19 - Reactor Safety

Abstract

Thus chapter describes the dependence of numbers of neutrons and reactor power on the multiplication factor, which is, in turn, affected by temperature and control rod absorbers. The multiplication of neutrons is a reactor can be described by the effective multiplication factor k. The inherent nuclear control provided by delayed neutrons is aided by proper design of the reactor to favor certain feedback effects. These are reductions in the neutron multiplication factor resulting from increases in reactor power. With additional heat input, the temperature increases and the negative reactivity tends to shut the reactor down. Design choices include the size and spacing of fuel rods and the soluble boron content of the cooling water. One of the temperature effects is simple thermal expansion. The moderator heats up and expands, the number density of atoms is reduced, and neutron mean free paths and leakage increase, while thermal absorption goes down. Prevention of release of radioactive fission products and fuel isotopes is the ultimate purpose of safety features. Inherent reactor safety is provided by delayed neutrons and temperature effects. Control rods permit rapid shutdown, and reactor components are designed and constructed to minimize the chance of failure. Equipment is installed to reduce the hazard in the event of an accident. Licensing is administered by a federal agency.