Physical particularities of nuclear reactors using heavy moderators of neutrons
- National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) (Russian Federation)
In nuclear reactors, thermal neutron spectra are formed using moderators with small atomic weights. For fast reactors, inserting such moderators in the core may create problems since they efficiently decelerate the neutrons. In order to form an intermediate neutron spectrum, it is preferable to employ neutron moderators with sufficiently large atomic weights, using {sup 233}U as a fissile nuclide and {sup 232}Th and {sup 231}Pa as fertile ones. The aim of the work is to investigate the properties of heavy neutron moderators and to assess their advantages. The analysis employs the JENDL-4.0 nuclear data library and the SCALE program package for simulating the variation of fuel composition caused by irradiation in the reactor. The following main results are obtained. By using heavy moderators with small neutron moderation steps, one is able to (1) increase the rate of resonance capture, so that the amount of fertile material in the fuel may be reduced while maintaining the breeding factor of the core; (2) use the vacant space for improving the fuel-element properties by adding inert, strong, and thermally conductive materials and by implementing dispersive fuel elements in which the fissile material is self-replenished and neutron multiplication remains stable during the process of fuel burnup; and (3) employ mixtures of different fertile materials with resonance capture cross sections in order to increase the resonance-lattice density and the probability of resonance neutron capture leading to formation of fissile material. The general conclusion is that, by forming an intermediate neutron spectrum with heavy neutron moderators, one can use the fuel more efficiently and improve nuclear safety.
- OSTI ID:
- 22614024
- Journal Information:
- Physics of Atomic Nuclei, Vol. 79, Issue 9-10; Other Information: Copyright (c) 2016 Pleiades Publishing, Ltd.; Country of input: International Atomic Energy Agency (IAEA); ISSN 1063-7788
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
22 GENERAL STUDIES OF NUCLEAR REACTORS
BREEDING
BURNUP
CROSS SECTIONS
FAST REACTORS
FERTILE MATERIALS
FISSILE MATERIALS
INTERMEDIATE NEUTRONS
MASS NUMBER
MODERATORS
NEUTRON REACTIONS
NEUTRON SPECTRA
NUCLEAR DATA COLLECTIONS
PROTACTINIUM 231
RESONANCE NEUTRONS
THERMAL NEUTRONS
THORIUM 232
URANIUM 233