Abstract
CRUD (Chalk River Unidentified Deposit) forms in the water circuits of nuclear reactors due to corrosion of structural materials and the consequent release of species into the coolant. The deposition of CRUD is known to occur preferentially in regions of the primary circuit of pressurised water reactors (PWRs) where the water flow accelerates. In order to investigate this phenomenon, a micro-fluidic system, recreating plant conditions while using a simplified experimental set-up, was realised. A flow cell, comprising a stainless steel disc with a central micro-orifice, was used to create accelerated flow under representative operating conditions. By monitoring the pressure drop across the cell, the build-up rate (BUR) of CRUD within the micro-orifice was monitored in real time. By this setup, the conditions inducing deposition of CRUD under PWR conditions were emulated and CRUD deposition was induced in the accelerated flow region. Further effects associated with the presence of lithium hydroxide were investigated in real-time.
Highlights
CRUD (Chalk River unidentified deposit) is a term that is used to describe corrosion products that are found in the water circuits of nuclear reactors due to the corrosion of structural materials, and were first observed at the Chalk River power plant.[1]
The magnitude of streaming currents that can be generated depends on a number of factors including solution water chemistry,[8] flow velocity,[17] electrochemical potential[18] and material.[19]
The CRUD that formed during the experiments was characterised using Raman spectroscopy (Renishaw RM System 1000 Mk1 with Renishaw RL633 Helium Neon 633 nm 20 mW laser) and Scanning electron microscopy (SEM) (FEI Magellan FEG-SEM)
Summary
CRUD (Chalk River unidentified deposit) is a term that is used to describe corrosion products that are found in the water circuits of nuclear reactors due to the corrosion of structural materials, and were first observed at the Chalk River power plant.[1]. Electrokinetic effects might arise when a metal comes into contact with a solution; a surface charge forms on the metal, and ions in solution rearrange to maintain charge neutrality within the local region. This generates an ‘electric double layer’ with a static layer immediately adjacent to the metal, and a diffuse layer where ions can be sheared from the metal by hydrodynamic flow.[15] The shearing of ions generates a streaming current parallel to the metal surface. The magnitude of streaming currents that can be generated depends on a number of factors including solution water chemistry,[8] flow velocity,[17] electrochemical potential[18] and material.[19]
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