Corium (nuclear reactor) from the pre-meltdown reactor or be due to spontaneous fission of reactor-created actinides. In the absence of adequate cooling, the materials inside of the reactor vessel overheat and deform as they undergo thermal expansion, and the reactor structure fails once the temperature reaches the melting point of its structural materials. The corium melt then accumulates at the bottom of the reactor vessel. In the case of adequate cooling of the corium melt, the melt can solidify and the spread of damage is limited to the reactor itself. However, corium may melt through the reactor vessel and flow out or be
Office of Nuclear Reactor Regulation crisis zone in person in order to demonstrate that the dangers were not as high as many believed. These events occurred at approximately the same time as the beginning of the J. Samuel Walker term of service as the official historian of the NRC and are documented by him in "". Office of Nuclear Reactor Regulation The Office of Nuclear Reactor Regulation, usually known by the acronym NRR, is a subordinate part of the United States Nuclear Regulatory Commission. The Office should not be confused with the NRC's Nuclear Regulatory Research. The Office's current Director is William Dean. It has