The U.S. Nuclear Regulatory Commission requires all nuclear plants to be able to withstand the most severe natural phenomena historically reported in a 200-mile area around each plant.
Constellation’s nuclear plants are designed to withstand extreme environmental hazards like floods and earthquakes. Watertight doors, elevation of equipment above potential flood levels, and engineered flood barriers protect emergency systems. Plant foundations, structures, and equipment are designed to withstand severe ground motion and flooding.
Defense-in-depth design ensures redundant, diverse, and reliable safety systems to supply water to the reactor core. Every safety system has at least one independent back-up system, and many have more than one.
Plant safety systems are also run by multiple, redundant power sources. Certain equipment is designed to automatically shut down the plant if the need arises due to a condition outside of normal operations.
Multiple physical barriers further serve to strengthen nuclear structures for safety. The first barrier is the fuel itself: the solid, ceramic uranium pellets. Pellets are sealed in metal fuel rods. The fuel rods are made of the metal alloy zirconium, which resists heat, radiation, and corrosion. The rods are bundled together into fuel assemblies.
Fuel assemblies make up the nuclear reactor core. The reactor core is inside the reactor vessel, which has steel walls that are about six inches thick. The reactor vessel sits inside a containment structure made of steel-reinforced concrete and is about five feet thick.
All of these layers are inside the reactor building, which is made of steel-reinforced concrete that is about four feet thick.
After the earthquake-related accident at Japan’s Fukushima Daiichi facility in 2011, the U.S. nuclear industry created the FLEX plan, a major step in addressing the critical problems encountered in the incident: loss of power and reactor cooling capability.
In the FLEX plan, vital back-up emergency equipment—generators, battery packs, pumps, air compressors, and battery chargers—is stored on site at each nuclear facility and also at two regional secure, offsite locations across the country. In a system with layers of built-in redundancy, FLEX provides yet another layer of backup power after a catastrophic event.