A shutter assembly for a reactor includes a cylindrical shutter for selectively closing a passthrough opening of the reactor, the shutter forming a closed loop and including an internal cavity adapted to receive a cooling fluid, tubing connected with the cylindrical shutter for supplying the cooling fluid to the internal cavity, and an actuator connected with the tubing for moving the tubing and the cylindrical shutter. The cylindrical shutter is movable between a first substantially closed position and a second substantially open position.