A grid strap includes a spacer grid spring that increases the conformal contact area with a fuel rod of a nuclear fuel rod assembly. Creating a long password includes assigning portions of the long password to a plurality of media files already stored on the mobile device and concatenating each of the portions of the long password to form the long password. The gears of any one of the driving gear unit and the driven gear unit are portion gears which are gears having gear teeth on respective portions of outer peripheries thereof, the gear teeth of the portion gears are alternately disposed to each other one on another.