| abstract |
(57) [Summary] MO based on a novel principle of improving void coefficient A fuel assembly, a fuel rod and a reactor core using X are provided. An upstream blanket (17), an upstream main heat generation area (16), a low concentration area (15), a downstream main heat generation area (13), and a downstream blanket (14) are arranged from upstream to downstream of a fuel assembly (1). It consists of. Low scattering space 6 on downstream blanket 14 And a moderator / coolant space. As the void fraction of the coolant increases, the neutron transfer area (distance) increases, and the dispersed absorber segments can absorb neutrons farther away. On the other hand, since the absorption capacity of the absorber segment is a saturated type, it hardly decreases even when the neutron spectrum is hardened, so that the absorption capacity eventually increases, and the void coefficient can be improved in the negative direction. |