Tuesday, May 19, 2009

Seismic Capacity and the Chalk River Glass Jaw

Such a delicate flower! ..... Actually, I just took this picture on my fox walk, and wanted to show it off.

But I digress.... Seismic capacity is defined as the amount of 'hit' that a structure can take. We use it all the time in seismic margin assessments. I prefer to define it in terms of Peak Ground Velocity (PGV), which has a very strong world-wide correlation with damage.

A 'Glass Jaw' is what we call a boxer who can't take a hit.

When we had two earthquakes near Pickering, I discovered that people were quite sensitive to PGV on rock of 1 mm/sec. Actually, nobody on rock felt them, it was only people in rickety buildings on swamp. Using a conservative value for amplification of a factor of 10, that gives us about 1 cm/s to scare the bejeebies out of people.

Now, from Taiwan experience, it takes about 50 cm/s to structurally damage housing in Taiwan, which I take to be about the lowest level for structures. This is also the level where you find it difficult to stand up. An enterprising student could take an accelerometer on to the subway! From local experience with the Cleveland earthquake, I estimate 10-20 cm/s to tear the shit out of shopping malls, crack all your drywall, and knock things off shelves.

Japanese reactors get damaged at the very high level of 200 cm/s (2 m/s).

Where does the disintegrating Chalk River fit into this? If any structure is in a state of decay, these seismic capacities zoom down to the floor, sort of like stock values. Housing that has settlement distress is very low, as well as sunken transformers at Pickering! You can tell the degree of decay by looking at the response to very low disturbances.

Now the NRU was exposed to a trifling power disturbance. Nevertheless, this must put in a good shudder at about 1 cm/s as the pumps seize up. The emergency cooling, scramming, etc, must put in an equivalent of 10 cm/s. Did the reactor just shrug this hit off like Tyson? Noooo! It was damaged. Thus, I put the seismic capacity at a ridiculously low value of 10-20 cm/s.

That pretty well means an M5 in the area will create Hell on Earth. And these are a dime a dozen for that zone. Anything bigger will split the tub and expose all the hot fuel bundles. Although this has very low fuel inventory, nothing like Chernobyl, I am sure things will get contaminated a few km, and the river will give free dental x-rays.


Silver Fox said...

Nice flower picture - forget me nots?

Harold Asmis said...

I don't have a clue!