Abstract: A disk apparatus includes a disk holder for holding a disk, and the disk holder is reciprocatively movable between a loading position and an unloading position. The disk apparatus further includes a motor for driving the disk at the loading position for reading or writing purposes, a power transmission mechanism for converting the rotation of the shaft of the motor into a reciprocative motion and for transmitting the reciprocative motion to the disk holder, and a switching mechanism for switching the power transmission mechanism to an inoperative state so as to prevent the power of the motor from being transmitted from the motor to the disk holder when the motor is operating to rotate the disk for reading or writing purposes.

Abstract: A reactor system of a boiling water type atomic power plant including a reactor pressure vessel, a primary containment vessel containing the reactor pressure vessel, a main turbine, a main steam piping extending through the primary containment vessel between the reactor pressure vessel and the main turbine, and inside and outside main steam isolation valves provided on the main steam piping inside and outside the primary containment vessel, respectively. A closure valve is provided on the main steam piping at a position near the primary containment vessel and is adapted to quickly close in less than 3 seconds upon a break accident of the main steam piping. A volume of the reactor pressure vessel allotted for accommodating steam is correspondingly enlarged to allow the closure valve to quickly close upon a break accident of the main steam piping.