Also read a few years ago about Scandanavian designs which were essentially in a hole. As long as they were operating the valves which kept water out were closed.

If any critical event occurred, the power to the valves was automatically turned off and the thing flooded.

Sort of like air brakes on a truck. If a line ruptures or one loses pressure for any reason, the brakes come on instantly. The air pressure holds back springs pushing on the brakes.

(Happened to me once driving a mixer with 7 yards of concrete in the back. That mixer went from 25 MPH to 0 in half it's length, threw the motor through the radiator. The broken headlights were under the middle of the truck.

And I thought the world had come to an end. Older truck, the headliner fell down, filled with dust, and the concrete was sloshing back and forth pounding the stanchion which held the barrel and protected me.

The truck did stop though.)

Arf