Nuclear reactor accidents in the United States the Joint Committee on Atomic Energy that: "the cumulative effect of all design defects and deficiencies in the design, construction and operations of nuclear power plants makes a nuclear power plant accident, in our opinion, a certain event. The only question is when, and where. On March 28, 1979, equipment failures and operator error contributed to loss of coolant and a partial core meltdown of Unit 2's pressurized water reactor at the Three Mile Island Nuclear Power Plant in Pennsylvania. The scope and complexity of this reactor accident became clear over the course of five days, as a number of
Nuclear reactor safety system must be developed such that it absorbs as little radiation as possible. For this reason, materials such as magnesium and zirconium are used for their low neutron capture cross sections. The reactor vessel is the first layer of shielding around the nuclear fuel and usually is designed to trap most of the radiation released during a nuclear reaction. The reactor vessel is also designed to withstand high pressures. The primary containment system usually consists of a large metal and concrete structure (often cylindrical or bulb shaped) that contains the reactor vessel. In most reactors it also contains the radioactively contaminated