Double-Walled Nuclear Waste Canister Closure for SCC Mitigation
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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 and compromise the integrity of the storage containers over time.
Innovation Solution
The development of a multi-thickness shell canister with a compact bolted closure lid and integrated reinforcement structures, along with advanced welding techniques such as hybrid laser welding and through-thickness compaction, minimizes residual tensile stresses and introduces compressive stresses to mitigate SCC, while also enhancing heat dissipation through radial cooling fins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hermetically seal welding is used to close the canister lid, then guaranteed confinement of radioactive material is achieved, but the stored fuel becomes difficult-to-access and requires cumbersome cutting operations for repackaging
Solution Approach 1:
The canister lid is segmented into a permanent seal portion (welded to the canister body) and a removable cover portion. The permanent seal provides guaranteed confinement integrity, while the removable cover allows easy access for repackaging operations without compromising the sealed joint.
Solution Approach 2:
The lid transitions from a static welded structure to a dynamic system where the cover portion can be removed and reattached. This allows the canister to switch between sealed storage mode and accessible repackaging mode, resolving the contradiction between permanent confinement and temporary access.
2Strength
If conventional welding is used on austenitic stainless steel canisters, then structural strength is achieved, but residual tensile stresses make the canister vulnerable to stress corrosion cracking in marine environments
Solution Approach 1:
The welding process incorporates preliminary anti-actions by using techniques that minimize residual tensile stresses and introduce compressive stresses during welding. This preemptive approach counteracts the development of SCC-vulnerable tensile stresses before they can compromise the canister in marine environments.
Solution Approach 2:
The welding parameters are changed to optimize the stress state in the weld zone. By controlling welding variables (such as heat input, welding sequence, and post-weld treatment), the process transforms the residual stress profile from tensile to compressive, thereby improving resistance to stress corrosion cracking while maintaining structural strength.
3Ease of manufacture
If a simple single-thickness shell is used, then manufacturing simplicity is maintained, but heat dissipation capability is insufficient for spent fuel storage
Solution Approach 1:
The canister shell employs local quality by using multi-thickness construction where different wall thicknesses are applied in specific regions. Thinner walls are used where heat dissipation is prioritized, while thicker sections provide structural strength where needed, optimizing both thermal performance and manufacturability.
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 the risk of SCC, maintaining structural integrity, and allowing for easier repackaging without the need for cumbersome cutting processes, while maintaining compatibility with existing storage systems.
Implementation Method 1
The canister includes a plurality of longitudinally-extending cooling fins protruding radially outwards from the shell
Implementation Method 2
The ventilation utilizes ambient cooling air to dissipate the considerable heat still emitted by the spent fuel
Implementation Method 3
The all-welded canister provides guaranteed confinement of the contents, but makes the stored fuel difficult-to-access if repackaging is required at a later date
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.