9 uranium mining + is nuclear green Flashcards
beta emitter point source dose rate
800 A mSvh-1 at a distance of 10cm in air
less energetic gamma rays will have
shorter attenuation legths
nuclear is green because
(fossil fuels)
nuclear doesn’t produce same amount of greenhouse gas emissions
nuclear power plants don’t emit air pollutants (so2, VOCs -volatile organic compounds)
reliable stable base energy- compliments variable wind and solar
nuclear is green because
(efficiency)
small amounts of nuclear fuel produces large amuonts of electricity
land efficent
U is more abundant than fossil fuels (have 70yrs of fuel in the mines we currently know about)
nuclear is not green because
(mining)
open pit mining produces lots of spoils/tailings -harmful to enviro (chemicals)
Jet +raise boring- noise and air pollution, disruption to local wildlife, collapse concern, groundwater contamination potential
jet boring
jet blast it out with water, suck it all out
mining (open pit)
need to clear habitats, massive mining sights
scar in landscape
mining (underground types)
cut and fill -back fill everything (labour intensive)
stope and pillar - leave pillars so can’t extract everything
raise boring- drill down corrode it
mining (in-situ leaching)
getting big recently
pump acid into ground, and U leached out into solution
cut out steps- don’t have to crush and preconcentrate
wildlife not as disturbed
U 6
soluble sparkerly
ore milling
turn into yellow cake
vast facilities- huge amount of ENERGY
problem with radioactive dust
grind it
crushing and grinding (1st stage of milling)
uniform size- slowly finer and finer
ENERGY INTENSIVE
VAST mill
powder easier to do chemical process
ENERGY AND WATER WASTAGE
Preconcentraion (2nd milling process)
take out U grains- concentration means more efficient down the line
radiometric sorting, photometric or gravity separation
remove minerals that are likely to hinder Uranium leaching or recovery (increase efficiency)
Provide clean tailings that can be rejected without causing environmental concerns.
radiometric sorting
Efficient, inexpensive process sorting fragments on the basis of radioactivity. Material needs to have:
* Have heterogeneous U concentrations
* Coarse fragmentation (200-250 mm)
* Secular equilibrium between uranium and radium i.e. the isotopic ratio is constant.
gravity seperation -preconcentration
u doesn’t float, quartz floats away
no moving parts so won’t break
sprial- U goes into center as heaviest
leaching (3rd milling process unless in-situ then it’s the 1st)
either acid or alkali leaching is used.
Leaching is performed in stirred tanks, heaps or in-situ.
4 to 6 (U soluble)
Choice of leaching method depends on:
* Ore grade
* Complexity of mineralisation
* Reagent costs
* Time required for solubilisation
* Capital costs
* Operating costs
acid leaching
leaches to heavy metals and contaminants, mobilise metals
would need lots of acid -dangerous
need to cool everything
30% of mills energy consumption
alkaline leaching
less common, less efficient
less enviro implications
less soil acidification & fewer toxins
lower temp and less energy usage
liquid-solid separation (4th milling process)
enhance- ENERGY INTENSE
solution purification (5ht milling process)
ion exchange- more concentrated
uranyl complexes (gets sucked onto) to this resin
product recovery (6th milling process)
dry it into yellow cake
use precipitates to do this
change it back into U4 (immobile)
more energy in drying
yellow cake formular
U3O8
U235 enrichment (centrifuge enrichment)
need to be greater than 3.2% (reactor grade)
normally very small concentration (0.7) so more waste of U238 to enrich the fuel
centrifuge enrichment- mass difference, U238 move to outside via centrifugal forces, have to spin it
many centrifuges, more energy
Purification (final)
before UF4 is formed- yellowcake must be purified
remove- reactor poisons, compounds that form volatile fluorides and impurities
then mix with acid -create UF6
depleted Uranium
waste product of the enrichment process
U238 used as tank armour (dense)
on going problem- hydrogen storage
nuclear isn’t green summary
-mining U process takes a lot of energy
-waste & disposal
-renewable alternatives that don’t require as energy intensive mining and milling nor do they produce the level of waste
-accident risk
-fossil fuel used in fuel transport
accident risk
risk of nuclear accidents
risk to workers at all stages
Cs in soil
remediation efforts disrupt habitats
wildfires can be caused
shooting of livestock and bulldozing
waste disposal
nuclear fuel cycle produces waste at every step
radioactive waste- concern to environment
mill tillings provide contamination hazard
thorium reactors
can use all of Th unlike only 0.7% of uranium
Th is biproduct of rare earths
technology very expensive and only testing rn
gCO2 eq / KWh
coal: 820
nuclear: 12
solar: 41
wind: 11.5
median lifecycle emissions including albedo effect and infrastructure
IPCC report 2014 (Bruckner et. al, 2014)
the question of is an energy source green
has to be compared against other energy sources because no energy source is green
just comparably it is better for the environment that other things
roasting -preconcentraiton
can produce pollutants (SO2) -ACIDIC, METALIC AND TOXIC COMPOUNDS
