Patent Number: 
Section: claims

1. A method comprising:maintaining a containment region at a below atmospheric pressure prior to a high pressure event, wherein the below atmospheric pressure is less than 300 mmHG absolute;identifying the high pressure event for a reactor vessel;releasing coolant into the containment region located between a containment vessel and the reactor vessel to remove decay heat from the reactor vessel, wherein the reactor vessel is substantially surrounded by the containment region;increasing a pressure within the containment region in response to releasing the coolant until the pressure reaches an upper pressure limit; anddecreasing the pressure through condensation until the pressure reaches a lower pressure limit, wherein the pressure is cyclically increased and decreased by alternatively releasing and prohibiting the release of coolant into the containment region. 2. The method according to claim 1, further comprising:condensing the coolant on an inner wall of the containment vessel during an over-pressurization or over-heating event. 3. The method according to claim 1, wherein the below atmospheric pressure prohibits substantially all convective heat transfer between the reactor vessel and the containment vessel prior to releasing the coolant. 4. The method according to claim 1, wherein the containment region remains substantially evacuated of all non-condensable gases both prior to and after releasing the coolant. 5. The method according to claim 1, wherein the containment region is substantially dry prior to the high pressure event. 6. The method of claim 1, wherein an outer surface of the reactor vessel is substantially surrounded by the below atmospheric pressure prior to releasing the coolant. 7. The method of claim 1, wherein the containment region remains substantially evacuated of air and hydrogen gases during normal operation of the reactor module to substantially eliminate all convective heat transfer between the reactor vessel and the containment vessel. 8. The method of claim 1, wherein a release valve mounted to the reactor vessel releases the coolant into the containment region during an emergency condition, and wherein a mixture of hydrogen and oxygen in the containment region is maintained at below combustible limits during the emergency condition without the use of a hydrogen recombiner. 9. An apparatus, comprising:means for maintaining a containment region at a below atmospheric pressure prior to a high pressure event, wherein the below atmospheric pressure is less than 300 mmHG absolute;means for identifying the high pressure event for a reactor vessel; andmeans for releasing coolant from the reactor vessel into the containment region located between a containment vessel and the reactor vessel to remove decay heat from the reactor vessel, wherein the reactor vessel is substantially surrounded by the containment region, wherein a reactor core is submerged in the coolant, and wherein the means for releasing comprises means for controllably releasing the coolant as steam into the containment region when the reactor core becomes over-heated or over-pressurized. 10. The apparatus according to claim 9, wherein a condensation of the steam on an interior wall of the containment vessel reduces pressure in the containment region at approximately the same rate that the released steam adds pressure to the containment region. 11. The apparatus according to claim 9, wherein the steam is released into the containment region to remove a decay heat of the reactor core primarily through condensation of the steam on an inner surface of the containment vessel. 12. The apparatus according to claim 9, wherein the containment region remains substantially evacuated of all non-condensable gases prior to releasing the coolant into the containment region. 13. The apparatus according to claim 9, wherein any hydrogen that is released together with the steam is released at a level that maintains an oxygen-hydrogen mixture within the containment region at a non-combustible level without using a hydrogen recombiner. 14. The apparatus according to claim 9, 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 prior to releasing the coolant. 15. The apparatus of claim 9, wherein controllably releasing the coolant comprises increasing a pressure in the containment region, wherein the pressure in the containment region is decreased through condensation of the steam in the containment region, and wherein the pressure in the containment region is cyclically increased to an upper pressure limit and decreased to a lower pressure limit by alternatively releasing and prohibiting the release of the steam into the containment region. 16. A method, comprising:maintaining a containment region at a below atmospheric pressure prior to a high pressure event, wherein the below atmospheric pressure prohibits substantially all convective heat transfer between a reactor vessel and a containment vessel which substantially surrounds the reactor vessel;monitoring a pressure associated with the reactor vessel to identify the high pressure event; andin response to identifying the high pressure event, controllably releasing coolant as steam into the containment region located between the containment vessel and the reactor vessel, wherein a reactor core is submerged in the coolant, and wherein the coolant is controllably released as steam into the containment region when the reactor core becomes over-heated or over-pressurized. 17. The method of claim 16, wherein maintaining the containment region at a below atmospheric pressure comprises maintaining the containment region at a pressure that is less than 300 mmHG absolute. 18. The method of claim 16, wherein the steam is released from the reactor vessel into the containment region to remove a decay heat of the reactor core primarily through condensation of the steam on an inner surface of the containment vessel. 19. The method of claim 16, wherein controllably releasing the coolant comprises increasing a pressure in the containment region, wherein the pressure in the containment region is decreased through condensation of the steam in the containment vessel, and wherein the pressure in the containment region is cyclically increased to an upper pressure limit and decreased to a lower pressure limit by alternatively releasing and prohibiting the release of the steam into the containment region. 20. The method of claim 16, wherein maintaining the containment region at a below atmospheric pressure comprises evacuating substantially all non-condensable gases from the containment region prior to identifying the high pressure event. 21. An apparatus, comprising:means for maintaining a containment region at a below atmospheric pressure prior to a high pressure event, wherein the below atmospheric pressure prohibits substantially all convective heat transfer between a reactor vessel and a containment vessel which substantially surrounds the reactor vessel; andin response to identifying the high pressure event, means for controllably releasing coolant as steam into the containment region located between the containment vessel and the reactor vessel to remove decay heat from the reactor vessel, wherein the means for controllably releasing the coolant comprises means for increasing a pressure within the containment region, wherein the pressure is decreased through condensation of the steam in the containment region, and wherein the pressure in the containment region is cyclically increased to an upper pressure limit and decreased to a lower pressure limit by alternatively releasing and prohibiting the release of the steam into the containment region. 22. The apparatus of claim 21, wherein the means for maintaining comprises means for maintaining the containment region at a pressure that is less than 300 mmHG absolute. 23. The apparatus of claim 21, wherein the means for maintaining comprises means for evacuating substantially all air and hydrogen gases from the containment region prior to releasing the coolant.