Patent Number: 
Section: claims

1. An emergency core cooling system, comprising:at least one direct vessel injection nozzle, arranged without protrusion towards a core barrel arranged in a reactor vessel, that injects a jet of emergency core cooling water toward the core barrel arranged in the reactor vessel, wherein the reactor vessel comprises a cooling system having a plurality of cold legs and hot legs installed thereon; andat least one injection extension duct arranged on an outer surface of the core barrel facing a corresponding direct vessel injection nozzle, the at least one injection extension duct being mechanically disconnected from the corresponding direct vessel injection nozzle and protruding from the core barrel toward the reactor vessel within a predetermined distance that is less than a hot leg surface defined by a hot leg inner diameter and less than an upper alignment key portion surface defined by a minimum inner diameter of an upper alignment key portion of the reactor vessel, wherein the at least one injection extension duct includes unperforated lateral faces inclined in a transverse direction at an angle of about 45° with reference to an outer surface of the core barrel, at least one air vent configured to permit gas discharge when the reactor vessel is filled with cooling water, and an emergency core cooling water intake port, arranged without protrusion towards the corresponding direct vessel injection nozzle, passing through an outer surface of the at least one injection extension duct, wherein the emergency core cooling water intake port includes a diameter about twice an inner diameter of the corresponding direct vessel injection nozzle and is axially aligned along the corresponding direct vessel injection nozzle such that the jet of emergency core cooling water injected from the corresponding direct vessel injection nozzle flows into the corresponding injection extension duct. 2. The emergency core cooling system as set forth in claim 1, wherein the at least one injection extension duct is open at the lowest portion thereof, and is closed at the highest portion thereof. 3. The emergency core cooling system as set forth in claim 1, wherein the at least one injection extension duct protrudes from the core barrel toward the reactor vessel within a predetermined distance, which ranges from about 3/25 to about 7/25 of the width of a diametrical gap of a downcomer, which is an annular space formed between the reactor vessel and the core barrel. 4. The emergency core cooling system as set forth in claim 1, wherein the at least one injection extension duct installed on the core barrel has a length originating from the emergency core cooling water intake port facing the at least one direct vessel injection nozzle of the reactor vessel, and extending to a lower portion of a downcomer below positions of the plurality of cold legs and hot legs along an outer surface of the core barrel. 5. The emergency core cooling system as set forth in claim 4, wherein the at least one injection extension duct has an outlet, a position of which extends toward the lower portion of the downcomer from a central axis of each cold leg within a range from about two to four times the inner diameter of each cold leg.