Zamak Stabilization of Spent Sodium-Cooled Reactor Fuel
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Solution Overview
Problem
Spent nuclear fuel assemblies from sodium-cooled reactors face overheating due to decay heat, and existing void-filling methods fail due to gap formation between the filling material and the fuel assembly components, which reduces heat transfer efficiency.
Innovation Solution
The method involves using Zamak, a thermally conductive alloy, to fill the fuel assembly, where Zamak dissolves and alloys with sodium, preventing oxide layer formation and ensuring a good metallic bond, thus maintaining heat transfer efficiency without the need for liquid cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a thermally-conductive metal or metal alloy is used to fill the spent fuel assembly, then the thermal conductivity is improved and heat transfer is enhanced, but gap formation occurs between the void-filling material and fuel assembly components which reduces heat transfer efficiency
Solution Approach 1:
The invention changes the chemical composition parameters of the void-filling material by incorporating reactive elements (such as aluminum, magnesium, or zinc) that can chemically react with sodium oxide layers on fuel assembly components. This parameter change transforms the material properties to enable chemical bonding rather than physical contact only, eliminating gaps and ensuring reliable heat transfer while maintaining high thermal conductivity.
2Duration of action of stationary object
If conventional void-filling materials are used, then the fuel assembly can be stabilized for dry storage, but oxide layers on fuel assembly surfaces prevent good metallic bonding and cause gap formation
Solution Approach 1:
The invention introduces reactive elements (aluminum, magnesium, or zinc) as intermediaries between the void-filling material and the sodium oxide layer on fuel assembly components. These intermediaries chemically react with the oxide layer to form strong metallurgical bonds, acting as a bridge that connects the void-filling material to the fuel assembly components and eliminates gaps that would otherwise form due to oxide layer interference.
Solution Approach 2:
The invention creates a chemically reactive environment within the void-filling material that can actively interact with and remove oxide layers, essentially transforming the inert oxide barrier into a reactive interface that promotes bonding. The reactive elements in the void-filling material serve to chemically reduce or react with the sodium oxide layer, converting it from a bonding barrier into a bonding facilitator.
3Temperature
If wet storage is used to remove decay heat, then overheating is prevented, but long term storage requires maintaining pool integrity which increases cost and complexity
Solution Approach 1:
The invention enables the spent fuel assembly to serve its own cooling function through the high thermal conductivity of the void-filling material. The thermally-conductive material fills all void spaces within the fuel assembly, creating internal thermal pathways that conduct decay heat from the fuel rods to the external surfaces where it can be dissipated to the environment, eliminating the need for external water pools or active cooling systems.
Solution Approach 2:
The invention extracts the cooling function from the external water storage system and transfers it to the internal structure of the fuel assembly itself. By incorporating thermally-conductive void-filling material within the fuel assembly, the cooling capability is built into the fuel structure, removing the dependency on external wet storage infrastructure and enabling simplified dry storage.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively stabilizes spent fuel assemblies by preventing oxide layer-induced gap formation, ensuring sufficient internal thermal conductivity for safe storage and transportation without liquid cooling.
Implementation Method 1
To a certain extent Zamak will dissolve and alloy with sodium remaining on the fuel assemblies
Implementation Method 2
The Zamak is then cooled until solid
Implementation Method 3
the thermal conductivity of the stabilized spent fuel assembly could be sufficient to prevent the components from getting unacceptably hot by quickly transporting the decay heat to the exterior of the fuel assembly
Data Source
AI summary
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.