Pressure suppression system

A method for suppressing pressure inside a drywell of a nuclear reactor having a containment vessel, a reactor pressure vessel surrounded by said containment vessel with said drywell therebetween, said drywell being filled during normal operation with non-condensable gas, a nuclear fuel core arranged inside said reactor pressure vessel, and a gravity-driven cooling system ("GDCS") pool containing water having an elevation which is higher than the elevation of said fuel core, comprising the steps of:

• draining GDCS pool water via a drainage path into said reactor pressure vessel by gravity in response to an emergency condition which results in steam being released from said reactor pressure vessel into said drywell;
• channeling released steam and non-condensable gas via a flow path from said drywell into a GDCS plenum above residual water in said drained GDCS pool;
• and
• condensing steam inside said GDCS plenum for drawing in additional steam and non-condensable gas from said drywell and thereby preventing escape of non-condensable gas from said GDCS plenum.

In a passive emergency cooling system of a boiling water reactor having a primary containment vessel, a reactor pressure vessel surrounded by said primary containment vessel with a drywell therebetween, a nuclear fuel core arranged inside said reactor pressure vessel, and a suppression pool containing water located inside said primary containment vessel and outside said reactor pressure vessel, said passive emergency cooling system comprising:

• a gravity-driven cooling system pool containing water having an elevation which is higher than the elevation of said fuel core, a drainage path by which water can flow by gravity from said gravity-driven cooling system pool to said reactor pressure vessel, valve means for opening said flow path from said gravity-driven cooling system pool to said reactor pressure vessel to allow gravity-driven water flow in response to an emergency condition, a condensate inlet flow path for receiving condensate from outside said gravity-driven cooling system pool, a first loop seal in flow communication with said condensate inlet flow path, and a steam inlet for channeling steam from said drywell into a gravity-driven cooling system plenum above the water contained by said gravity-driven cooling system pool;
• and
• a condenser pool containing water, a condenser submerged in said water in said condenser pool, a condenser inlet flow path for coupling steam from said drywell into said condenser, a first condenser outlet flow path for coupling non-condensable gases from said condenser into said suppression pool, and a second condenser outlet flow path for coupling condensate from said condenser into said condensate inlet flow path in said gravity-driven cooling system pool,
• the improvement wherein means for condensing steam are arranged inside said gravity-driven cooling system pool, said steam condensing means receiving condensate via said condensate inlet flow path and said first loop seal, and wherein said drainage path comprises a second loop seal in flow communication with water in said gravity-driven cooling system for preventing the flow of non-condensable gas from said gravity-driven cooling system plenum to said reactor pressure vessel.