CBFalconer <cb********@yah oo.com> wrote in message news:<40******* *******@yahoo.c om>...
"Robert W. McAdams" wrote:
... snip ...
Technologies already exist for isolating nuclear wastes from the
biosphere for that period of time. (In fact, the best of these
technologies utilizes a layered approach, in which a number of
isolation techniques are used together, each of which, by itself,
is capable of isolating the waste from the biosphere for
substantially more than 10,000 years.)
All of which is experimentally verified, of course. I am
gratified to know that my public spirited ancestors of 8000 BC
prepared those test beds for you. </sarcasm>
Well, they had find something to do after spending 710,000,000 years
verifying that the halflife of Uranium 235 is 710,000,000 years!
Of course, I'm joking. It doesn't take 710,000,000 years to verify
that the halflife of Uranium 235 is 710,000,000 years any more than it
takes 10,000 years to verify the technology needed to isolate
radioactive waste for 10,000 years.
Let's look at the technology in more detail:
The first part of the plan is to store the waste in salt deposits
(e.g., in New Mexico) that are deep underground, and therefore
isolated from the biosphere. Geologists tell us that these deposits
have been stable for a long, long time, and will remain stable for a
long, long time.
But let's imagine that the geologists are wrong, and that groundwater
begins to seep in and erode the salt before the 10,000 years are up.
How long will it take for the water to get to the waste? The answer
is: approximately 1,000,000 years. How do we know that? Because we
know how thick the salt is, we know how much groundwater there is, and
we can measure how long it takes for a given amount of water to
dissolve a given amount of salt.
But let's imagine that that's somehow wrong, and that groundwater
reaches the area where the waste is stored. Well, then it encounters
a clay backfill that surrounds each container of waste. The clay
swells up when wet to form a tight seal keeping the water away from
the containers of waste.
But let's imagine that the water somehow breaks through the seal
created by the clay. Well, next it encounters the metal casing, which
is designed to be very resistant to corrosion. One of the favorite
materials for the casing is a titanium alloy. Tests conducted in a
abnormally corrosive solution kept at 450 degrees F indicate that it
would survive under those conditions for a thousand years, but in
normal groundwater at the expected repository temperature of 250
degrees F, the casings would retain their integrity for hundreds of
thousands of years.
But what if somehow the groundwater got past all these barriers and
actually reached the waste? That's bring us to the final barrier,
which is that the waste has been reprocessed into a glass which is not
readily dissolved. A Canadian experiment performed with waste glass
in the 1970s indicated that it dissolves in groundwater at a rate of
1/100,000,000 per year, meaning that it would take 100,000,000 years
to completely dissolve.
Bob
