"60 Minutes" broadcast the footage from that test a couple weeks ago. In 1979, the US government mounted a 40,000 pound F-4 Phantom II figher on a test track. They used rocket engines to accelerate the plane to 400 MPH. The plane then hit a 6 foot thick piece of concrete built to the same specifications as a nuclear containment building. The plane didn't penetrate more than an inch.

The containment building on a US nuclear powerplant is typically a domed structure made of reinforced concrete several feet thick. For example, here's some info on the Wolf Creek Nuclear Powerplant in Kansas. The walls are 3-4 feet thick. A small plane wouldn't do anything to a containment building.