Patent Number: 
Section: claims

1. A passive core decay heat transport system for water cooled reactors comprising a device in a reactor core, wherein the device comprises:at least one coolant channel containing a fuel assembly;at least one collet joint connecting a fuel in the fuel assembly to a shield plug;at least one thermo-siphon containing a liquid metal for transporting of decay heat from the fuel;at least one other thermo-siphon containing a liquid metal for transport of the decay heat from the at least one thermo-siphon; andat least one assembly of heat dissipating fins for transport of the decay heat from the at least one other thermo-siphon to an ultimate heat sink with atmosphere air;wherein thermal expansion of the liquid metal in the at least one thermo-siphon and the at least one other thermo-siphon establishes a conductive heat transfer path and a convective heat transfer path and transfers the decay heat from the fuel to the at least one thermo-siphon, and the at least one thermo-siphon transports the decay heat to the at least one other thermo-siphon and then to the at least one assembly of fins, whereby the at least one assembly of fins dissipates the decay heat by natural circulation of air within the passive core decay heat transport system into an atmospheric air. 2. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein the fuel assembly is coupled to at least one lower end fitting connecting the fuel assembly to the coolant channel. 3. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein the shield plug provides shielding from radiation and guides a flow within the at least one coolant channel. 4. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, further comprises at least one seal plug coupled to the at least one collet joint for pressure sealing a water coolant. 5. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein the at least one assembly of heat dissipating fins comprises:an isolation enclosure in a reactor closure deck;a flow guide;at least one inlet duct connected to the at least one assembly of fins;at least one outlet duct;a means to connect to a containment; andat least one air cooling duct surrounding the containment for cooling hot air from the at least one assembly of fins;wherein the conductive heat transport path and the convective heat transport path are activated by the melting of a metal to create the liquid metal, which transfers the decay heat to the ultimate heat sink in closed circuit, through the conductive heat transport path and the convective heat transport path the at least one assembly of heat dissipating fins, the flow guide, the inlet duct, the outlet duct, the containment, and the cooling duct; andwherein the at least one assembly of heat dissipating fins communicated with external air for cleansing and initiating the passive core decay heat transport system. 6. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein the at least one assembly of heat dissipating fins may have either of a rectangular, a circular or a spiral configuration. 7. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein the at least one assembly of heat dissipating may be detachable or compact staggered. 8. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein the at least one assembly of heat dissipating fins are made of a material suitable for an operating temperature of about 300° C. or more. 9. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein a metal coolant of lead is adapted to pass the decay heat from the reactor core to the ultimate heat sink. 10. A method for passive core decay heat transport in the passive core decay heat transport system for water cooled reactors of claim 1 comprising:i. melting of metal due to rise in temperature of the fuel above the melting point of the metal;ii. activation of the conductive heat transport path and the convective heat transport path due to the melting of the metal;iii. transfer of the decay heat by the conduction heat transfer path and the convective heat transfer path between the fuel assembly, the at least one thermo-siphon and the at least one other thermo-siphon;iv. transfer of the decay heat from the at least one other thermo-siphon to the at least one assembly of heat dissipating fins; andv. transfer of the decay heat by the air from the at least one assembly of heat dissipating fins to the ultimate heat sink. 11. The method for passive core decay heat transport for water cooled reactors as claimed in claim 10, wherein the metal is lead. 12. The method for passive core decay heat transport for water cooled reactors as claimed in claim 10, wherein a metal coolant passes the decay heat from the fuel to the ultimate heat sink. 13. The method for passive core decay heat transport for water cooled reactors as claimed in claim 10, wherein the method is operated passively. 14. A passive core decay heat transport device for water cooled reactors comprising:at least one lower end fitting coupled to a fuel assembly producing heat;at least one coolant channel containing the fuel assembly surrounded by primary water coolant to cool a fuel within the fuel assembly;at least one thermo-siphon containing liquid metal for transport of the heat;at least one shield plug for radiation shielding and guiding a flow within the at least one coolant channel;at least one collet joint connecting the fuel in fuel assembly to the shield plug;at least one other thermo-siphon containing liquid metal for transport of the heat; andat least one seal plug coupled to at least one assembly of heat dissipating fins, wherein the at least one seal plug comprises at least one of the at least one collet joints coupled to the at least one other thermo-siphon;wherein the fuel assembly transfers the heat to the at least one thermo-siphon using a conductive heat transfer mode and a convective heat transfer mode, and the at least one thermo-siphon transfers the heat to the at least one other thermo-siphon and then to the at least one assembly of fins, which results in cooling of the reactor core by natural circulation of air in closed circuit within the passive core decay heat transport device into an atmospheric air.