Air ventilation facility for closed chamber and aid system upon stoppage of power supply

The present invention concerns a ventilation facility for a closed chamber and an aid therefor upon stoppage of power supply in a spent fuel reprocessing plant, and provides a method of maintaining depressurized atmosphere by evacuating the closed chamber till starting of the power supply of an emergency power generating facility. Namely, the facility comprises an exhaustion fan, a fly wheel for continuously rotating the exhaustion fan by inertia upon stoppage of power supply, and an emergency power generation facility connected to a source for rotating the exhaustion fan and actuating upon stoppage of power supply. With such a constitution, air in the chamber is continuously sucked by the exhaustion fan even upon stoppage of power supply, and the depressurized atmosphere in the closed chamber can be maintained until the start of the power supply by the emergency power generation facility. In this case, since the suction of the exhaustion fan is decreased moderately, change of the order of the gas pressure in a gas sucking system or in various kinds of facilities connected therewith can be suppressed, to prevent occurrence of back flow and mixing phenomenon of gases. (I.S.)