How does Reinforced Concrete Protect Nuclear Power Plants against Terrorist Attack?

After twin tower collapsed by terrorist attack, it is seriously studied that how nuclear power plants in United States are safe. In this post I shall discuss how the infrastructure of reactor itself and surrounding structures will response when a terrorist air plane or hijacked plane impacts the nuclear power plants. 

A nuclear power plant's containment structure, which encloses the nuclear reactor, is only a few dozen meters in diameter, very much smaller (and therefore difficult to aim at) than the WTC's towers, which represent a volume larger than a NPP's containment structure by a factor of 100 (at least).

A nuclear power plant's containment structure consists in a more or less 1 meter thick wall of very thick and heavy reinforced concrete : much more resistant than the windows and not-so-thick metallic structures of the WTC.

U S nuclear power plant

If the airplane hits other buildings on the site around it, other than the containment structure, the reactor will automatically stop due to the many independant and automatic security systems (even, in most cases, if the control room was destroyed).

If the airplane hits the side of the circular concrete containement structure (at an angle significantly less than 90°), it will probably just bounce off the side and hardly damage the external structure at all, because the containment structure in most power plants is very heavy, thick and strong and has a more or less circular form (reinforced concrete). 

If the airplane hits the top of the containment structure, it will probably not directly damage the vital structures of the core of the reactor which are, in most installations, located much lower, in the bottom part, or at middle height in the reactor building, and the reactor will stop automatically (the automatic protection against earth-quakes will be activated by the impact). 

If the airplane hits the containment structure in it's middle-height or lower part, which isn't easy because there are many other (non-nuclear) buildings around a nuclear power plant, it will the need to get through not only the very thick external containment, but also several successive reinforced concrete walls (about 20 to 40 centimeters thick each), on most nuclear power plants, before reaching the heart of the reactor itself. The probability that pieces of a large airplane make their way through all these successive walls isn't so certain.

Twin tower collapsed by terrorist attack

- terrorist attacks or plane accidents are in fact taken in consideration when designing nuclear power plants, but only to resist the crash of small airplanes. A large airplane at full speed as in the case of the WTC, may produce some damage to the containment structure and, perhaps, to the reactor itself. 

Thus if these following if’s are happened simultaneously: 

-if the plane doesn't miss the NPP 

-if it hits the concrete containment exactly on the middle, not on the sides 

-if it strikes the containment structure not too high and not too low 

-if it gets through the containment structure 

-if it damages both the (small in volume) core of the reactor or a vital part of the primary circuit), 

-if it also damages several or all the multiple redundant safety systems 

then a bad accident MAY perhaps happen.