Neutron Shield Void Design for Cask Thermal Stress
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Solution Overview
Problem
The existing cask designs face significant stress due to the thermal expansion of neutron shielding materials, which have higher thermal expansion coefficients than the cask body and outer cylinder materials, potentially leading to structural issues during the storage and transport of spent fuel assemblies.
Innovation Solution
The cask design incorporates neutron shields with a molded pipe portion and a filled portion, where the molded pipe portion is formed of a neutron shielding material with a hollow void extending axially, and the filled portion is formed by filling the space between the molded pipe portion and the outer edge of the divided space with the same neutron shielding material, allowing for thermal expansion absorption and reduced stress on the outer cylinder and other components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If neutron shielding material is used to fill the space between cask body and outer cylinder, then neutron radiation attenuation is improved, but thermal expansion stress on outer cylinder increases
Solution Approach 1:
The neutron shielding is divided into multiple independent neutron shields, each containing void portions that act as expansion buffers. This segmentation allows the shielding material to expand locally without transmitting stress to the outer cylinder, resolving the contradiction between maintaining shielding integrity and reducing thermal stress.
Solution Approach 2:
Void portions are intentionally created within the neutron shielding material structure. These voids serve as expansion spaces that accommodate thermal expansion of the neutron shielding material when fuel assemblies are housed in the cask, thereby reducing stress on the outer cylinder while maintaining neutron attenuation performance.
2Object-affected harmful factors
If neutron shielding material with high thermal expansion coefficient is used, then neutron radiation shielding effectiveness is improved, but structural integrity of cask is compromised
Solution Approach 1:
Void portions are pre-configured within the neutron shielding structure before the fuel assembly is placed in the cask. These voids act as predetermined cushioning spaces that will accommodate thermal expansion when the neutron shielding material heats up, preventing structural damage to the cask while maintaining shielding effectiveness.
Solution Approach 2:
The neutron shielding incorporates void portions creating a porous-like structure that allows for volume expansion of the shielding material during thermal cycles. This maintains the structural integrity of the entire cask system by providing internal accommodation space for expansion without compromising the outer cylinder or cask body.
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 design effectively reduces the stress exerted on the outer cylinder and other components by absorbing thermal expansion, maintaining structural integrity and preventing the generation of unexpected shieldless portions during temperature changes.
Implementation Method 1
the neutron shielding material has a higher thermal expansion coefficient than materials (e.g., carbon steel) used for the cask body and the outer cylinder, and therefore great stress may be exerted on the outer cylinder or other components by thermal expansion of the neutron shielding material
Data Source
AI summary
A cask includes a cask body, an outer cylinder, a plurality of fins, and a plurality of neutron shields. The cask body has a tubular shape around a central axis and is capable of housing fuel assemblies. The outer cylinder has a tubular shape surrounding the cask body. The fins are aligned in a circumferential direction in a tubular space formed between the cask body and the outer cylinder, and connect an outer peripheral surface of the cask body and an inner peripheral surface of the outer cylinder to divide the tubular space into a plurality of divided spaces. The neutron shields contain a neutron shielding material with which the divided spaces are filled. Each neutron shield includes a void portion extending in the axial direction along the central axis. Accordingly, it is possible to reduce stress that may be exerted on the outer cylinder or other components by thermal expansion of the neutron shielding material when the fuel assemblies are housed in the cask.