Patent Number: 
Section: claims

1. A system comprising:at least one coolant pump configured to pump coolant water into or out of an associated nuclear reactor vessel;at least one external coolant conduit that is external to the nuclear reactor vessel connecting said at least one coolant pump with the associated nuclear reactor vessel; anda vessel isolation valve having a mounting flange configured to connect with a mating flange of a vessel penetration through an outer wall of the associated nuclear reactor vessel, the vessel isolation valve fluidly connecting with the at least one external coolant conduit, the vessel isolation valve configured to block outward flow from the pressure vessel when a pressure differential across the valve exceeds prescribed criteria;wherein the vessel isolation valve further includes:a valve seat defined in the mounting flange,a moveable valve member movable between an open position permitting flow through the vessel isolation valve and a closed position seating against the valve seat to block flow through the vessel isolation valve,a biasing member that biases the valve member towards the open position, andan actuator operatively coupled to the movable valve member for maintaining the valve member in the closed position. 2. The system of claim 1, wherein the valve member of the vessel isolation valve includes a piston adapted to seal against the valve seat. 3. The system of claim 2, wherein the vessel isolation valve further comprises:a rod connected to the piston and protruding axially away from the mounting flange along a longitudinal center axis of the biasing member, and wherein the biasing member comprises a spring operatively engaged with the rod. 4. The system of claim 3, wherein the spring is at least partially surrounded by a spring cover removably secured to the vessel isolation valve. 5. The system of claim 1, wherein the movable valve member is entirely contained in one or more of (i) the associated nuclear reactor vessel, (ii) the outer wall of the associated nuclear reactor vessel, and (iii) a flange assembly including the mating flange welded to the outer wall and the mounting flange of the vessel isolation valve. 6. A system comprising:at least one coolant pump configured to pump coolant water into or out of an associated nuclear reactor vessel;at least one external coolant conduit that is external to the nuclear reactor vessel connecting said at least one coolant pump with the associated nuclear reactor vessel; anda vessel isolation valve having a mounting flange configured to connect with a mating flange of a vessel penetration through an outer wall of the associated nuclear reactor vessel, the vessel isolation valve fluidly connecting with the at least one external coolant conduit, the vessel isolation valve configured to block outward flow from the pressure vessel when a pressure differential across the valve exceeds prescribed criteria;wherein the vessel isolation valve further includes:a valve body defining a central bore,a valve seat formed in the central bore of the valve body,a moveable valve member movable between an open position permitting flow through the vessel isolation valve and a closed position seating against the valve seat to block flow through the vessel isolation valve, andwherein the valve seat is coaxially aligned with the mounting flange so as to be disposed within a vessel penetration valve assembly formed by the mounting flange and the mating flange. 7. The system of claim 6, wherein the vessel isolation valve further includes a biasing member that biases the valve member towards the open position. 8. The system of claim 7, wherein the valve member of the vessel isolation valve includes a piston adapted to seal against the valve seat. 9. The system of claim 8, wherein the vessel isolation valve further comprises:a rod connected to the piston and protruding axially away from the mounting flange along a longitudinal counter axis of the biasing member, and wherein the biasing member comprises a spring operatively engaged with the rod. 10. The system of claim 9, wherein the spring is at least partially surrounded by a spring cover removably secured to the vessel isolation valve. 11. The system of claim 6, wherein the movable valve member is entirely contained in one or more of (i) the associated nuclear reactor vessel, (ii) the outer wall of the associated nuclear reactor vessel, and (iii) the vessel penetration valve assembly. 12. The system of claim 6, wherein the vessel isolation valve further includes an actuator operatively coupled to the movable valve member for maintaining the valve member in the closed position.