Neutron absorbers

Purpose: To prevent cloggings of gaps due to falling of neutron absorber fragments thereby preventing the occurrence of local stresses in fuel cans. Constitution: Neutron absorber used for neutron shielding in an LMFBR type reactor comprises a wrapper tube disposed with a handling head at its upper end and an entrance nozzle formed at its lower end and containing neutron absorbers covered with covering material in the wrapper tube. The covering tube for covering the neutron absorbers has a multi-layered tube structure, in which the outer cover tube is made of stainless steels and the inner cover tube is made of a thin plate made of material of lower strength and greater ductility than stainless steels such as pure iron, aluminum or copper, which enables to prevent neutron absorbers from breakage due to thermal expansion and prevent fragments from falling to the outer gaps. In addition, there is no possibility that the outer cover tube and the inner cover tube are brought into contact with each other. (Takahashi, M.)