SiC/SiC Composite Control Rod for Weight and Corrosion Management
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Solution Overview
Problem
The existing reactor control rods face challenges with increased weight due to higher neutron absorption materials like Hf, leading to weight restrictions, corrosion issues, and potential hydrogen generation from metal-water reactions, which can damage the containment vessel and cause unintended criticality during high-temperature events.
Innovation Solution
A reactor control rod design utilizing SiC-fiber-reinforced SiC composite material for the central joint and wing sections, providing a lightweight, corrosion-resistant, and heat-resistant structure that maintains reactivity control even at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amount of Hf is increased to achieve higher control rod worth, then the neutron absorption capability is improved, but the weight of the control rod increases due to the high density of Hf (13.3 g/cm³)
Solution Approach 1:
The patent applies composite materials by combining Hf neutron absorbing members with a Zr-based alloy sheath. This composite structure allows the control rod to achieve high neutron absorption capability through Hf while the Zr-based alloy provides low density (reducing weight) and high melting point (improving heat resistance). The composite material approach resolves the contradiction between needing high Hf content for control rod worth and maintaining acceptable weight.
2Strength
If stainless steel sheaths are used to store Hf, then the structural integrity is maintained, but corrosion advances between different metals and sliding friction increases due to corrosion products
Solution Approach 1:
The patent changes the material parameter of the sheath from conventional stainless steel to a Zr-based alloy. This parameter change fundamentally alters the corrosion behavior by eliminating galvanic corrosion between dissimilar metals (stainless steel and Hf), as Zr-based alloys have compatible electrochemical properties with Hf. The Zr-based alloy sheath maintains structural integrity while providing superior corrosion resistance and reducing sliding friction.
3Strength
If metallic materials like stainless steel are used for control rods, then the structural strength is adequate, but hydrogen gas is generated through metal-water reaction at high temperatures
Solution Approach 1:
The patent changes the material composition parameter by using a Zr-based alloy instead of conventional stainless steel. This parameter change eliminates the harmful effect of hydrogen generation through metal-water reaction, as Zr-based alloys have significantly lower hydrogen generation rates compared to stainless steel at high temperatures. The Zr-based alloy maintains adequate structural strength while preventing hydrogen production that could compromise containment vessel integrity.
4Ease of manufacture
If conventional stainless steel is used for control rods, then the manufacturing process is established, but the melting point is limited at about 1,400 degrees Celsius
Solution Approach 1:
The patent changes the material parameter from stainless steel to Zr-based alloy, which fundamentally alters the melting point parameter from approximately 1,400°C to above 1,850°C. This parameter change provides a safety margin ensuring the control rod maintains structural integrity even if the reactor core temperature exceeds normal operating ranges. The Zr-based alloy offers superior high-temperature performance while being manufacturable using established metallurgical processes.
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 SiC/SiC composite control rod reduces weight, prevents hydrogen generation, and enhances structural integrity, allowing for effective reactivity control and preventing damage to the containment vessel during high-temperature events.
Implementation Method 1
at least part of the central joint section and the wing surface structural member is made of SiC-fiber-reinforced SiC composite material
Implementation Method 2
The melting point of stainless steel, which is a structural material of the conventional control rods, is about 1,400 degrees Celsius. Meanwhile, fuel cladding tubes and the channel boxes are made of the Zr alloy; the melting point of Zr is about 1,850 degrees Celsius.
Implementation Method 3
When a critical event, such as loss of power, occurs due to a large-scale natural disaster, the insertion of control rods can shut a nuclear reactor. However, if the core cooling system fails to actuate, decay heat of fission products in the fuel or like may cause temperature rise of the nuclear reactor. In the reactor internal structure of BWR, metallic materials have been mainly used, such as a Zr alloy for fuel rods and channel boxes and stainless steel for control rods. These metallic materials are oxidized by high-temperature steam through a metal-water reaction, to generate hydrogen gas.
Implementation Method 4
Some control rods use Hf stored in stainless steel sheaths. Then, corrosion advances between different metals, or between stainless steel and Hf, and the sliding friction between Hf and the stainless-steel sheath becomes higher due to corrosion products.
Data Source
AI summary
A nuclear reactor control rod with SiC fiber reinforced structure comprises wing sections and a central joint section. Each of the wing sections is a flat plate spreading axially and radially, and includes storage tubes and a wing surface structural member. The storage tubes are arranged in parallel in a flat plane and contain a neutron absorbing member containing the neutron absorbing material. The wing surface structural member is formed by molding of SiC/SiC composite material as to cover surfaces of the storage tubes and formed to have an outward shape of a flat plate. The central joint section and storage tubes are made of SiC/SiC composite material. The central joint section bundles the wing sections together at center. The storage tubes are bundled together with fibers made of SiC or a textile made of SiC.