Patent Number: 053295641
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The drawing of FIG. 1 illustrates a typical open cycle nuclear reactor and coolant system. Coolant tank 10 contains pressurized coolant that is released to coolant pump 12 through coolant line 14. Coolant pump 12 directs coolant through coolant line 14 to nuclear reactor 16. In an open cycle reactor designed for use in outer space the coolant exits reactor 16 through exhaust line 18 and may be used for providing propulsive thrust and/or providing power in conjunction with dynamic conversion devices. When reactor 16 and coolant pump 12 are shut down, it is necessary to remove decay heat from reactor 16. This is accomplished by incorporating passive cooling system 20 into the nuclear reactor coolant system. Passive cooling system 20 is generally comprised of coolant tanks 22, check valves 24, and flow control means 26. Coolant tanks 22 are in fluid communication with coolant line 14 by means of inlet lines 28 and exhaust lines 30. Check valves 24 positioned in inlet lines 28 allow coolant to flow from coolant line 14 into coolant tanks 22 while preventing coolant flow from coolant tanks 22 into inlet lines 28. Flow control means 26 is positioned in exhaust lines 30 to provide a predetermined coolant flow rate from each coolant tank 22 into exhaust lines 30, coolant line 14, and to reactor 16. Each flow control means 26 provides for a different rate of coolant flow. The flow rate of each flow control means 26 is determined by the known decay heat rate of reactor 16. This allows the coolant flow rate from tanks 22 to match the decay heat rate of the reactor to prevent under or over cooling after reactor 16 is shutdown and coolant pump 12 is inoperative. Each flow control means 26 may be a control valve or a fixed orifice. During normal operations of reactor 16, coolant from coolant tank 10 is received by coolant pump 12. Coolant pump 12 forces the coolant through coolant line 14 to reactor 16 and into inlet lines 28. Check valves 24 allow coolant to flow into coolant tanks 22 until the coolant pressure therein equals the discharge pressure of coolant pump 12. Check valves 24 also prevent the back flow of coolant through inlet lines 28 when the coolant pump discharge pressure decreases. When reactor 16 is shut down, coolant pump 12 is also shut down as a normal function of system operation. Coolant pressure in coolant line 14 then drops to a level below that in coolant tanks 22. At that time, flow control means 26 allow flow of coolant from coolant tanks 22 into coolant line 14. Due to the pressure from coolant tanks 22, the coolant travels to reactor 16, removes decay heat, and exits through exhaust line 18. Each flow control means 26 provides for a different rate of flow. The flow rate of each control means 26 is determined in relation to the known decay heat rate of reactor 16 and the volume and number of coolant tanks 22 to be used. In this manner, the initial coolant flow from all of coolant tanks 22 provides sufficient coolant for the higher level of decay heat immediately after reactor shutdown. As the pressure in coolant tanks 22 is reduced, or the tanks successively empty, the reduced coolant flow is sufficient for lower levels of heat removal required during the later stages of decay heat removal. Thus, the decay heat rate of the reactor is matched to prevent under or over cooling and to provide the proper rate of cooling. This provides a passive cooling system for removal of decay heat that is automatically filled with coolant during normal reactor operations and begins operation at reactor and coolant pump shutdown without the need for complicated controls that may easily malfunction. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.