A passive residual heat removal system, comprising: a reactor pressure vessel; a nuclear reactor core placed in the reactor pressure vessel; a primary containment vessel including a drywell to surround the reactor pressure vessel, and a suppression chamber internally provided with a suppression pool; a vent line connecting the drywell and the suppression pool, the vent line being fitted with a plurality of openings in the suppression pool; a coolant pool filled with a coolant and provided above the primary containment vessel; a heat exchanger placed under the coolant in the coolant pool; a steam suction line connecting the drywell and the heat exchanger; a condensate storage tank disposed below the heat exchanger and above an upper end of the nuclear reactor core; a first condensate discharge line connecting the condensate storage tank and the heat changer; a non-condensate gas discharge line connected at a first end thereof to an upper section of the condensate storage tank and at a second end thereof to the suppression pool, the second end of the non-condensate gas discharge line being open at a position higher than a highest opening of the vent line in the suppression pool; and a second condensate discharge line connected at a first end thereof to a position below that section of the condensate storage tank to which the first end of the non-condensate gas discharge line is connected, and at a second end thereof to the suppression pool, the second end of the second condensate gas discharge line being open at a position lower than a lowest opening of the vent line in the suppression pool; characterized in that a condensate return line connected at a first end thereof to a position below that section of the condensate storage tank to which the first end of the second condensate discharge line (8, 9) is connected, and at a second end thereof to a side portion of the reactor pressure vessel, the side portion being above the upper end of the core, and in that the open end of the second condensate discharge line, positioned in the suppression pool, is branched into a plurality of horizontal lines, with condensate discharge ports being formed at distal ends of the branched horizontal lines. a reactor pressure vessel; a nuclear reactor core placed in the reactor pressure vessel; a primary containment vessel including a drywell to surround the reactor pressure vessel, and a suppression chamber internally provided with a suppression pool; a vent line connecting the drywell and the suppression pool, the vent line being fitted with a plurality of openings in the suppression pool; a coolant pool filled with a coolant and provided above the primary containment vessel; a heat exchanger placed under the coolant in the coolant pool; a steam suction line connecting the drywell and the heat exchanger; a condensate storage tank disposed below the heat exchanger and above an upper end of the nuclear reactor core; a first condensate discharge line connecting the condensate storage tank and the heat changer; a non-condensate gas discharge line connected at a first end thereof to an upper section of the condensate storage tank and at a second end thereof to the suppression pool, the second end of the non-condensate gas discharge line being open at a position higher than a highest opening of the vent line in the suppression pool; and a second condensate discharge line connected at a first end thereof to a position below that section of the condensate storage tank to which the first end of the non-condensate gas discharge line is connected, and at a second end thereof to the suppression pool, the second end of the second condensate gas discharge line being open at a position lower than a lowest opening of the vent line in the suppression pool; a condensate return line connected at a first end thereof to a position below that section of the condensate storage tank to which the first end of the second condensate discharge line (8, 9) is connected, and at a second end thereof to a side portion of the reactor pressure vessel, the side portion being above the upper end of the core, and in that the open end of the second condensate discharge line, positioned in the suppression pool, is branched into a plurality of horizontal lines, with condensate discharge ports being formed at distal ends of the branched horizontal lines.