Simulation of Porous Magnetite Deposits on Steam Generator Tubes in Circulating Water at 270 °C

Abstract

In the secondary side of pressurized water reactors (PWRs), the main corrosion product accumulated on the steam generator (SG) tubes is magnetite, which has a porous structure. The purpose of this work is to simulate the porous magnetite deposited to the SG tubes using a loop system. We newly developed a circulating loop system for a porous magnetite deposition test. A test section was designed as a single hydraulic flow channel, and a cartridge heater was fabricated and mounted into a commercial SG tube to provide an equal heating source for the primary water. After the deposition test, the simulated magnetite deposits were characterized for comparison to real SG tube deposits collected from an operating PWR plant. The magnetite deposits produced using the loop system were appropriate for simulating the real SG tube deposits because the particle characteristics, phase, and porous morphology are closely similar to those of real deposit samples. Using the loop system, the chemical impurities such as Na and Cl can be easily concentrated within the pores of the simulated magnetite deposits. These simulated magnetite samples are expected to be widely utilized in various research fields such as the heat transfer degradation and magnetite accelerated corrosion of SG tubes.

Microstructural Characterization of the Corrosion Product Deposit in the Flow-Accelerated Region in High-Temperature Water

“…When the solution flows into flow cell I, the flow acceleration area forms in it, resulting in the rapid increase of streaming current, and then the transfer of wall current generated from the 304 SS to the metal/solution interface [15,16,22,30]. In the meantime, the "Karman vortex street" phenomenon will occur in the flow accelerated region, making the pressure difference between the micro-orifice on both sides increase, and causing a new current loop to promote particle deposition [19,[31][32][33][34]. According to previous calculations, the current was the highest at the edge of the flow accelerated region.…”

Effects of Advanced Amines on Magnetite Deposition of Steam Generator Tubes in Secondary System

“…Second, metallic impurities like Cu and Pb particles concentrate within the micropores, where they can electrically contact the surface of the SG tube and thus affect the galvanic acceleration of an SG tube because Cu and Pb particles act as cathodes of a galvanic couple [11]. In addition, Na, Cl, and S impurities concentrated within the micro-pores of SG tube deposits can cause various corrosion phenomena such as pitting corrosion and chloride-induced stress corrosion cracking [12,35,36]. One notable fact was that the deposit thickness was not constant.…”

“…First, SG tube fouling forms micro-crevices in which impurities could concentrate, potentially creating the aggressive corrosion environments that could lead to stress corrosion cracking (SCC), pitting corrosion, and eventually SG tube failure and/or plugging [9][10][11]. Second, SG tube fouling could also lead to less effective SG heat transfer efficiency [1,12]. Third, TSP clogging leads to the high velocity regions and transverse velocity in the secondary water flow, which causes flow-induced vibrations and SG tube cracks or failure [13].…”

Deposition of Colloidal Magnetite on Stainless Steel in Simulated Steam Generator Conditions—Experiments and Modeling

“…Despite considerable research efforts on the subject in recent years [5][6][7][8][9][10][11][12], currently, no generally applicable models of sludge deposition and consolidation processes have been proposed. The development of this type of model would include a quantitative assessment of the possibilities of minimizing the formation of magnetite particles and their deposition on the SG surfaces by optimizing the water chemistry and hydrodynamics (assessing the influence of different types of amines, the use of dispersants, etc.).…”