At the time most nuclear power plants now operating were conceived and constructed, part of the over all fuel cycle scheme was that the spent nuclear fuel from these plants would be shipped to a fuel reprocessor where the plutonium and other fissionable material would be separated from the radioactive residue. Consequently, a typical nuclear power station is designed to have within its' site boundaries, facilities for storing only enough spent nuclear fuel to allow the short lived radioactivity to decay for a period of approximately one year before this fuel would be shipped off-site. For various reasons, it may be necessary at some time during the operation of the reactor, to unload the entire core from a typical nuclear power plant. Consequently, the spent fuel storage pools were designed to hold the amount of fuel discharged in one year (or approximately one/third of a reactor core) plus the entire contents of the reactor core. Recent government decisions, however, have stopped the reprocessing of spent nuclear fuels, and until new government policies are developed regarding long-term storage of the fuel, it has become necessary for the typical utility to store nuclear fuel on-site for much longer than one year. Clearly this situation has required extensive modification and expansion of the on-site fuel storage pools, including the installation in many cases of high density fuel storage racks containing nuclear poisons to prevent accidental criticality(1).
