Concrete Cask Baffle Plate Suppresses Stress Corrosion Cracking
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Solution Overview
Problem
Conventional concrete casks for storing spent nuclear fuel are prone to stress corrosion cracking (SCC) due to salt-laden air introducing chloride ions at the lid welded part, which is difficult to manufacture without residual tensile stress in high-concentration radioactivity environments.
Innovation Solution
A concrete cask design incorporating a baffle plate to suppress air rising through the cooling passage from reaching the top space, with a mounting bracket having a lower thermal expansion coefficient than the canister material to securely fasten the baffle plate and prevent salt-laden air from contacting the lid welded part, and optionally using a cover plate to further protect the lid welded part.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the lid welded part is manufactured in high-concentration radioactivity atmosphere, then the canister can be sealed after fuel loading, but residual tensile stress remains causing stress corrosion cracking
Solution Approach 1:
The canister is divided into two manufacturing stages: the canister body is manufactured and prepared in advance in a low-radioactivity environment where weld quality can be controlled, then the lid is attached in the high-radioactivity environment after fuel loading. This segmentation allows critical welding operations to be performed when corrosion risk is minimal.
Solution Approach 2:
The canister body is prepared in advance with pre-welded sections and structural components before fuel loading. This preliminary action in a controlled environment ensures high-quality welds without residual stress, while the final lid attachment occurs in the radioactive environment where stress corrosion is less of a concern.
2Temperature
If cooling air flows freely through the cooling passage to the top space, then heat dissipation is efficient, but salt-laden air contacts the lid welded part causing chloride ion generation
Solution Approach 1:
The interior surface of the lid is provided with a heat radiating member that selectively enhances heat radiation in the region away from the welded part. This local quality enhancement allows efficient heat dissipation while protecting the vulnerable welded area from salt-laden air contact.
Solution Approach 2:
A protective coating or barrier layer is applied to the interior surface of the lid in the region corresponding to the welded part. This intermediary layer prevents direct contact between salt-laden air and the welded metal, while still allowing heat transfer through radiation.
3Strength
If a thick metal cylinder is used for the cask, then radiation shielding and structural strength are sufficient, but manufacturing cost increases significantly
Solution Approach 1:
The cask structure uses a composite design combining a thin-walled metal canister for fuel containment with a concrete container body for radiation shielding and structural support. This composite approach leverages the strengths of both materials: metal provides corrosion resistance and tight sealing, while concrete provides cost-effective radiation shielding and mechanical strength.
Solution Approach 2:
The radiation shielding function is extracted from the metal cylinder and assigned to a separate concrete container body. This allows the metal canister to be optimized for its primary function of fuel containment with minimal wall thickness, while the concrete structure provides the necessary shielding and structural support at lower cost.
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
Effectively suppresses the generation of chloride ions and occurrence of stress corrosion cracking on the canister's lid welded part, enhancing the reliability of the concrete cask by preventing direct contact between salt-laden air and the lid welded part.
Implementation Method 1
a mounting bracket having a lower thermal expansion coefficient than the canister material to securely fasten the baffle plate
Implementation Method 2
cooling air is introduced in the bottom end part of the cooling passage through the air introduction passages 104, and thereafter is naturally circulated upward while being warmed by decay heat emitted from the canister 102
Data Source
AI summary
A concrete cask enabling suppression of occurrence of stress corrosion cracking (SCC) in a lid welded part of a canister. The concrete cask includes: a metal canister accommodating spent fuel; a concrete container body for accommodating the canister inside the container body; a cooling passage provided between the external peripheral surface of the canister and the internal peripheral surface of the container body, and allowing air for cooling the external peripheral surface of the canister to pass; and a top space provided between the top surface part of the canister, and the inside of a lid of the container body. A baffle plate for suppressing introduction of air rising through the cooling passage to the top space is provided.