The unusual nature of the September 11, 2001, terrorist attacks on America (no one had ever intentionally flown commercial airplanes into buildings before) jarred the nation’s security experts from complacency. In a matter of hours, their notions about what constituted the most serious threats to the nation’s security were shattered. Realizing that old thinking about conventional threats would no longer suffice, they quickly began to predict new threats. One threat immediately came to the fore: Terrorists could intentionally crash a commercial airliner into one of America’s 103 operating nuclear power plants.

Intense debate has exploded over whether or not a commercial airliner could seriously damage the containment shell of a nuclear reactor. Reactors were designed to withstand attacks by small planes and vehicles filled with explosives, but no one had envisioned terrorists crashing an airliner...