Papers by Author: Uh Chul Kim

Abstract: In the nuclear power plants (NPPs), wall thinning of the piping materials is generally caused by a flow-accelerated corrosion (FAC) and leads to a rupture with no warning unless it is detected and repaired in a timely manner. To reduce the FAC, it is better to use low-alloy steels, such as 1Cr-½Mo and 2¼Cr-1Mo, having higher FAC-resistance than carbon steel. Meanwhile, in the secondary water chemistry at the NPPs in Korea, hydrazine concentration is maintained within the range of 100~150 ppb. For applying these low-alloys to a piping material, we investigated the influence of hydrazine concentration on their FAC. An experiment was carried out at pH25°C of 9 controlled with ammonia in a deoxygenated aqueous solution containing 0~250 ppb-hydrazine by using a FAC test loop at 250°C for 300 hours. Experimental weight loss showed a hydrazine concentration dependency of the FAC in this concentration range, giving minimum at 150 ppb.

Abstract: Several chemicals were studied to suppress the damage due to stress corrosion cracking (SCC) of steam generator (SG) tubes in nuclear power plants. The polarization curves showed that the electrochemical properties on the surface of Alloy 600 MA changed with the addition of inhibitors. The SCC tests were conducted by using a m-RUB specimen in a 10% NaOH solution at a temperature of 315°C. The effects on the SCC of the compounds, TiO2, TyzorLA and CeB6, were tested for several types of SG tubing materials. The test with the addition of TiO2 (P25) and CeB6 showed an effect in decreasing the SCC for the SG tubing material. However, CeB6 caused some more SCC for Alloy 800. The penetration property into a crevice of the inhibitors was investigated by using Alloy 600 specimens with different gap sizes and an AES analysis was performed on the oxide layer of the specimen.

Abstract: The stress corrosion cracking (SCC) susceptibility of Alloy 600 MA has been studied in deaerated 0.01 M sodium sulfate (Na2SO4) and sodium thiosulfate (Na2S2O3) solutions at 340°C. Pre-strained reverse U-bend (RUB) specimens are tested using a static-autoclave system. The specimens show an intergranular SCC and a higher resistance to SCC in a Na2S2O3 solution than in a Na2SO4 solution. The results of the deposits and surface analyses by using XRD and SEM/EDS confirm the existence of the sulfides. The SCC of Alloy 600 MA is associated with the reduced sulfur species and protective oxide film properties formed on the alloy surface in the Na2SO4 and Na2S2O3 solutions.