The corrosion process which steels go through by exposure to Lead-Bismuth Eutectic (LBE) is of major concern in many nuclear energy applications. LBE has been used as a coolant in nuclear reactors for several decades. LBE has been prosposed as the coolant material and spallation target in project proposed by the Department of Energy (DOE) - Accelerator Transmutation of Waste (ATW). In ATW, ~1 GeV protons strike a spallation target, producing high fluxes of neutrons that can be used to bombard nuclear waste, converting them to isotopes of much shorter halflife. This project is under study by the DOE because of its possible solutions to nuclear waste disposal and hence, the possible resurgence of nuclear power.
What makes LBE a good coolant is its thermal properties. LBE has a boiling point over 1200°C and melting point of 130°C, which is a temperature range that more than covers the range needed. Moreover, it can be easily kept in a liquid phase ( >180°C) through the use of steam heating. What makes it a good candidate as a spallation target is the heavy nuclei of lead (~207 amu) and bismuth (~209 amu). The accelerated protons have a higher probability of knocking out neutrons in elements that have heavy atomic masses because there are many neutrons present, making for large collisional cross sections.
One problem with LBE is that it is known to cause rapid and significant corrosion on structural steels. It has been learned through experiment that flowing a small amount of oxygen in the LBE significantly reduces the rate of corrosion. However, the corrosion mechanism from LBE in contact with steel is not well understood. By investigating steel samples that have been exposed to LBE for certain numbers of hours and at different temperatures, it is hoped that this process will be better understood and results could lead to further advancement in ATW. The samples are steel rods and tubes, provided by Dr. Ning Li at Los Alamos National Lab (LANL). We plan on exploiting a number of surface chemistry techniques to obtain data on the steel samples.
One technique is Electron Microprobe Analysis (EPMA). Using the Scanning Electron Microscope (SEM) in The Department of Geosciences at UNLV, detailed images of the surfaces provide information on surface morphology. Also, as a biproduct of keV electron bombardment, keV x-rays are produced that can be analyzed to provide elemental finger printing as a function of position on the surfaces.
Another technique to be is used is X-Ray Photoelectron Spectroscopy (XPS). In XPS, electrons are photoemitted from atomic core levels by use of x-rays. The electrons are detected as a function of energy, providing information on the chemical environment of the atoms. A XPS apparatus is in operation at the Desert Research Institute (DRI), adjacent to UNLV.
A third technique is X-Ray Diffraction (XRD). By scraping small amounts off the steel surfaces into a powder, they can be irradiated with x-rays to produce diffraction patterns. Analysis of diffraction patterns is yet another way of identifying elemental crystal structures. There is an X-Ray Diffractometer in the lab of Dr. Malcolm Nicol in the UNLV Physics department.