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Nuclear fuels and fuel cycles
Published in Kenneth Jay, Nuclear Power, 2019
Neutron loss per neutron absorbed is made up of four things; first, the essential one neutron to maintain the chain reaction; second, neutrons converting fertile atoms to fresh fissile atoms; third, neutrons absorbed in fuel to form higher, non-fissile, isotopes or in coolant or canning or structural materials; fourth, neutrons leaking out of the system. In a balanced neutron economy (i.e. a steadily-running reactor) production is equal to loss. This may be written as an equation:
Uranium Enrichment, Nuclear Fuels, and Fuel Cycles
Published in Robert E. Masterson, Nuclear Engineering Fundamentals, 2017
A fast breeder reactor is a reactor that uses fast or “high-energy” neutrons to convert Uranium-238 into Plutonium-239. The superior neutron economy of a reactor that uses fast neutrons makes it possible to build a reactor that, after its initial fuel charge of plutonium, requires only natural (or even depleted) uranium to continue making power. It also produces more fissile material than it consumes.
Coolant Materials
Published in C. K. Gupta, Materials in Nuclear Energy Applications, 1989
Besides light water, heavy water is also attractive as a reactor coolant (a coolant-moderator). The only significant difference between light, or ordinary, water and heavy water lies in the appreciably small cross section of the latter for the capture of thermal neutrons. A good moderator, heavy water yields an inherent advantage in neutron economy. The MR is nearly 400 times greater for heavy water than it is for light water (the moderating ratio for heavy water is 21,000, and that for light water is 58). The improvement in neutron economy means that less fissile material is required for making a reactor critical. Use of natural uranium as fuel is entirely feasible. The additional cost of heavy water is not compensated by any gain in coolant properties. The heavy water is therefore, on the first count, normally specified as moderator and may incidently serve as a coolant.
Impact of the Melt-Refining Process on the Performance of Sodium-Cooled Rotational Fuel-Shuffling Breed-and-Burn Reactors
Published in Nuclear Science and Engineering, 2023
Van Khanh Hoang, Odmaa Sambuu, Jun Nishiyama, Toru Obara
Breed-and-burn reactors have been intensively studied as well at the University of California, Berkeley (UCB), in Project No. 09-769 (Ref. 1) and Project No. 12-3486 (Ref. 3); at the Tokyo Institute of Technology with the CANDLE burning fast reactor4; and at TerraPower with the TerraPower Traveling Wave reactor.5 Unlike the cores in other classes of fast reactors, B&B reactors can operate with loading fuel of fertile materials with natural content. Therefore, B&B reactors require high neutron economy to maintain criticality in operation. The feed fuel must be burned to a sufficient level such that the rate of neutron production increases with burnup and overtakes that of neutron absorption in operation. That is, the generated neutrons are equal (or slightly larger) than the total number of neutrons lost, i.e., lost to absorption and also leakage for sustaining the chain reaction that can contribute to the B&B reactor.
Feasibility of Sodium-Cooled Breed-and-Burn Reactor with Rotational Fuel Shuffling
Published in Nuclear Science and Engineering, 2022
Van Khanh Hoang, Odmaa Sambuu, Jun Nishiyama, Toru Obara
In the rotational-fuel-shuffling scheme, the fresh fuel assemblies were loaded at the core periphery and discharged at locations far from the core center. Therefore, the power distributions peaked at the core center and gradually decreased in the radial direction, as presented in Fig. 6. This reduced neutron leakage and improved the reactor’s neutron economy.