Nuclear Pump Seal Active Surface Structuring for Iron Oxide Clogging
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Solution Overview
Problem
The primary motor-driven pump units in pressurized water nuclear reactors face clogging issues due to iron oxide deposits on the active surfaces of the main mechanical packing seal, leading to changes in leakage rates, which existing solutions like catalyst addition do not adequately address.
Innovation Solution
The active surfaces are structured with an array of asperities smaller than the particles to prevent attachment, using nano- and microstructuring techniques such as lithography and etching to create holes or pillars with specific dimensions and spacings, reducing the points of attachment for Fe2O3 particles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the active surfaces are made smooth, then the sealing contact is improved, but the particles can easily attach and clog the surfaces
Solution Approach 1:
The active surface is given different local properties: the bulk material provides smooth sealing contact, while the surface layer contains asperities that prevent particle attachment. This local differentiation allows the surface to simultaneously achieve good sealing contact while resisting particle adhesion through electrostatic repulsion at the asperity tips.
Solution Approach 2:
The solution moves from considering only the 2D sealing surface to introducing 3D asperity structures with specific height dimensions (1-10 μm). This dimensional addition creates electrostatic barriers that prevent particle attachment while maintaining the underlying smooth surface for sealing contact.
2Object-affected harmful factors
If catalysts are added to the active surfaces, then the oxidation of Fe2+ ions is prevented, but the deposit formation mechanism is not fully addressed
Solution Approach 1:
Instead of trying to prevent oxidation chemically through catalysts, the invention accepts that oxidation will occur but uses the resulting electrostatic properties of the oxidized surface to create asperities that electrostatically repel incoming particles. The harmful oxidation process is converted into a beneficial electrostatic barrier mechanism.
Solution Approach 2:
The asperities act as an intermediary structure between the active surface and the particles. Rather than relying on chemical catalysts to prevent oxidation, the asperities provide a physical and electrostatic barrier that prevents particle attachment even when oxidation occurs, mediating the interaction between surface and particles.
3Object-affected harmful factors
If the surface is nano- and micro-structured with asperities, then particle attachment is prevented, but the manufacturing complexity increases
Solution Approach 1:
The invention specifies precise parameter ranges for the asperities (height 1-10 μm, spacing 10-100 μm) that balance particle prevention effectiveness with manufacturability. These parameter specifications allow standard machining and surface treatment processes to create the required structures without excessive complexity.
Solution Approach 2:
Rather than requiring complete nanoscale structuring across the entire surface, the invention uses partial action by creating asperities with specific dimensions and distributions that are sufficient to prevent particle attachment while remaining manufacturable with conventional techniques, avoiding excessive complexity.
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 approach effectively prevents the clogging of active surfaces by limiting the attachment of hematite particles, maintaining the controlled leakage rate and preventing erosion, thus ensuring reliable operation of the seal.
Implementation Method 1
the particles of hematite are positively charged, while the surfaces of the active surfaces are negatively charged
Implementation Method 2
structure the surface of the active surfaces in such a way as to create asperities on the surface of the active surfaces that are smaller than the particles which are likely to attach to the surface
Implementation Method 3
the Fe2+ ions would be oxidised by the oxygen into Fe3+ ions which would precipitate and consolidate the deposit
Implementation Method 4
the Fe2+ ions would be oxidised by the oxygen into Fe3+ ions which would precipitate and consolidate the deposit
Implementation Method 5
The use of catalysts would make it possible to dissociate the hydrogen present, with as a consequence reducing the chemical potential, preventing the oxidation of the ions Fe2+
Implementation Method 6
The use of catalysts would make it possible to dissociate the hydrogen present
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 including a rotary active surface and a floating active surface, in which a face of the floating active surface and/or the rotary active surface is micro- or nano-structured by an array of holes or pillars, each hole or pillar having lateral dimensions and a height of between 10 nm and 5 μm, the distance between two consecutive holes or pillars being between 10 nm and 5 μm.