Patent Number: 
Section: claims

1. An apparatus comprising:a pressurized water reactor (PWR) comprising a pressure vessel containing a nuclear reactor core comprising fissile material;a central riser disposed inside the pressure vessel and defining a coolant circulation path in which coolant water heated by the nuclear reactor core flows upward inside the central riser, exits a top opening of the central riser, and flows downward in a downcomer annulus defined between the central riser and the pressure vessel to return to the nuclear reactor core;a radiological containment structure inside of which the PWR is disposed;an emergency core cooling system configured to drain water from a body of water through an injection line into the pressure vessel in response to a vessel penetration break at the top of the pressure vessel that depressurizes the pressure vessel; andan extension of the injection line disposed inside the pressure vessel and passing through the central riser, the extension configured to operate concurrently with the emergency core cooling system to suppress flow of liquid water from the pressure vessel out the vessel penetration break at the top of the pressure vessel. 2. The apparatus of claim 1 wherein the extension of the injection line includes a downwardly oriented outlet spigot disposed inside the central riser. 3. The apparatus of claim 1 wherein the body of water comprises a refueling water storage tank (RWST) disposed with the PWR in the radiological containment. 4. The apparatus of claim 3 wherein the emergency core cooling system further includes:a pressurized water injection tank configured to inject pressurized water into the pressure vessel during depressurization of the pressure vessel;wherein the injection line is configured to drain water from the RWST into the pressure vessel after the depressurization of the pressure vessel. 5. The apparatus of claim 1 wherein the PWR further comprises an integral pressurizer defining a pressurizer volume at the top of the pressure vessel, the integral pressurizer including pressure control elements operable to control pressure in the pressurizer volume. 6. The apparatus of claim 1 further comprising:openings in a lower portion of the central riser arranged to shunt a portion of the upward flow in the central riser into a lower portion of the downcomer annulus. 7. The apparatus of claim 1 wherein:an integral pressurizer defining a pressurizer volume at the top of the pressure vessel and including pressure control elements operable to control pressure in the pressurizer volume; anda surge line configured to provide fluid communication between the pressurizer volume at the top of the pressure vessel and the remainder of the pressure vessel, the surge line configured to direct water outboard toward the downcomer annulus.