Low-Temperature Zinc Deposition for Nuclear Coolant Loop Radiation Reduction
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Solution Overview
Problem
Nuclear power plants face challenges in reducing radiation fields and corrosion in coolant loop piping due to activated corrosion products, which are incorporated into oxide films during high-temperature operation, leading to increased worker exposure and corrosion issues like PWSCC and IGSCC.
Innovation Solution
A method for low-temperature zinc deposition during refueling outages or before hot functional testing, where a treatment solution containing zinc and optional noble metals is applied to the coolant loop surfaces, forming an adherent layer that is incorporated into oxide films during subsequent high-temperature operation, reducing the incorporation of activated corrosion products and enhancing corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If zinc is injected into the primary coolant loop during normal high-temperature operation, then radiation fields are reduced by competing with activated corrosion products for incorporation into oxide films, but zinc may be preferentially deposited on fuel assemblies increasing operability and corrosion risks
Solution Approach 1:
Zinc is deposited onto coolant loop surfaces at low temperature before the plant begins power-generating operation or during refueling outages. This preliminary deposition ensures zinc is present on piping surfaces before high-temperature operation begins, allowing zinc to be incorporated into oxide films during subsequent operation without requiring zinc injection during power operation, thereby avoiding preferential deposition on fuel assemblies
Solution Approach 2:
The patent changes the temperature parameter from high-temperature injection (during power operation) to low-temperature deposition (below 260°C, during outages or before operation). This parameter change fundamentally alters the deposition behavior, enabling zinc to deposit on piping surfaces without preferential accumulation on fuel assemblies while still achieving the desired radiation field reduction
2Object-affected harmful factors
If zinc is deposited during refueling outages at low temperature, then zinc can be incorporated into oxide films during subsequent operation reducing activated corrosion products, but oxide formation is generally negligible under refueling outage conditions
Solution Approach 1:
Zinc deposition is performed as a preliminary action during refueling outages at low temperature, preparing the piping surfaces with zinc before power operation begins. Although oxide formation is negligible during outages, the deposited zinc remains on surfaces and is incorporated into oxide films during subsequent high-temperature operation, achieving the desired effect of reducing activated corrosion product incorporation
Solution Approach 2:
The process is segmented into two distinct phases: (1) low-temperature zinc deposition during refueling outages when oxide formation is negligible, and (2) high-temperature operation where oxide films form and incorporate the previously deposited zinc. This segmentation allows each phase to occur under optimal conditions
3Object-affected harmful factors
If chemical decontamination is performed to remove previously formed oxide films containing radioactive species, then radiation fields are reduced, but the surfaces become devoid of protective oxide layers
Solution Approach 1:
Zinc deposition is performed as a preliminary action after chemical decontamination removes radioactive oxide films. The zinc deposits on the freshly cleaned surfaces, and when the plant returns to operation, new oxide films form incorporating this zinc, providing both radiation field reduction and corrosion protection
Solution Approach 2:
The chemical decontamination process, which removes protective oxide layers, is converted into a benefit by creating clean surfaces that readily accept zinc deposition. The subsequently formed oxide films incorporate this zinc, providing enhanced protection against both radiation and corrosion
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 reduces radiation fields, lowers worker exposure, and mitigates corrosion in nuclear power plant piping by forming oxide films enriched with zinc and noble metals, thereby reducing PWSCC and IGSCC, while minimizing the risk of zinc deposition on fuel assemblies.
Implementation Method 1
deposition of zinc particles on coolant loop piping materials such as stainless steel can be achieved at low temperature
Implementation Method 2
these particles remain adherent to the piping materials of construction when the plant returns to operating conditions and temperatures. As a result, the oxide films that subsequently form on these surfaces during normal power-generating operation are enriched in zinc
Implementation Method 3
zinc competes with activated corrosion products (Co-58, Co-60, etc.) typically observed in reactor water in nuclear power plants for incorporation into oxide films
Data Source
AI summary
A method for depositing zinc on the surfaces of a coolant loop of a nuclear power plant includes: providing within a portion of the coolant loop a treatment solution comprising zinc and optionally one or more noble metals and/or reducing agent(s); allowing the treatment solution to remain in the portion for a treatment period; and removing the treatment solution from the portion. According to various embodiments, an average temperature of the treatment solution over the course of the treatment period is less than 150° C. or 100° C. According to various embodiments, an instantaneous temperature of the treatment solution remains below 150° C. or 100° C. throughout the treatment period. The zinc deposition treatment may be applied (1) before the plant is first put into power-generating operation or (2) during an outage following power-generating operation and optionally following a chemical decontamination to remove any oxides formed on surfaces of a coolant loop during prior power operation period(s).