Abstract
Ethanolamine (ETA) is widely used to control the pH value in the secondary water of pressurized water reactors. However, it is necessary to consider other advanced amines which can replace ETA due to its serious human hazards and environmental treatment problems. The purpose of this study is to contemplate the effects of three advanced amines (ETA, 3-methoxypropylamine (MPA), and dimethylamine (DMA)) on the magnetite deposition behavior of a thermally treated (TT) Alloy 690 tubes by using a steam generator (SG) tube fouling loop in simulated secondary water. All particles were identified as a magnetite and were polyhedral or spherical in shape. When using ETA, MPA, and DMA, the average porosity of the deposits was about 34.7%, 33.0%, and 24.6%, respectively. The amount of deposits was largest when ETA was added, and it decreased by 41% when adding MPA and 55% when adding DMA. The mechanism of magnetite deposition was discussed in terms of zeta potentials of both the magnetite particles and the Alloy 690TT surface and magnetite solubility depending on the amines. To compare the potential for replacing ETA with other advanced amines, the various factors such as SG integrity, human hazards, and environmental treatment problems were discussed.
Highlights
The secondary water systems of pressurized water reactors (PWR) inevitably generate the corrosion products that are transported into the steam generator (SG) through the feedwater [1,2]
Most of the corrosion products in SG typically originate from flow accelerated corrosion (FAC) of carbon steel tubing and other carbon steel components
In spite of blowdown system operation for the removal of impurities, the magnetite remaining in the final feedwater accumulates on surfaces within the SG shell [6,7]
Summary
The secondary water systems of pressurized water reactors (PWR) inevitably generate the corrosion products that are transported into the SG through the feedwater [1,2]. The resulting deposits occur in the form of magnetite [3,4,5]. The magnetite deposits in SGs may result in clogging at the top of the tube support plate (TSP) and in SG tube fouling [1,2]. 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]. 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]
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