Patent Number: 
Section: claims

1. An apparatus for use with a reactor pressure vessel defining an internal volume filled with primary coolant, comprising:an isolation valve in fluid communication with the internal volume of the pressure vessel, including:a mounting flange configured to connect with a mating flange of the pressure vessel,a valve body defining a central bore having an axis orthogonal to a longitudinal axis of the pressure vessel;a valve seat formed in the central bore of the valve body, anda valve member movable between an open position permitting flow through the isolation valve and a closed position in which the valve member seals against the valve seat to block flow through the isolation valve,wherein the valve seat is aligned with the mounting flange along the bore axis and along a radius of the central bore with a vessel penetration flange assembly formed by the mounting flange and the mating flange when the mounting flange is connected with the mating flange of the pressure vessel. 2. The apparatus of claim 1, wherein the isolation valve further comprises:a biasing member operatively connected to the valve member that biases the valve member towards the open position. 3. The apparatus of claim 2, wherein the biasing member is configured to provide bias effective to keep the valve member in the open position except when a differential fluid pressure across the isolation valve and directed outward from the pressure vessel exceeds a threshold pressure. 4. The apparatus of claim 1, wherein the mounting flange of the isolation valve includes a portion adapted to be received in a bore in the associated reactor vessel. 5. The apparatus of claim 1,wherein the mounting flange of the isolation valve is connected with the mating flange of the pressure vessel. 6. The apparatus of claim 1, further comprising:a nuclear reactor comprising (i) the pressure vessel including the mating flange and (ii) a nuclear reactor core comprising fissile material disposed in the pressure vessel;wherein the mounting flange of the isolation valve is connected with the mating flange of the pressure vessel of the nuclear reactor. 7. The apparatus of claim 6, further comprising:a coolant makeup line connected with the mating flange of the pressure vessel;wherein the isolation valve is interposed between the coolant makeup line and the mating flange of the pressure vessel. 8. The apparatus of claim 6, further comprising:a coolant letdown line connected with the mating flange of the pressure vessel;wherein the isolation valve is interposed between the coolant letdown line and the mating flange of the pressure vessel.