Analysis of the microstructural evolution of the damage by neutron irradiation in the pressure vessel of a nuclear power reactor BWR

Nuclear reactor pressure vessel type BWR, installed in Mexico and in many other countries, are made of an alloy of low carbon steel. The American Society for Testing and Materials (Astm) classifies this alloy as A533-B, class 1. Both the vessel and other internal structures are continuously exposed to the neutron flux from the reactions of fission in nuclear fuel. A large number of neutrons reach the vessel and penetrate certain depth depending on their energy. Its penetration in the neutron collides with the nuclei of the atoms out of their positions in the crystal lattice of steel, producing vacancies, interstitial, segregations, among other defects, capable of affecting its mechanical properties. Analyze the micro-structural damage to the vessel due to neutron irradiation, is essential for reasons of integrity of this enclosure and safety of any nuclear power plant. The objective of this thesis work is theoretical and experimentally determine the microstructural damage of a type nuclear reactor vessel steel BWR, due to neutron radiation from the reactor core, using microscopic and spectroscopic techniques as well as Monte Carlo simulation. Microscopy Optical, Scanning Electron Microscopy, Transmission Electron Microscopy, Energy Dispersion of X-rays Spectrometry and X-rays Diffractometry were the techniques used in this research. These techniques helped in the characterization of both the basis of design of pressure vessel steel and steel irradiated, after eight years of neutron irradiation on the vessel, allowing know the surface morphology and crystal structures of the previous steel and post-irradiation, analyze the change in the microstructure of the steel vessel, morphological damage to surface level in an irradiated sample, among which are cavities in the order of microns produced by Atomic displacements due to the impact of neutronic, above all in the first layers of thickness of the vessel, the effect of swelling, regions of greater damage and Atomic chemical of steel components concentration profiles after irradiated, among others. MCNPX version 2005 and SRIM-2011 there are the computer codes used in the Monte Carlo simulation for analyzing the vessel damage theoretically due to penetration and the radiation transport of the neutrons coming of the reactor core. With MCNPX was determined the profile of neutrons penetration, the photons flux, electrons, alphas, protons deuterons, etc, in the interior of the vessel, the profile of energy deposited by all particles generated in the interaction of neutrons with the steel atomic structures, the profile displacement, the regions of greater damage as well as the total damage over the life of the reactor, among many others. With SRIM-2011 was determined the atomic displacements profile of each atomic species in the steel (Fe, Ni, Mn, Cr, Mo, V, Cu, etc.), the energy deposited profile by each atomic species, the profile of damage in the interior of the vessel, the greater damage region as well as the total damage throughout the life of the nuclear reactor. The theoretical results have enabled understanding of physical phenomena occurring in the crystalline structure of steel, by influence of irradiation neutron to determine the region of greatest possible damage in the crock. The theoretical results were compared with experimental results and those of international references in this field of research. Among other results, is determined that the region of greater damage occurs in the first millimeter of depth of the vessel and confirms its full integrity after eight years of neutron irradiation and to not less than 60 years of life with a thickness of 12 cm. (Author)