Wednesday, January 23, 2008

Boring story: Rock Mechanics

AECL is humming along nicely, nobody is paying me anything, and my readership numbers are going south. Time for a boring story to put the kiddies asleep!

In university, I went through UofT Engineering Science, and I specialized in Geophysics. It was more of a leftover choice, after I eliminated everything else! About the only thing you could do with this option was go into the oil exploration industry, so for my third year summer, I went to Calgary to work for an oil company.

I hated it! The only good thing was that I went into the mountains every weekend to look at the rocks. I love rocks! After that summer, the oil boom collapsed, and I had to look for another job anyway. I needed a career change, so I did my Masters degree in Rock Mechanics.

The most amazing thing about rocks, is that all rocks have a very similar friction angle. Their 'cohesion', however, varies from ultra-hard granite, to near-sand. Also, rocks are marvelously fractal, meaning that they behave mostly the same, from a very small scale to a very large scale.

My very first work, when I got out of university, was to look at underground structures - tunnels and caverns. It's a bit different to design infrastructure tunnels, than mining. In mining you can take slow, controlled failure, because you can re-excavate access tunnels. In fact, continuous movement is the norm in mines, simply because you are excavating all around and changing the stress fields.

I was looking at the dynamic stability of these tunnels and caverns, particularly for nuclear plants and waste repositories. The waste respository has the difficult problem of excess heat from the fuel bundles, thus it is always heating up, thus the stresses are always changing. On the other hand, a nuclear plant water intake tunnel is quite the simple thing; it should stand up long enough to slap in a thick concrete lining. Nothing much 'dynamic' about these tunnels.

Besides standing up to heat, there is the added problem of low-probability and time-distant events for a nuclear waste repository. Actually anything is better than having the waste hang around in concrete cans, but the 'people' demand 'million year' time frames, simply because someone could dig into an ultra-deep repository and start eating the nuclear fuel.

As you see, there is little rationality in the nuclear waste biz, but it leads to fun things such as determining what happens during the next ice age. (No matter that those cans all get ground up and spat out!). Maybe I will go some more into this the next time.


monado said...

I never thought about heat build-up. Can we use it for steam at a heat exchange?

Harold Asmis said...

You can't do much with low-grade heat, and you want to keep penetrations to a minimum. I did a lot of work with 'hot dry rock' heat extraction, which is a story for another day.

Sahand said...

I am also interesyed in hot dry rock resources and THMC coupled analyses concerned with them.
Nice to visit your page!