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Nuclear Particles, Processes, and Reactions
Published in Robert E. Masterson, Introduction to Nuclear Reactor Physics, 2017
After the fission process is complete, the ejected fission products decay into other fission products, and some of these fission products can absorb almost as many neutrons as the control rods can. Between 50 and 100 different fission products are produced in this process, but only a few of them can affect the way in which a reactor behaves. A fission product that is capable of absorbing large numbers of neutrons is called a neutron poison. By far the most important neutron poison is Xenon-135. It is about 5000 times more likely to absorb a low-energy neutron than a U-235 nucleus is, and because of this, its buildup must be very carefully monitored and controlled over the lifetime of the core.
Fundamental Nuclear Processes: Scattering, Fission, and Absorption
Published in Robert E. Masterson, Nuclear Engineering Fundamentals, 2017
After the fission process is complete, the ejected fission products decay into other fission products, and some of these fission products can absorb almost as many neutrons as the control rods can. Between 50 and 100 different fission products are produced in this process, but only a few of them can affect the way in which a reactor behaves. A fission product that is capable of absorbing large numbers of neutrons is called a neutron poison. By far the most important neutron poison is Xenon-135. It is about 5000 times more likely to absorb a low-energy neutron than a U-235 nucleus is, and because of this, its buildup must be very carefully monitored and controlled over the lifetime of the core.
Nuclear Forensics Methodology for Reactor-Type Attribution of Chemically Separated Plutonium
Published in Nuclear Technology, 2018
Jeremy M. Osborn, Evans D. Kitcher, Jonathan D. Burns, Charles M. Folden, Sunil S. Chirayath
An example of a characteristic ratio useful for determining reactor type is 150Sm/149Sm; the dependency is shown in Fig. 4. 150Sm and 149Sm are stable isotopes and their ratio increases with increasing fuel burnup with a large dependency on the neutron energy spectrum. This behavior is due to the radiative capture cross section of the well-known fission product neutron poison 149Sm, which has a very large reaction cross section for thermal neutron absorption in a reactor. The 150Sm/149Sm ratio value is orders of magnitude larger in the thermal reactors (PHWRs and PWRs) than in the fast reactor (FBR) over the burnup range studied. Other characteristic ratios which will contribute to determination of source reactor type include 135Cs/137Cs, 136Ba/138Ba, 152Sm/149Sm, 240Pu/239Pu, 241Pu/239Pu, and 242Pu/239Pu.