[en] By means of the inspection vehicle the surfaces at the bottom of a pressure vessel in the dead space between the control rod nozzles is made accessible for the necessary periodical inspections. The vehicle, remote controlled, is moved by its own drive mechanism, transmitting its power by means of rack and pission on a profiled rail. Such a rail is crossing the curved vessel bottom e.g. of a BWR, in an arc-shaped path. It is lying in one of the passages formed by many nozzles. An inspection head, e.g. for ultrasonic or X-ray inspections, carried by the vehicle is put on the free surfaces resp. the webs between the rows of nozzles, through which the vehicle is passing for a number of single measurements by means of an additional drive mechanism. Temperatures of about 300 deg C resp. 50 deg C below the reactor bottom have been accounted for e.g. by means of sping-loaded guide rolls pressed to the rail profile under different angles. (orig./PW)