Session: 04-03: SMRs, Advanced Reactors and Fusion

Paper Number: 147502

147502 - Long-Term Corrosion Behavior of Type 316 Stainless Steel Under Nacl-Mgcl2 Eutectic Salt in Molten Salt Thermal Convection Loop (Mstcl)) 

Abstract: 

Molten chloride salt reactor (MCSR) is one of the small modular reactors (SMR) and is being developed at many research groups. Despite the advantages of molten chloride salt as a fuel or a coolant for MCSR, the lack of understanding of the long-term corrosion behaviors of structural material caused by molten chloride salt is an obstacle to the development of MCSR. To investigate the long-term corrosion behavior of candidate structural materials, molten salt thermal convection loop (MSTCL), which consists of a skewed parallelepiped flow path, a hot leg pot, a cold leg pot, a melting pot, and a gas control system, has been used. A type 316 stainless steel has been tested for 10 weeks under NaCl-MaCl₂ eutectic salt. The specimens were placed where the salt temperature was about 570, 550, 540, 525, and 490℃, respectively. The specimens were periodically removed from MSTCL and weighted to measure mass loss by corrosion. Corrosion rate of the type 316 stainless steel was estimated with weight loss of the removed specimens from the MSTCL and showed a linear kinetics for 10 weeks. The specimens located at a higher temperature showed a faster corrosion rate those located at a lower temperature. In particular, the corrosion rate of the specimen located at 570℃ showed a faster corrosion rate over time than other specimens. In the relationship between corrosion rate and temperature, there seems to be a threshold temperature at which the corrosion rate increases significantly, but the threshold temperature could not be specified in the experiment. Surface analysis of the specimens with SEM-EDS showed that Cr and Fe were depleted and Ni, Mo, and C were accumulated at the surface. Cross-sectional image mapping with SEM-EDS of the specimens showed that Fe and Cr were depleted and Mg, a salt component, was penetrated along the grain boundary. Since the oxidation-reduction potential of alloying elements is in the order Mo>Ni>Fe>Cr, Fe and Cr with low oxidation-reduction potential are eluted, and Ni and Mo, which are not eluted, have a relatively high content at the surface. The carbon inside the alloy is one of the elements with a high diffusion coefficient and will diffuse to the surface over time. In this process, Mo, which easily forms carbide, seems to combine with carbon to form molybdenum carbide at the surface. Experimental results of type 316 stainless steel for 10 weeks show that the depletion of Fe and Cr from the alloy matrix is the main corrosion phenomena and a mechanism to suppress the depletion of Fe and Cr was not observed. However, since corrosion test for 10 weeks is a relatively short period to determine the suitability of type 316 stainless steel as a structural material for MCSR, a longer corrosion test will be necessary.

Presenting Author: Byung Gi Park Soonchunhyang University

Presenting Author Biography: Professional Experience
2007.3-present Professor, Department of Energy and Environmental Engineering, Soonchunhyang University, Republic of Korea

Education
Ph.D Department of Nuclear Engineering, Seoul National University (1999)
MS Department of Nuclear Engineering, Seoul National University (1993)
BS Department of Nuclear Engineering, Seoul National University (1990)

Research Interest
Molten Salt Chemistry (Pyroprocessing of Spent Nuclear Fuel), Recycling and Reuse of Spent Nuclear Fuel
Water Chemistry of Nuclear Power Plant

Authors:

Hyunjin Boo Soonchunhyang University
Su Hyun Lee Soonchunhyang University
Byung Gi Park Soonchunhyang University