Zamak stabilization of spent sodium-cooled reactor fuel assemblies
Methods and systems for stabilizing spent fuel assemblies from sodium-cooled nuclear reactors using Zamak are described herein. It has been determined that there is a synergism between Zamak and sodium that allows Zamak to form thermally-conductive interface with the sodium-wetted surfaces of the fuel assemblies. In the method, one or more spent fuel assemblies are removed from the sodium coolant pool and placed in a protective sheath. The remaining volume of the sheath is then filled with liquid Zamak. To a certain extent Zamak will dissolve and alloy with sodium remaining on the fuel assemblies. Excess sodium that remains undissolved is displaced from the sheath by the Zamak fill. The Zamak is then cooled until solid and the sheath sealed. The resulting Zamak-stabilized spent fuel assembly is calculated to have sufficient internal thermal conductivity to allow it to be stored and transported without the need for liquid cooling.
1. A method for preparing a spent nuclear fuel assembly for storage comprising:
providing a quantity of Zamak, the Zamak having a first melting point;
removing the spent nuclear fuel assembly from a liquid sodium environment while controlling the exposure of the spent nuclear fuel assembly to oxygen, thereby inhibiting formation of an oxide layer on the spent nuclear fuel assembly;
while controlling the exposure of the spent nuclear fuel assembly to oxygen, filling the spent nuclear fuel assembly with the liquid Zamak to obtain a Zamak-filled spent nuclear fuel assembly, thereby dissolving at least some liquid sodium in the spent nuclear fuel assembly into the Zamak and displacing any remaining liquid sodium from the spent nuclear fuel assembly;
cooling the Zamak-filled spent nuclear fuel assembly until the Zamak is at a temperature below the first melting point to obtain a Zamak-stabilized spent nuclear fuel assembly; and
dry storing the Zamak-stabilized spent nuclear fuel assembly.
2. The method of claim 1 , wherein the filling operation further comprises:
placing the spent nuclear fuel assembly in a sheath, the sheath made of a material having a second melting point greater than the first melting point; and
filling both the sheath and spent nuclear fuel assembly with liquid Zamak.
3. The method of claim 1 , wherein the Zamak is selected from Zamak 2, KS, Zamak 3, Zamak 4, Zamak 5, and Zamak 7.
4. The method of claim 3 , wherein the Zamak is Zamak 3.
5. The method of claim 2 , further comprising:
after filling the sheath with liquid Zamak, cooling the Zamak in the sheath to a temperature below the first melting point.
6. The method of claim 2 , further comprising:
placing the spent nuclear fuel assembly in the sheath under an inert environment; and
filling the sheath with liquid Zamak, thereby displacing the inert environment.
7. The method of claim 1 , further comprising:
draining liquid sodium from the spent nuclear fuel assembly.
8. The method of claim 2 , further comprising:
collecting sodium displaced from the sheath and the spent nuclear fuel assembly by the filling operations.
9. The method of claim 2 , further comprising:
after filling the sheath and the spent nuclear fuel assembly with Zamak, cooling the sheath.
10. The method of claim 9 , wherein the cooling operation further comprises:
cooling the sheath from the bottom.
11. The method of claim 2 , further comprising:
after filling the sheath and the spent nuclear fuel assembly with Zamak, placing the sheath in dry storage.
12. The method of claim 2 , further comprising:
after filling the sheath and the spent nuclear fuel assembly with Zamak, placing the sheath in a dry, subterranean storage location.
13. The method of claim 1 , wherein controlling the exposure of the spent nuclear fuel assembly to oxygen comprises:
maintaining the spent nuclear fuel assembly in a reduced-oxygen environment having less than 0.01 wt. % oxygen until it is filled with Zamak.
14. The method of claim 1 , wherein one or more operations of the method are performed without exposing the spent nuclear fuel assembly to oxygen.
15. The method of claim 1 , wherein one or more operations of the method are performed in an inert atmosphere.
16. The method of claim 1 , wherein the Zamak is an alloy having 1-10% Al;
0-1% Cu; 0.01-1% Mg; less than 0.5% of impurities (i.e., any element other than Al, Cu, Mg, and Zn); and the balance Zn.
17. The method of claim 2 , wherein the placing operation further comprises:
capping the sheath after placing the spent nuclear fuel assembly in the sheath.
18. The method of claim 2 , wherein the material having a second melting point greater than the first melting point is selected from 304 stainless steel, 316 stainless steel, and T91 steel.
19. A method for preparing a component with a surface exposed to sodium for storage comprising:
providing a quantity of Zamak, the Zamak having a first melting point;
displacing sodium from the surface with liquid Zamak to obtain a Zamak-coated surface on the component, thereby dissolving at least some sodium on the surface of the component into the Zamak and displacing any remaining sodium from the surface of the component; and
cooling the Zamak until the Zamak is at a temperature below the first melting point to obtain a Zamak-stabilized component.