Control rods

Purpose: To significantly improve the neutron absorbing performance of control rods for use in a BWR type reactor while avoiding the increase in the weight of the rods. Constitution: Hafnium hydrides are sealed as the hydride of high neutron absorbers into poison tubes contained in each blade of a control rod. With such a structure, thermal neutrons released from fuel rods and entered into the control rod are absorbed in the high neutron absorbing substance Hf of the hydride of the high neutron absorbers situated to the outer and the inner circumferences thereof. While on the other hand, fast neutrons collide against hydrogen atoms H of the hydride in the high neutron absorbers situated at the outer and the inner circumferences and converted into thermal neutron. The thermal neutrons are instantly absorbed into the surrounding high neutron absorbing substance Hf. The hydride usable herein may also include each of hydrides of Eu, Dy, Gd, Sm, In, B and Cd. (Seki, T.)