Patent Number: 
Section: claims

1. A boiling water nuclear reactor system, comprising:a reactor pressure vessel;a reactor core disposed in the reactor pressure vessel;a core shroud surrounding the reactor core;a downcomer region disposed between an inner surface of the reactor pressure vessel and the core shroud;a steam line connected to an upper end of the reactor pressure vessel; andan isolation condenser system receives steam from the reactor pressure vessel and includes a condensate return line that is directly connected to the core shroud and selectively returns condensate directly inside the core shroud above the reactor core into one or both of an upper plenum or chimney region of the core shroud, the condensate return line includes a valve that opens flow through the condensate return line during a reactor shutdown. 2. The boiling water nuclear reactor system according to claim 1, wherein the condensate return line further includes a split portion that returns condensate inside the downcomer region. 3. The boiling water nuclear reactor system according to claim 1, further comprising:a turbine receiving steam from the reactor pressure vessel; anda main condenser system receiving the steam from the turbine and connected to the reactor pressure vessel by a feedwater return line for returning condensate from the main condenser system. 4. The boiling water nuclear reactor system according to claim 3, wherein the feedwater return line selectively returns condensate inside the core shroud above the reactor core into one or both of an upper plenum or chimney region of the core shroud. 5. The boiling water nuclear reactor system according to claim 4, wherein the feedwater return line includes a first split portion that returns condensate inside the downcomer. 6. The boiling water nuclear reactor system according to claim 3, wherein the feedwater return line returns condensate inside the downcomer. 7. A boiling water nuclear reactor system, comprising:a reactor pressure vessel;a reactor core disposed in the reactor pressure vessel;a core shroud surrounding the reactor core;a downcomer region disposed between an inner surface of the reactor pressure vessel and the core shroud;a steam line connected to an upper end of the reactor pressure vessel;a turbine receiving steam from the reactor pressure vessel;a main condenser system receiving the steam from the turbine and connected to the reactor pressure vessel by a feedwater return line for returning condensate from the main condenser system, the feedwater return line selectively returning condensate inside the core shroud above the reactor core into one or both of an upper plenum or chimney region of the core shroud, andan isolation condenser system receives steam from the reactor pressure vessel and includes a condensate return line that is directly connected to the core shroud and selectively returns condensate directly inside the core shroud above the reactor core into one or both of an upper plenum or chimney region of the core shroud, the condensate return line includes a valve that opens flow through the condensate return line during a reactor shutdown. 8. The boiling water nuclear reactor system according to claim 7, wherein the feedwater return line includes a first split portion that returns condensate inside the downcomer. 9. The boiling water nuclear reactor system according to claim 7, wherein the condensate return line further includes a split portion that returns condensate inside the downcomer region.