NUCLEAR REACTOR FUEL ASSEMBLY Russian patent published in 1997 - IPC

FIELD: nuclear power engineering; nuclear reactors of pressure-tube uranium-graphite type, for example. SUBSTANCE: central rod of fuel assembly has burning-out absorber; specific hydraulic resistivity trough length of internal clearance between rod surface and inner surface of bushing block is lower than that through height of external clearance between external surface of block and channel wall due to at least 1.1 times larger flow section at internal clearance than at external one or due to providing additional labyrinth resistance in external clearance; product of macroscopic absorption section by fissionable material volume referred to sum of products of macroscopic absorption sections and respective volumes of channel, can, insert, coolant, and absorber materials is between 0.3 and 1.1 due to lower macroscopic absorption section of can material than that of coolant or due to change in concentration of burning-out absorber and fissionable material relative to isotope in natural mixture; at faster steaming of coolant in internal clearance than in external one, neutron thermalization region coincides with absorber resonance. Used as burning-out absorber are isotopes of ytterbium, europium, thorium, iridium, rhenium, boron, or their mixture with boron or erbium. EFFECT: improved design. 2 cl, 2 dwg