Abstract: An instrumented capsule for nuclear fuel irradiation tests in research reactors includes an outer shell; a rod tip assembly assembled to a lower end plate of the shell, thus absorbing impact; fuel rod assemblies supported in the shell by means of support tubes and housing therein, sintered fuel bodies and in-capsule instruments, such as thermocouples and self-powered neutron detectors (SPND); a protective tube connected to the upper end plate and protecting instrument control cables; and a guide pipe connected to the inclined extension part of a junction tree and guiding the instrument control cables to a control unit provided outside the reactor.