CORROSION STUDY OF STEELS IN LIQUID LEAD-BISMUTH COOLED NUCLEAR REACTORS USING MOLECULAR DYNAMICS

• Main Author: Maulana, Alan
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/72989
• Institution: Institut Teknologi Bandung

Pb-Bi cooled Nuclear reactors are among the most prospective Generation-IV nuclear reactors which have inherent safety capability, economical, and able to burn their own nuclear waste. However, the steel corrosion in the interaction with liquid lead-bismuth is still being a problem to be solved. Therefore this dissertation investigates steel corrosion in liquid Pb-Bi problem using molecular dynamic program called Moldy which used to simulate the interaction between surfaces of Fe system with Pb-Bi. This work is an effort to understand the corrosion phenomena of steels in liquid Pb-Bi at high temperature. Steels and liquid Pb-Bi are important materials in the nuclear fast breeder reactor. Many investigation of steel corrosion phenomena in liquid Lead-Bismuth have been done experimentally, but the interaction mechanism of this material has not been understood yet. Therefore inter-atomic interaction between atoms which involved in the system will be studied. The diffusion processes among atoms are the key issues to understand the corrosion mechanism microscopically. In this simulation interatomic potential between Pb-Pb, Bi-Bi, Fe-Fe, Cr-Cr and Ni-Ni are assumed to follow a Lennard-Jones potential model. The Lennard-Jones potential parameters have been derived by fitting the data available in the literature. Beeman algorithm had been used to calculate the equation of motion. Cell List method had also been involved in order to accelerate the calculation and execution of the program. The structure of simulation cell for Fe and Pb system are BCC (Body Center Cubic) and FCC (Face Center Cubic) respectively. The simulation cells of Fe and Pb were filled by 2000 atoms and 864 atoms, correspondingly. Some of impurities were substituted into the simulation cell above to construct a model of SS 316 (stainless steel 316) and Pb-Bi eutectic. The initial velocity was generated randomly and the temperature system was set using Nose-Hoover thermostat. The molecular dynamic simulation result of pure Fe and Pb system at 1mK showed that the peaks positions of radial distribution function is in a good agreement with the theoretical result. The deviations of the peaks position which were resulted from simulation and experiment for Fe and Pb system are 0.50% and 0.66%, respectively. The simulations also show the broadening of the curves of radial distribution function and lowering the intensity at high temperature. This result indicates that the atomic positions of the system are distributed randomly. The molecular dynamic simulations result of contact between surface of pure Fe and Pb system at 773 K show that no penetration of Pb’s atom into Fe system. This phenomena is caused by the highly of the interaction potential of Fe-Fe. The atomic arrangement of Pb system at these temperatures are random because the system in the liquid phase. Meanwhile, the simulation result of contact between Fe-10%Ni, Fe-16%Cr and Fe-10%Ni-16%C with Pb system at 773 K show that Pb atoms diffuse into Fe system. The penetration of Pb atoms into Fe system indicates that the corrosion is occurred at this temperature. In addition to the above simulations, contact between surfaces of Fe system with Pb-Bi system also is carried out as a function temperature. The composition of Pb- Bi are 50%Pb-50%Bi and 45%Pb-55%Bi and the Fe system used in this simulation are Fe-10%Ni-16%Cr which is an approximation model for SS 316. The molecular dynamic simulation result show that Pb and Bi atoms can diffuse into Fe system. The penetration depth of these atoms increased with the increasing of temperature. These phenomena were occurred for both composition of Pb-Bi. Moreover, we also have simulated Fe system with various compositions of chromium atoms which were contacted into 45%Pb-55%Bi. The result of these simulations at 773 K showed that the lowest penetration depth of Pb and Bi into Fe systems were 16% and 15% respectively.