Method of introducing atmospheric air in a central control room upon accidents

Purpose: To decrease the danger of radiation exposure to operators in a central control room by introducing external airs through an air intake port where the radioactivity level is the lowest depending on the information from radiation monitors and CO2 densitometers in the central control room. Method: After the occurrence of accident, the control system judges whether it is necessary or not to introduce external airs to the central control room depending on the signals from CO2 densitometers and, if it is not, air valves are kept closed. While on the other hand, if CO2 density is high thus requiring introduction of external airs, air intake ports at the lowest radioactivity level is selected based on the signals from radiation monitors and external airs are introduced to the central control room by sending ''open'' signal to the air valve disposed to a duct in communication with the air intake port, as well as by sending operation signals to a fan. This enables to introduce external airs at sufficiently low radioactivity level by a required amount to the central control room upon accident thereby decreasing the exposure danger to the operators caused by the introduction of the external airs. (Kawakami, Y.)