| 摘要 |
1. Undermoderated nuclear reactor the core of which is immersed in cooling and moderating light water and is constituted of fuel assemblies of prismatic shape arranged side by side and parallel to a same direction, each containing fuel rods (4) having the same diameter and distributed at the nodal points of a regular array, some of the nodal points being devoid of rods, characterized in that it further comprises clusters of elements (8) which contain fertile material, associated with means for moving them between an extracted position out of the core and a position where they are inserted between the rods (4), at nodal points which are devoid of fuel rods, for decreasing the volume of moderator in the core during certain phases at least of reactor operation, and in that the rods have a diameter of about 9.5 mm and a spacing of from 2 to 3 mm whereby the moderation ratio when the fertile material containing elements (8) are extracted is lower than the value corresponding to operation with a thermal neutron spectrum. |
