Patent Number: 
Section: claims

1. A power module assembly comprising:a containment vessel;a reactor vessel housed in the containment vessel, wherein the reactor vessel is configured to release coolant into a containment region located between the reactor vessel and the containment vessel, and wherein the containment vessel is configured to prohibit the released coolant from escaping out of the containment vessel; anda thermal insulation of the reactor vessel including the containment region located between the reactor vessel and the containment vessel, wherein the containment region comprises a partial vacuum that substantially surrounds the reactor vessel and is maintained at a below atmospheric pressure of less than 300 mmHG absolute. 2. The power module assembly of claim 1, wherein the reactor vessel is configured to release coolant into the containment region in response to a high-pressure event, wherein an entirety of the containment region is maintained at the below atmospheric pressure prior to the high-pressure event, and wherein substantially all gases are evacuated from the containment region during normal operation of the power module assembly. 3. The power module assembly of claim 2, wherein the evacuated gases comprise non-condensable gases, and wherein the containment region remains substantially evacuated of all non-condensable gases during an emergency operation comprising the high-pressure event, when the coolant is released into the containment region. 4. The power module assembly of claim 2, wherein the evacuated gases comprise oxygen, and wherein any hydrogen that is released together with the coolant is released at a level that maintains an oxygen-hydrogen mixture within the containment vessel at a non-combustible level without using a hydrogen recombiner. 5. The power module assembly of claim 1, wherein the reactor vessel is configured to release coolant into the containment region in response to a high-pressure event, and wherein the below atmospheric pressure prohibits substantially all convective heat transfer between the reactor vessel and the containment vessel during normal operation of the power module assembly prior to the high-pressure event. 6. The power module assembly of claim 1, wherein the reactor vessel is configured to release coolant into the containment region in response to a high-pressure event, and wherein the containment region remains substantially dry during normal operation of the power module assembly prior to the high-pressure event. 7. The power module assembly of claim 1, wherein the reactor vessel is configured to release coolant into the containment region in response to a high-pressure event, and wherein an outer surface of the reactor vessel is substantially surrounded by the below atmospheric pressure during normal operation of the power module assembly prior to the high-pressure event. 8. The power module assembly of claim 1, further comprising a flow limiter configured to controllably vent the released coolant as steam into the containment region during an emergency operation comprising a high-pressure event. 9. The power module assembly of claim 8, wherein a condensation of the steam on an interior wall of the containment vessel reduces pressure in the containment vessel at approximately the same rate that the vented steam adds pressure to the containment vessel. 10. The power module assembly of claim 8, wherein the steam is released into the containment vessel to remove a decay heat of a reactor core primarily through condensation of the steam on an inner surface of the containment vessel. 11. The power module assembly of claim 1, wherein the reactor vessel is configured to release coolant into the containment region in response to a high-pressure event, wherein an inner surface of the containment vessel substantially surrounds the reactor vessel, and wherein the inner surface of the containment vessel is substantially dry during normal operation of the power module assembly prior to the high-pressure event. 12. The power module assembly of claim 1, wherein the containment vessel comprises an inner wall, wherein the reactor vessel comprises an outer wall, and wherein the containment region is located between the inner wall and the outer wall. 13. The power module assembly of claim 1, wherein the reactor vessel is configured to release coolant into the containment region in response to a high-pressure event, and wherein all of the containment region is maintained at the below atmospheric pressure prior to the high-pressure event. 14. The power module assembly of claim 1, wherein the reactor vessel is configured to release coolant into the containment region in response to a high-pressure event, wherein the partial vacuum substantially surrounds the reactor vessel at a below atmospheric pressure of less than 300 mmHG absolute prior to the high-pressure event, and wherein the containment vessel prohibits the released coolant from escaping out of the containment vessel in response to the high-pressure event. 15. A power module assembly comprising:a containment vessel;a reactor vessel housed in the containment vessel, wherein the reactor vessel is configured to release coolant into a containment region, and wherein the containment vessel is configured to prohibit a release of the coolant out of the containment vessel; anda thermal insulation of the reactor vessel including the containment region located between the reactor vessel and the containment vessel, wherein the containment region comprises a partial vacuum that substantially surrounds the reactor vessel and is maintained at a below atmospheric pressure, and wherein the below atmospheric pressure prohibits substantially all convective heat transfer between the reactor vessel and the containment vessel. 16. The power module assembly of claim 15, wherein the below atmospheric pressure is less than 300 mmHG absolute. 17. The power module assembly of claim 15, wherein the containment vessel is surrounded by a heat sink. 18. The power module assembly of claim 17, wherein the heat sink comprises water or gas. 19. The power module assembly of claim 17, wherein the heat sink comprises rock, soil, or other solid material. 20. The power module assembly of claim 15, wherein the partial vacuum is maintained at the below atmospheric pressure, which is less than 300 mmHG absolute, prior to a high-pressure event and during normal operation of the power module assembly, and wherein the reactor vessel is configured to release coolant into the containment region during an emergency operation of the power module assembly comprising the high-pressure event. 21. The power module assembly of claim 20, wherein the containment vessel is configured to prohibit a release of the coolant out of the containment vessel during the emergency operation. 22. The power module assembly of claim 20, wherein the containment region comprises a first containment region and a second containment region, wherein the first containment region is maintained at atmospheric pressure, and wherein the second containment region is maintained at the below atmospheric pressure. 23. The power module assembly of claim 22, wherein the coolant is released as steam into the first containment region during the emergency operation, and wherein the steam condenses as liquid coolant in the containment vessel. 24. The power module assembly of claim 23, further comprising one or more valves connecting the first containment region to the second containment region, and wherein the one or more valves are operatively configured to transfer the liquid coolant from the first containment region to the second containment region. 25. The power module assembly of claim 23, wherein the reactor vessel is insulated by conventional thermal insulation in the first containment region, and wherein the reactor vessel is insulated by a reflective insulation in the second containment region. 26. A power module assembly, comprising:a thermal insulation including a containment region, wherein the containment region comprises a partial vacuum;means for releasing coolant into the containment region, wherein a reactor core is housed in the means for releasing; andcontainment means for maintaining the partial vacuum at less than 300 mmHG absolute, wherein the containment region is located between the means for releasing and the containment means, wherein the partial vacuum substantially surrounds the means for releasing, and wherein the containment means is configured to completely retain the released coolant within the containment means. 27. The power module assembly of claim 26, wherein the means for releasing coolant comprises a reactor vessel, and wherein the containment region is bordered by an inner wall of the containment means and an outer wall of the reactor vessel. 28. The power module assembly of claim 27, wherein the partial vacuum prohibits substantially all convective heat transfer between the outer wall of the reactor vessel and the inner wall of the containment vessel. 29. The power module assembly of claim 26, wherein the means for releasing comprises means for releasing the coolant into the containment region during an emergency operation of the power module assembly comprising a high-pressure event, and wherein the containment means comprises containment means for maintaining the partial vacuum at less than 300 mmHG absolute during a normal operation of the power module assembly prior to the high-pressure event. 30. The power module assembly of claim 26, wherein the means for releasing comprises means for releasing the coolant into the containment region during a high-pressure event, wherein the partial vacuum substantially surrounds the means for releasing prior to the high-pressure event, and wherein the containment means is configured to completely retain the released coolant within the containment means during the high-pressure event.