Solute Travel Times Flashcards
What is one solution of storing nuclear waste as we can’t leave it indefiently in cooling pots
Bury it deep and impermeable so it can’t come back and contaminate is
Why was sellafield chosen
A lot of waste was coming around the country to be processed here anyway and it has deep geology that is the least permeable in the uk anyway
What is at depth beneath sellafield
Borrow dale Volcanic Group TUFF (slowly permeable)
What is the government test for nuclear waste sites
If we put the waste underground and it leaked and comes back to surface within 10,000 years it’s not an acceptable site
What are the chemical issues of burying nuclear waste
Radioactive decay - we should hang on as long as we can bc it gets more stable.
Chemical sorption - ions sorb tO soils qbe rock -> longer travel times do this is good.
What element doesn’t sorb and so there is no retardation and it has fast travel time
Chloride 36
How to work out pore-water velocity
Darcys equation -> average veoclirt over an REV face (area) but actually water is only through part of the face I.e the pores. Must divide Darcys law by porosity
What is the key thing to look at when deciding to put a deposit in
How long Chloride 36 takes to get to the surface
What did the government try to do
Build an underground laboratory but freenpeace saw the rock characterisation facilit would be a huge cavern underground and would be a backdoor to throw nuclear waste in
Example of a borehole in sellafield
Borehole BH9A. Cost 1 million to investigate what was going on
What is the packer test
Borehole year where you drill boreholes and you have inflatable packing units that you pump up to isolate different bits of the aquifer to do your test on
What is the issue under sellafield
Aquifers are used for water supply so don’t want the sandstone and limestone contaminated
In sellafield what would the element have to travel through to get to the surface
400m of TUFF, 300m of St Bees sandstone, 90m it Calder SST and 10m of glacial drift
What is the distance that the elements would be allowed to travel
400m
What was the nirex assessnent
Used medium hydraulic conductivity.
Worked out hydraulic gradient was 0.06 and porosity was 0.41.
To blunt radionuclei to top of tuff it will have decayed away.
400/ 0.00044 = 1,000,000 yrs
What was the green peace assessment
Used highest Ks (precautionary principle)
Found it would only take 100 years before hitting the aquifer.
What is the problem with using the highest Ks value
Assuming the small value you are reflecting on could reflect a whole aquifer is nonsense because if you have a fracture running through the block it has a huge effect on permeability on local scale but not overall. Unrealistic - pessimistic
Problems with using the median Ks
Assumes measurements samples all preferential paths like fractures. If you use the middle value you have to really know the disruption of permeability but only measured a small area.
What does the assessments ignore
Likely Ks patterns - when looking at profile of geology there’s all sort of layers with different permeability which affects how water moves. The contrast of permeability affects how water moves as it would refract and change direction.
What is the most intensive borehole study in the Uk
Sellafield
What does the sellafield study underestimates
The effects of long conductive features like Fleming hall fault which could shoot up thinga to the surface.
Velocity - overestimates travel time.
What does the sellafield assessments need
Model Ks Patterns to dramatically alter the rates of water movement as we know.
Use only large scale Ks values.
