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Nuclear Fission and Nuclear Energy Production
Published in Robert E. Masterson, Introduction to Nuclear Reactor Physics, 2017
If you think about it, this is true because the sum of the two fragments, plus other particles, and the 2–3 neutrons released per fission (due to the conservation of mass) must always add up to between 236 and 240 AMU. Each fission fragment is produced from the fission of U-233, U-235, or Pu-239 with a predictable probability of occurrence or yield. Each fission reaction produces two fission fragments, and so in 100 nuclear fissions, 200 fission fragments are produced. The fission product yield is usually normalized per fission so that the sum of all the fission products produced equals 100%. The 20 most common fission products produced from the thermal fission of Uranium-235 are shown in Table 7.5. There are about 60 fission products produced in significant quantities in this way. Many of these fission products decay very rapidly and do not exist in the core for a protracted period of time. With the exception of Xenon-135 and Samarium-149, most of them do not have large enough cross sections to impact how a reactor behaves, and so their ability to influence the creation of future neutrons is limited. However, the delayed neutrons that they produce are of great practical importance because these neutrons are what allow a nuclear reactor to be controlled.
Nuclear Fission and Nuclear Chain Reaction
Published in Robert E. Masterson, Nuclear Engineering Fundamentals, 2017
Xenon-135 is important in reactor control theory because it has the highest thermal neutron absorption cross section of any nuclear material known. In other words, it literally soaks up thermal neutrons like a sponge (see Chapter 5). The amount of each fission product produced from the fission of a heavy nucleus is called its yield, and the yield is represented in most nuclear engineering books by the symbol Y. (In other books, the fission product yield is represented by the Greek symbol γ.)
Japanese evaluated nuclear data library version 5: JENDL-5
Published in Journal of Nuclear Science and Technology, 2023
Osamu Iwamoto, Nobuyuki Iwamoto, Satoshi Kunieda, Futoshi Minato, Shinsuke Nakayama, Yutaka Abe, Kohsuke Tsubakihara, Shin Okumura, Chikako Ishizuka, Tadashi Yoshida, Satoshi Chiba, Naohiko Otuka, Jean-Christophe Sublet, Hiroki Iwamoto, Kazuyoshi Yamamoto, Yasunobu Nagaya, Kenichi Tada, Chikara Konno, Norihiro Matsuda, Kenji Yokoyama, Hiroshi Taninaka, Akito Oizumi, Masahiro Fukushima, Shoichiro Okita, Go Chiba, Satoshi Sato, Masayuki Ohta, Saerom Kwon
The JENDL-5 fission product yields are given in the ENDF-6 format (MF8), in which the cumulative yields (MF8 MT459) are calculated to ensure consistency between the independent yield data (MF8 MT454) and the JENDL-5 decay data. In this newly evaluated fission product yield data, the covariance data were also evaluated based on physical constraints, that is (1) conservation of mass number, (2) conservation of charge number, (3) normalization of independent yields, (4) normalization of heavier mass yields, and (5) constraints on England and Rider’s evaluation [292]. Since no description rule of covariance data of fission yields is provided in the ENDF-6 format, we generated the data files in an arbitrary format, which can be found in the JENDL-5 fission product yield sublibrary. It should be noted that the uncertainties given in MF = 8/MT = 454, 459 correspond to the ones derived from the square root of diagonal elements of the covariance data.
235U(n, f) Independent fission product yield and isomeric ratio calculated with the statistical Hauser–Feshbach theory
Published in Journal of Nuclear Science and Technology, 2018
Shin Okumura, Toshihiko Kawano, Patrick Jaffke, Patrick Talou, Satoshi Chiba
Thermal neutron induced fission, such as the U(n,f) or Pu(n,f) reactions, produces roughly 800 primary fission fragments [1] . Since these fission fragments are highly excited, they de-excite by emitting several prompt neutrons and rays to reach their ground or metastable states within a timescale of compound nucleus in the fission process. The independent fission product yield (FPY) , which is a distribution of nuclides after emission of the prompt particles but before beta decay, plays an important role in many applications such as estimation of decay heat [2–4] and delayed neutron emission [5,6] in nuclear reactors, the reactor neutrino study [7], prediction of fission product inventory at each stage of the nuclear fuel cycle, the radioisotope production for medical applications, development of advanced reactor and transmutation systems, fission in the galactic chemical evolution [8], and so on. A demand for high quality data of FPY in such applications is rapidly increasing. New applications may require accurate FPY data at several neutron incident energies, while the current evaluated FPY data files contain only three energy points; the thermal, fast, and 14-MeV incident energies, with an exception of the Pu file in the evaluated nuclear data file, ENDF/B-VII.1 [9], where two energy points (0.5 and 2 MeV) are given in the fast range [10].
Monte Carlo Analysis of Coolant Stream Impurity Gamma Emissions in Gas-Cooled Fast Reactors
Published in Nuclear Technology, 2023
Londrea J. Garrett, Milos Burger, Adam Burak, Xiaodong Sun, Piyush Sabharwall, Igor Jovanovic
To calculate the expected gamma spectra, a series of Monte Carlo simulations was performed using the MCNP6.2 software package23 and the geometries described in Figs. 1 and 2. For these simulations, only the primary radiation interaction is considered as MCNP6.2 does not reliably compute subsequent charge and light transport. For each simulated radionuclide, particles were simulated using the F8 pulse height tally resulting in approximately collisions. The pulse height tally was selected over tallies describing energy deposition as a means of analyzing detector response alone as opposed to material performance. Assuming the use of a commercially available data acquisition unit with a maximum count rate of 0.5 MHz (2-μs dead time),24 the measurement event rate was found to be sufficiently small for pileup effects resulting from the data acquisition system to be considered negligible. To account for pileup from detector properties, the limiting rate was approximated as the inverse of the fluorescence lifetime for scintillator detectors and the inverse of the charge maximum time for semiconductor detectors. Again, pileup could be considered negligible as demonstrated in Table II. To limit the computational cost of the simulations, gamma-ray emissions from radionuclides whose fission product yield is less than , whose gamma-ray decay branching ratio is less than , or whose half-life is greater than years were assumed negligible and not simulated. With the exclusion of the sensing line contents, the elemental compositions and densities of the remaining simulated bodies were modeled based on the data published in Ref. 25.