Double-Walled Nuclear Waste Canister Welding to Prevent SCC
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Solution Overview
Problem
Traditional spent nuclear fuel canisters made of austenitic stainless steel are vulnerable to stress corrosion cracking (SCC) due to residual tensile stresses and exposure to salt-laden marine environments, which can lead to degradation over time, necessitating improved storage solutions that prevent SCC.
Innovation Solution
The development of a multi-thickness shell canister with a compact bolted closure lid and enhanced heat dissipation features, incorporating a radially thickened mounting boss and radial cooling fins, along with welding processes that minimize residual tensile stresses and induce compressive stresses through techniques like hybrid laser welding and through-thickness compaction, to prevent SCC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional austenitic stainless steel canisters are used for spent fuel storage, then the canisters provide basic containment and shielding, but they are vulnerable to stress corrosion cracking (SCC) in salt-laden marine environments due to residual tensile stresses
Solution Approach 1:
The patent applies parameter changes by transitioning from conventional welding processes to hybrid laser welding, which fundamentally alters the thermal and mechanical parameters of the welding process. This results in minimized residual tensile stresses and induced compressive stresses in the weld zone, directly resolving the SCC vulnerability issue while maintaining the canister's containment function
Solution Approach 2:
The patent replaces traditional mechanical welding processes with hybrid laser welding technology. This substitution introduces a more advanced welding system that combines laser heating with filler metal deposition, enabling precise control over stress distribution and eliminating the residual tensile stresses that cause SCC in conventional welded canisters
2Reliability
If seal welded lids are used on canisters, then guaranteed confinement of radioactive contents is achieved, but the stored fuel becomes difficult-to-access if repackaging is required
Solution Approach 1:
The patent applies dynamics by transforming the static, permanent weld connection into a dynamic, controllable connection. The bolted lid with high-intensity fasteners provides a reversible mechanical connection that maintains confinement during storage but allows controlled access when repackaging is needed, resolving the contradiction between security and accessibility
Solution Approach 2:
The patent segments the lid from the canister body by replacing the monolithic welded connection with a bolted flanged joint. This segmentation allows the lid to be independently removed and reattached, providing both guaranteed confinement when closed and easy accessibility when opened, without compromising the integrity of the containment system
3Strength
If conventional welding processes are used to join canister components, then structural integrity is achieved, but residual tensile stresses are created that promote stress corrosion cracking
Solution Approach 1:
The patent fundamentally changes the welding parameters by adopting hybrid laser welding instead of conventional arc welding. This parameter change results in a completely different stress profile in the weld zone, producing compressive residual stresses instead of tensile stresses, while maintaining full structural integrity of the canister components
Solution Approach 2:
The patent substitutes conventional welding mechanics with hybrid laser welding mechanics. The laser beam provides precise localized heating followed by controlled filler metal deposition, creating a welding process that inherently produces compressive stresses through rapid cooling and phase transformation, eliminating the need for post-weld stress relief operations
4Duration of action of stationary object
If spent fuel is stored in dry inert gas atmosphere, then long-term storage is enabled, but effective heat dissipation becomes challenging
Solution Approach 1:
The patent applies local quality by providing enhanced cooling specifically at the fuel assembly locations within the canister. The design includes localized cooling channels and thermal management features positioned to maximize heat removal from the high-heat-generating fuel regions while maintaining the overall dry inert gas atmosphere for long-term storage stability
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
The solution provides a more accessible and safer storage system for spent nuclear fuel, reducing radiation exposure and extending the service life of canisters by preventing SCC, while maintaining compatibility with existing storage infrastructure and ensuring effective heat management.
Implementation Method 1
hybrid laser welding
Implementation Method 2
induce compressive stresses through techniques like hybrid laser welding
Implementation Method 3
through-thickness compaction, to prevent SCC
Implementation Method 4
radial cooling fins
Implementation Method 5
enhanced heat dissipation features
Implementation Method 6
compact bolted closure lid
Data Source
AI summary
A dry storage systems for radioactive nuclear waste materials may include a double-walled canister system. The canister system may include a canister having a tubular inner shell defining an internal cavity for storing nuclear waste material, a first lid sealably welded to a first end of the inner shell, a primary base plate defining a peripheral edge portion and having an annular closure flange, and an annular full thickness butt weld formed at an abutment joint between the annular closure flange and a second end of the inner shell. The inner shell, first lid, and first end closure may collectively define a sealed primary pressure retention barrier. A tubular outer shell may adjoin the inner shell. The outer shell may be welded to the canister to form a hermetically sealed secondary pressure retention barrier.