Nuclear history cycles

A research and development program on the recovery and purification of potentially useful by-product actinides from the nuclear fuel cycle was carried out some years ago in the Federal Republic of Germany as part of the "Actinides Project" (PACT). In the course of this program, procedures for the recovery of neptunium, americium and curium isotopes from power reactor fuels, as well as procedures for the processing of irradiated targets of neptunium and americium to produce heat-source isotopes, have been developed. The history of the PACT Program has been reviewed previously (1). Most of the PACT activities were terminated towards the end of 1973, when it became evident that no major commercial market for the products in question was likely to develop. 

Neutron cycle is die average life history of a neutron m a nuclear reactor. The gain in the number of neutrons in a reactor during any individual neutron cycle ts given by n(k-1). where n is the number of neutrons in the reactor of the beginning of the cycle and k is the multiplication factor. 

Our Galaxy is a collection of gas and stars nearly 13 billion years in age. Throughout its history, gas has condensed into stars. These stars live their lives in stable configurations by burning nuclear fuel which creates new nuclei (7). Once the usable nuclear fuel is exhausted, the star dies and expels its outer layers, thereby enriching the gas between the stars in new isotopes. This gas then can form into new stars, and the cycle repeats. One of the new stars that formed in the Galaxy 4.5 billion years ago is our Sun, and the chemical elements and their isotopes in our Solar System are thus the result of billions of years of Galactic history. 

Geological evidence has indicated that mid- to high-latitude locations in the Northern Hemisphere have experienced glaciation/deglaciation cycles in recent geological history. These cycles are likely to recur in the future within a time frame of several hundred thousand years and have to be considered in performance assessments of deep geological repositories of long lived nuclear wastes. 

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