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The radiation background
Published in R.J. Pentreath, Nuclear Power, Man and the Environment, 2019
The two stable nuclides formed, 95Mo and 139La, have collectively 135 neutrons, 7 neutrons having been lost via beta decay (see chapter 1) leaving a deficit of 2 neutrons. A more detailed budget analysis reveals that, in fact, some mass has been converted into energy; mass equivalent to ~0.2 atomic mass units. One atomic mass unit (mu) is 1.6605 × 10 -27 kg, and is approximately the mass of one neutron or proton. The energy equivalent to 0.2 mu is ~200 MeV. This energy – part of the binding energy of the large uranium nucleus – is converted principally into kinetic energy of the fission fragments. Some of it is also converted into the energy of the fission neutrons – some of which will cause the fission of other uranium nuclei – and the energy of beta particles, gamma rays and neutrinos. Occasionally – in about 0.25% of thermal-neutron fissions – three nuclei are formed, a process termed ternary fission. The third nucleus is usually an alpha particle but in a few cases it is tritium, 3H. Even rarer, in about 0.001% of 235U fissions, three of four nuclei of approximately similar mass are formed.
Cooling and Disposing of the Waste
Published in Geoffrey F. Hewitt, John G. Collier, Introduction to Nuclear Power, 2018
Geoffrey F. Hewitt, John G. Collier
A material of great interest in radiological protection is plutonium-239, which also has a long biological half-life (200 years in the bone structure and 500 days in the lung). Since the radioactive half-life of plutonium is about 25,000 years, the effective half-life in the body is dominated by the biological half-life. Another important radioisotope, tritium, is emitted in small quantities from water reactors and reprocessing plants. It is formed by the process of ternary fission, in which three, rather than the usual two, fission products are formed. The third fission product is often tritium, and since its molecular size is very small, it can diffuse through the canning material into the coolant circuit. It emits beta radiation and has a radioactive half-life of 12.6 years. Its biological half-life is around 12 days.
New Energy Sources
Published in Fang Lin Luo, Hong Ye, Renewable Energy Systems, 2013
Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts (lighter nuclei) It often produces free neutrons and photons (in the form of gamma rays) and releases a tremendous amount of energy The two nuclei produced are most often of comparable size, typically with a mass ratio around 3:2 for common fissile isotopes [1]. Most fissions are binary fissions, but occasion-ally (2–4 times per 1000 events) there can be three positively charged fragments produced in a ternary fission.
Modeling Tritium Retention in Graphite for Fluoride-Salt-Cooled High-Temperature Reactors
Published in Nuclear Technology, 2021
Kieran Dolan, Steven Huang, Micah Hackett, Lin-Wen Hu
Tritium production in TRIDENT is calculated from the reactions in Eqs. (1) and (2) only, since these reactions will typically account for over 98% of tritium generation in a Flibe-cooled fission reactor.30 Other sources of tritium will also exist besides neutron reactions with Flibe. For example, ternary fission was evaluated to produce 1.3% of the tritium generation compared to the sum of 6Li and 7Li reactions in a 1-GW(electric) commercial-scale MSR (Ref. 10). Ternary fission is currently neglected for FHRs in TRIDENT because of the small contribution to total generation as well as the decreased mobility of tritium generated in the fuel compared to tritium produced in the salt coolant. For the modeled Flibe reactions, all isotopic concentrations are assumed to be steady with time except for 6Li, which has a significant relative change because of its low isotopic concentration in the 7Li enriched salt. To simplify the baseline model, an equilibrium tritium generation rate is used based on the generation calculations for the Mk-1 FHR (Ref. 13).
Evaluation of fission product yields and associated covariance matrices
Published in Journal of Nuclear Science and Technology, 2021
Kohsuke Tsubakihara, Shin Okumura, Chikako Ishizuka, Tadashi Yoshida, Futoshi Minato, Satoshi Chiba
The number of nucleons in a fissioning system should be conserved as , where , and are the proton and the nucleon numbers of the -th fission product and the latter of the compound nucleus. is the average mass number of light-charged particles from ternary fission such as proton, triton, and particles, respectively. Here stands for the prompt neutron multiplicity. The and data were primarily taken from the compilation of England and Rider [3]. See Table 1 for more details.
Evaluation of tritium release into primary coolant for research and testing reactors
Published in Journal of Nuclear Science and Technology, 2021
Inesh Kenzhina, Etsuo Ishitsuka, Keisuke Okumura, Hai Quan Ho, Noriyuki Takemoto, Yevgeni Chikhray
The sources and mechanism for the tritium release into the primary coolant in the JMTR and the JRR-3M were evaluated, and the following results are obtained. – The calculation method for the recoil release rate by PHITS was studied, and the proportional constants of the recoil release rate for the 6Li(nt,α)3H reaction and ternary fission were shown for the neutron reflector materials,– Tritium release by the chain reaction for 9Be is at least two orders larger than that of other reactions, and the chain reaction of 9Be only is sufficient for the evaluation of actual tritium release into the primary coolant,– Calculations of tritium recoil release from beryllium reflectors by simple equation are carried out, and the calculated results agree well with the trend of measured data,– Average neutron flux and spectrum for beryllium reflectors could be used to evaluate with sufficient accuracy.