Evacuated containment vessel for nuclear reactor

1. A method of operating a power module including a reactor vessel and a containment vessel, wherein the containment vessel surrounds the reactor vessel and forms a containment region outside of the reactor vessel, the method comprising:

during a normal mode of operation of the power module, heating and circulating a coolant through a reactor core positioned inside of the reactor vessel; and

during an emergency mode of operation of the power module—

venting at least a portion of the coolant out of the reactor vessel and into the containment region;

stopping venting of the portion of the coolant when a pressure in the containment region exceeds a threshold value; and

flowing at least a portion of the coolant vented into the containment region from the containment vessel back into the reactor vessel through a one-way flow valve positioned between the reactor vessel and the containment vessel.

2. The method of claim 1 wherein the one-way flow valve is positioned to inhibit the coolant from flowing therethrough from the reactor vessel to the containment vessel.

3. The method off claim 1 wherein the method further comprises, during the normal mode of operation, maintaining the containment region as dry.

4. The method of claim 1 wherein the method further comprises, during the emergency mode of operation, condensing at least some of the portion of the coolant vented into the containment region on an inner surface of the containment vessel to reduce the pressure in the containment region.

5. The method of claim 1 wherein the method further comprises creating at least a partial vacuum in the containment region to draw the portion of the coolant from the reactor vessel into the containment region during the emergency mode of operation.

6. The method of claim 1 wherein the method further comprises, during the emergency mode of operation, equilibrating a level of the coolant in the reactor vessel and a level of the coolant in the containment vessel such that the level of the coolant in the containment vessel is higher than the level of the coolant in the reactor vessel.

7. The method of claim 6 wherein flowing the portion of the coolant vented into the containment region from the containment vessel back into the reactor vessel includes flowing the portion of the coolant vented into the containment region after a steady state condition is reached between the level of the coolant in the reactor vessel and the level of the coolant in the containment vessel.

8. The method of claim 1 wherein the method further comprises maintaining an at least partial vacuum in the containment region during the normal mode of operation.

9. The method of claim 1 wherein the method further comprises inhibiting heat transfer between the reactor vessel and the containment vessel during the normal mode of operation.

10. The method of claim 1 wherein venting the portion of the coolant includes venting the portion of the coolant in vapor form.

11. The method of claim 1 wherein the emergency mode of operation includes overheating of the reactor core.

12. The method of claim 1 wherein the one-way valve is a first valve, and wherein venting the portion of the coolant includes venting the portion of the coolant through a second valve.

13. The method of claim 1 wherein the first valve and the second valve are positioned on the reactor vessel, and wherein the second valve is above the first valve.

14. The method of claim 1 wherein the method further comprises:

during the normal mode of operation, inhibiting heat transfer between the reactor vessel and the containment vessel with an insulative material positioned in the containment region; and

during the emergency mode of operation, promoting heat transfer between the reactor vessel and the containment vessel with the insulative material.

15. A method of operating a power module including a reactor vessel and a containment vessel surrounding the reactor vessel, the method comprising:

heating and circulating a coolant through a reactor core positioned inside of the reactor vessel;

detecting an emergency condition; and after detecting the emergency condition—

venting at least a portion of the coolant out of the reactor vessel and into the containment vessel through a first valve positioned between the reactor vessel and the containment vessel;

stopping venting of the portion of the coolant through the first valve when a pressure in the containment vessel exceeds a threshold value; and

flowing at least a portion of the coolant vented into the containment vessel from the containment vessel back into the reactor vessel through a second valve positioned between the reactor vessel and the containment vessel, wherein the second valve is positioned to inhibit the coolant from flowing therethrough from the reactor vessel to the containment vessel.

16. The method of claim 15 wherein the first valve and the second valve are positioned on the reactor vessel, and wherein the second valve is above the first valve.

17. The method of claim 15 wherein venting the portion of the coolant includes venting the portion of the coolant in vapor form, and wherein flowing the portion of the coolant vented into the containment vessel from the containment vessel back into the reactor vessel includes flowing the portion of the coolant vented into the containment vessel in liquid form.

18. The method of claim 15 wherein the method further comprises maintaining the containment vessel as dry before detecting the emergency condition.

19. A method of operating a power module including a reactor vessel and a containment vessel that surrounds the reactor vessel, the method comprising:

during a normal mode of operation of the power module, heating and circulating a coolant through a reactor core positioned inside of the reactor vessel; and

during an emergency mode of operation of the power module—

releasing, through a first valve, at least a portion of the coolant in vapor form out of the reactor vessel and into the containment vessel until a pressure in the containment vessel at least partially equilibrates with a pressure in the reactor vessel;

stopping releasing of the portion of the coolant through the first valve when the pressure in the containment vessel exceeds a threshold value; and

flowing at least a portion of the coolant released into the containment vessel from the containment vessel back into the reactor vessel through a second valve positioned between the reactor vessel and the containment vessel, wherein the second valve is positioned to inhibit the coolant from flowing therethrough from the reactor vessel to the containment vessel.

20. The method of claim 19 wherein flowing the portion of the coolant released into the containment vessel from the containment vessel back into the reactor vessel includes flowing the portion of the coolant after the pressure in the containment vessel equilibrates with the pressure in the reactor vessel.