Characterization of oxide layers grown on D9 austenitic stainless steel in lead bismuth eutectic

Lead bismuth eutectic (LBE) is a possible coolant for fast reactors and targets in spallation neutron sources. Its low melting point, high evaporation point, good thermal conductivity, low reactivity, and good neutron yield make it a safe and high performance coolant in radiation environments. The disadvantage is that it is a corrosive medium for most steels and container materials. This study was performed to evaluate the corrosion behavior of the austenitic stainless steel D9 in oxygen controlled LBE. In order to predict the corrosion behavior of steel in this environment detailed analyses have to be performed on the oxide layers formed on these materials and various other relevant materials upon exposure to LBE. In this study the corrosion/oxidation of D9 stainless steel in LBE was investigated in great detail. The oxide layers formed were characterized using atomic force microscopy, magnetic force microscopy, nanoindentation, and scanning electron microscopy with wavelength-dispersive spectroscopy (WDS) to understand the corrosion and oxidation mechanisms of D9 stainless steel in contact with the LBE. What was previously believed to be a simple double oxide layer was identified here to consist of at least 4 different oxide layers. It was found that the inner most oxide layer takes over the grain structure of what used to be the bulk steel material while the outer oxide layer consists of freshly grown oxides with a columnar structure. These results lead to a descriptive model of how these oxide layers grow on this steel under the harsh environments encountered in these applications.

The measurements of neutron and gamma dose rates in mixed radiation fields, using a liquid scintillation counter

Measurements of neutron and gamma dose rates in mixed radiation fields, and gamma dose rates from calibrated gamma sources, were performed using a liquid scintillation counter NE213 with a pulse shape discrimination technique based on the charge comparison method. A computer program was used to analyse the experimental data. The radiation field was obtained from a 241Am-9Be source. There was general agreement between measured and calculated neutron and gamma dose rates in the mixed radiation field, but some disagreement in the measurements of gamma dose rates for gamma sources, due to the dark current of the photomultiplier and the effect of the perturbation of the radiation field by the detector. An optical fibre bundle was used to couple an NE213 scintillator to a photomultiplier, in an attempt to minimise these effects. This produced an improvement in the results for gamma sources. However, the optically coupled detector system could not be used for neutron and gamma dose rate measurements in mixed radiation fields. The pulse shape discrimination system became ineffective as a consequence of the slower time response of the detector system.