operations - Furnaces

• Destructive Distillation– Retort and distillate tank– Combustible batch in a pan– First cycle is distillation– Second cycle is oxidation– Produces a stable uranium laden ash and organic

distillate– Distillate and exhaust gas should not contain much

entrained uranium

Destructive Distillation

Leaching

• Acid washing insoluble materials laden with uranium

• Continuous or batch• Geometry/volume control preferable:– Volume (beakers, flasks, etc.)– Geometry (cylindrical tanks, slab tanks, trays)

• Uranium solution is the product• Leached solids discarded (after confirmation)

Uranium Purification Summary

• Separating uranium from impurities– Solvent extraction– Evaporation

• Production of pure uranium compounds– Molten uranyl nitrate– Denitration– Fluid bed reactors

Solvent Extraction

• Selectively removing uranium from aqueous solution using organic solvents

• Stripping uranium from organic into clean aqueous solutions

• EU recovery may involve two separate solvent extraction processes – primary and secondary

• Utilizes nitric acid chemistry

Salting

• Uranyl nitrate: UO2(NO3)2

• Highly soluble in water• UO2(+2) + 2NO3(-1) ↔ UO2(NO3)2

• Balance between ions and undissociated • Nitrate salts push the equilibrium toward the

undissociated molecule• Undissociated molecule soluble in many

organics solvents (ethers, ketones, and alcohols)– Not paraffins (such as kerosene)

Salting Agents

• Common salting agents include nitric acid and ammonium, sodium, calcium, and aluminum nitrates

• Aqueous feed is loaded with salting agent to favor extraction in organic solvent

Distribution Coefficient• Concentration of component (uranium) in

organic phase to that in aqueous phase

From Benedict, Pigford, and Levi

Organic Solvents

• Dibutyl Carbitol (DBC)– with high nitrate and low acid concentrations, DBC is

efficient in removal of uranium– Product has lower uranium concentration than feed

• Tributyl Phosphate (TBP)– Nitric acid is an efficient salting agent with TBP– High density of TBP requires use of hydrocarbon

diluent– Very little nitric acid extracted– Higher uranium concentrations in aqueous effluent

(raffinate)

Solvent Extraction Flow Sheets

From Benedict, Pigford, and Levi

Solvent Extraction Flow Sheets

From Benedict, Pigford, and Levi

Types of Extraction Equipment

From Benedict, Pigford, and Levi

Primary and Secondary Extraction

• Primary: uses DBC– Advantages: scavenges uranium from feed,

produces low uranium raffinate– Disadvantage: requires substantial salting, product

has low uranium concentration• Secondary: uses TBP diluted in hydrocarbon– Advantages: requires little salting, produces clean

product– Disadvantages: high uranium concentration in

raffinate

Evaporation

ProcessCondensate

SteamCondensate

Evaporation

• Natural circulation• Evaporation rate regulated by steam pressure• Entrained liquid removed (cyclone and

demisters) returned to evaporator• Acid and water vapors condensed• Steam and process condensates discarded• Product withdrawal and feed rate regulated to

maintain target concentration

Production of Pure Uranium Compounds

• Denitration• Precipitation• Reduction

Denitration

• Thermal decomposition of UO2(NO3)2 to UO3

• Evolves water, NOx gasses, and uranium particulate

• Stirring action mills the powder particles• Walls are heated• Product overflows an adjustable dam• Gasses and particulate are treated in a packed

column (dissolver/scrubber)

Stirred-bed Denitrator

From Patton, Googin, and Griffith

Precipitation

• Aqueous (acidic) uranium precipitated by reaction with NH4OH (basic) or H2O2:

• Products are ammonium diuranate (ADU) or uranium peroxide

Precipitation

• pH carefully monitored• Precipitate nonstoichiometric• Consistency of gelatin• Must be dewatered – filtered or centrifuged• Filtrate or centrate discarded; will contain

residual uranium as light, suspended solids• Product collected in container (furnace

crucible or pan)

Supplemental Notes on Uranium Compounds

• Precipitates are converted to dry solids – UO3 – produced at lower temperatures– U3O8 – produced at higher temperatures– UO2 – higher temperatures, requires H and

absence of O2, product unstable in air– UF4 – produced from oxide reaction with HF

• Higher surface area particles are more reactive

• Calciners, furnaces, fluid beds, stirred beds

Uranium Metal Production

• Reduces UF4 to uranium metal by reaction with highly pure magnesium or calcium

• Reactant metal is uniformly mixed with UF4 and charged to the reactor– Typically in a crucible and with a sand liner– Lid secured tightly (energetic reaction)

• High temperature required during and after reaction to promote separation of U from slag

Typical Bomb Reduction Assemblies

From Patton, Googin, and Griffith

Uranium Metal Production

• Contents of the reactor mechanically separated

• Metal regulus is cleaned (pickled)• Slag discarded (could be used as salting agent

for solvent extraction)• Liner fragments discarded• Sand discarded or reused

Machining

• Cutting uranium metal generates heat and requires coolant to prevent fires involving turnings (chips, fines)

• Turnings are valuable and are collected for recovery

• Typically significant amounts are machined to remove surface defects from casting

Machine Lathe

Machining Metal

Machining Metal

Machine Turnings