Patent Number: 
Section: claims

1. An apparatus comprising:an isolation valve assembly including:an isolation valve vessel including a single open end;a mounting flange sealing with the isolation valve vessel to define a sealed volume;a fluid flow line in fluid communication with the mounting flange to flow fluid through the mounting flange; anda valve disposed in the isolation valve vessel inside the sealed volume and operatively connected with the fluid flow line,wherein the fluid flow line both enters and exits the isolation valve vessel through the single open end. 2. The apparatus of claim 1, wherein the isolation valve assembly further includes a forging including the mounting flange and a second flange to which the isolation valve vessel is secured, the forging having a passageway extending between the mounting flange and the second flange through which the fluid flow line passes. 3. The apparatus of claim 1, wherein the valve is a check valve allowing flow in a first direction but not a second opposite direction within the fluid flow line. 4. The apparatus of claim 1, wherein the isolation valve assembly further includes an external isolation valve disposed outside the isolation valve vessel and outside the sealed volume and operatively connected with the fluid flow line. 5. The apparatus of claim 1, further comprising:a nuclear reactor comprising (i) a pressure vessel including a mating flange and (ii) a nuclear reactor core comprising fissile material disposed in the pressure vessel;wherein the mounting flange of the isolation valve assembly is connected with the mating flange of the pressure vessel of the nuclear reactor. 6. The apparatus of claim 5, further wherein the fluid flow line is a makeup line of a reactor coolant inventory and purification system (RCIPS) and the valve is a check valve preventing backflow of reactor coolant from the pressure vessel into the makeup line. 7. An isolation valve assembly for use with a nuclear reactor including a pressure vessel, comprising:an isolation valve vessel having a single open end with a flange;a spool piece having a first flange secured to the pressure vessel, and a second flange secured to the flange of the isolation valve vessel;a fluid flow line passing through the spool piece to conduct fluid flow into or out of the first flange wherein a portion of the fluid flow line is disposed in the isolation valve vessel; andat least one valve disposed in the isolation valve vessel and operatively connected with the fluid flow line,wherein the fluid flow line both enters and exits the isolation valve vessel through the single open end. 8. The isolation valve assembly of claim 7, wherein the at least one valve is a check valve preventing fluid flow out of the pressure vessel. 9. The isolation valve assembly of claim 8, wherein the fluid flow line is a makeup line for supplying reactor coolant to the pressure vessel and the at least one valve is a check valve preventing primary coolant from flowing out of the pressure vessel through the fluid flow line. 10. The isolation valve assembly of claim 7, wherein an end of the fluid flow line is disposed coaxially inside the spool piece. 11. The isolation valve assembly of claim 7, further comprising a redundant valve disposed outside of the isolation valve vessel and operatively connected with the fluid flow line.