Nickel Alloy Steam Generator Tube Surface Treatment
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Solution Overview
Problem
Nuclear reactor steam generators face significant radioactive contamination due to the formation of nickel-rich filaments and the release of cobalt isotopes, which are activated from nickel in the reactor core, leading to high dose rates around the primary circuit.
Innovation Solution
A steam generator with a nickel-based alloy tube surface treated to maintain a significant mass content of available chromium throughout the superficial metallic layer, preventing the formation of nickel-rich filaments and reducing the release of radioactive isotopes by forming a chromium-rich oxide barrier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If nickel-based alloy tubes are used in steam generators, then the mechanical strength and corrosion resistance are improved, but radioactive contamination increases due to nickel activation forming cobalt isotopes
Solution Approach 1:
The patent applies a chromium-rich oxide layer specifically on the internal surface of the nickel-based alloy tubes where the primary liquid flows. This localized chromium enrichment creates a protective barrier precisely at the interface with the primary liquid, preventing nickel dissolution and activation without altering the bulk nickel-based alloy composition and its mechanical properties.
Solution Approach 2:
The patent creates a composite structure with a nickel-based alloy bulk material providing mechanical strength and a chromium-rich oxide surface layer providing radiation protection. This composite approach combines the advantages of nickel-based alloys (strength, corrosion resistance) with chromium oxide (low activation, protective barrier) to simultaneously achieve mechanical performance and reduced radioactive contamination.
2Use of energy by moving object
If the primary liquid circulates at high temperature to transfer heat efficiently, then the energy transfer is improved, but nickel dissolution and filament formation increase
Solution Approach 1:
The patent applies a chromium-rich oxide layer on the tube internal surface before the tubes are installed in the steam generator and before they are exposed to high-temperature primary liquid. This preliminary protective layer prevents nickel dissolution and filament formation during subsequent high-temperature operation, allowing efficient heat transfer without excessive nickel loss.
Solution Approach 2:
The chromium-rich oxide layer acts as an intermediary barrier between the nickel-based alloy tube material and the high-temperature primary liquid. This intermediate layer prevents direct interaction between the hot liquid and nickel metal, reducing nickel dissolution and activation while still allowing thermal energy to pass through for efficient heat transfer.
3Object-generated harmful factors
If the chromium content in the bulk alloy is increased to prevent nickel activation, then the radioactive contamination is reduced, but the manufacturing cost and alloy complexity increase
Solution Approach 1:
Instead of uniformly increasing chromium content throughout the bulk alloy, the patent concentrates chromium enrichment specifically in the oxide layer on the internal surface. This localized approach provides the radiation protection benefits of high chromium content while maintaining the cost-effective nickel-based alloy composition in the bulk material.
Solution Approach 2:
The patent extracts the radiation protection function from the bulk alloy composition and places it in a surface oxide layer. This separation allows the bulk alloy to remain a cost-effective nickel-based material while the surface layer provides the chromium-rich protection needed to prevent nickel activation and reduce radioactive contamination.
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 effectively limits the formation of nickel-rich filaments and reduces radioactive contamination in the primary circuit, thereby decreasing the release of cobalt isotopes and enhancing the safety and efficiency of nuclear reactor operations.
Implementation Method 1
a surface metallic layer having an internal surface covered with an oxide layer
Implementation Method 2
The primary liquid circulates inside the tubes and transfers its heat to the secondary liquid
Implementation Method 3
transfers its heat to the secondary liquid
Implementation Method 4
These isotopes are formed by activation of nickel in the reactor core, according to the following mechanism: Ni-58 + 1n → Co-58 + p
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The steam generator comprises at least one element (1) produced from a nickel alloy, the alloy having the following weight contents: - Ni greater than 50%; - Cr between 14% and 45%. According to the invention, the element (1) has a metal surface layer having, at a depth p from the inner surface, a weight content of chromium wCr(p), a weight content of carbon wc(p), and a weight content of available chromium wCr_dispo(p), where wCr_dispo(p)= wCr(p) − 16.61 wc(p). The weight content of available chromium wCr_dispo(p), taken as an average over the whole thickness of the metal surface layer from the inner surface, is greater than 0.