The human element - By Hugh Gusterson

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5. Inherently Safe Reactors

One approach to safety that side-steps the problem of human error is to have reactors that are inherently safe. That is they rely on the laws of physics for their safety and don't let the human make an error.

This type of design is not unique to reactors; it is found in many fields, like airplanes. The Ruttan-designed Vari-EZ airplane is one type of inherently safe design when it comes to preventing wing stall. In a stall, the wing loses lift because the angle of attack is too great. The proper recovery is for the pilot to lower the nose and decrease the angle of attack. However, there is a natural tendency of a pilot to "pull up" when encountering a stall and that is precisely the WRONG thing to do.

Ruttan designed the Vari-EZ with the wing located to the rear of the center. In front, there is a smaller wing called a "canard" that is designed to stall before the main wing. The carnard also keeps the nose up since the main wing is located so far aft. Before the main wing stalls, the canard wing stalls. When the canard stops providing lift to hold up the nose, the nose is lowered, which is precisely what needs to be done. It doesn't matter if the pilot is trying to pull the nose up; that canard is going to stall and pitch the plane down regardless of what the pilot does.

One can design nuclear reactors with the same type of response where the laws of Physics ( which always work ) can do the right thing, even if the operator makes an error. The Argonne Integral Fast Reactor (IFR) was once such reactor, which also addressed the nuclear waste problem:

http://www.pbs.org/wgbh/pages/frontline/shows/reaction/interviews/till.html

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