Protective Coating for Nuclear Pump Shaft Seals
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Solution Overview
Problem
The primary motor-driven pump units of pressurized water nuclear reactors face significant fouling of active surfaces due to iron oxide deposition, which alters the leakage rate and is caused by the interaction of hematite particles with the active surfaces, primarily driven by the adsorption of Fe2+ ions.
Innovation Solution
A protective layer with a surface energy greater than 30 mJ/m2 and an electron donor component less than 15 mJ/m2 is applied to the active surfaces to prevent Fe2+ ions from adsorbing, using materials like nano- or micro-crystalline diamond, titanium nitride, chromium nitride, chemical nickel, or silicon carbide, and optionally structured with micro- or nano-features to further inhibit fouling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the active surfaces are made of silicon nitride to improve abrasion resistance, then the durability is improved, but the electron donor component increases leading to faster iron oxide deposition
Solution Approach 1:
A protective layer is introduced as an intermediary between the silicon nitride active surface and the Fe2+ ions in the coolant. This protective layer has low electron donor component and high surface energy, preventing Fe2+ adsorption while allowing the silicon nitride to maintain its abrasion resistance properties.
Solution Approach 2:
The solution uses a composite structure combining the silicon nitride base material with a protective coating layer. The composite maintains the beneficial abrasion resistance of silicon nitride while adding the protective properties of low electron donor component materials, effectively addressing both requirements.
2Ease of operation
If the surface energy is increased to improve wetting properties, then the fluid contact is improved, but the electron donor component may increase leading to more Fe2+ adsorption
Solution Approach 1:
The protective layer is designed with specific parameter ranges: surface energy greater than 30 mJ/m2 for good wetting, but electron donor component less than 15 mJ/m2 to prevent Fe2+ adsorption. This precise parameter control resolves the contradiction between wetting properties and fouling resistance.
3Object-affected harmful factors
If a protective layer is added to prevent Fe2+ adsorption, then the fouling resistance is improved, but the device complexity increases
Solution Approach 1:
By specifying precise material parameters (surface energy >30 mJ/m2, electron donor component <15 mJ/m2), the invention provides clear selection criteria for protective materials, simplifying the design and selection process despite adding a layer.
Solution Approach 2:
The protective layer is applied specifically to the active surfaces where fouling occurs, rather than treating the entire sealing system. This localized approach minimizes the added complexity while maximizing the protective benefit at the critical interface.
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 protective layer effectively delays and reduces iron oxide deposition on the active surfaces, maintaining the integrity of the sealing system by preventing Fe2+ ions from adsorbing and reacting with hematite particles, thereby stabilizing the leakage rate and extending the time before significant fouling occurs.
Implementation Method 1
the deposition is only performed in the fields of the Pourbaix diagram where Fe2+ is the thermodynamically stable species... it was demonstrated that the deposition occurred on a low energy face, which is a poor electron donor
Implementation Method 2
deposition also occurs on a high energy surface which is a strong electron donor component such as silicon nitride... deposition is strongly delayed on a high energy microcrystalline diamond face with a low electron donor component
Data Source
AI summary
A packing seal is provided for a system for sealing the shaft of a primary motor-driven pump unit of a nuclear reactor, intended to ensure sealing between the primary circuit and the atmosphere. The packing seal includes a rotary active surface and a floating active surface, and a face of the floating active surface and/or the rotary active surface is covered by a protective layer made from a material having surface energy greater than 30 mJ/m.sup.2 and an electron donor component less than 15 mJ/m.sup.2.