Characterization of 14C in neutron irradiated NBG-25 nuclear graphite

Identification and location of 14C-bearing species in thermally treated neutron irradiated graphites NBG-18 and NBG-25: Pre- and post-thermal treatment

“…Comparison of surface and subsurface speciation of irradiated NBG-25 using SIMS revealed that the largest concentration of 14 C-bearing species, with few notable exceptions, was located within the first few nanometers of surface material [3]. The results for irradiated NBG-18 are consistent with this finding (Table 7).…”

“…Nitrogen was not detected on the surface of irradiated NBG-25; upon delving further beneath the surface using a focused ion beam (FIB) device, clusters of nitrogen were discovered embedded within an apparent closed pore within an irradiated NBG-25 sample (Fig. 4, right) [3]. These clusters of nitrogen are not observed via SEM in thermally treated NBG-18 and NBG-25 samples (Fig.…”

“…7, Table 3) is presented below. The authors attributed the inflated concentration of nitrogen at these depths to the migration of surface nitrogen deeper into the graphite via openings in the graphite lattice produced by neutron bombardment [3].…”

A Study of the Oxidation Behaviour of Pile Grade A (PGA) Nuclear Graphite Using Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and X-Ray Tomography (XRT)

“…This slow oxidation rate allows diffusion of gases throughout the graphite and deep into the pore network, effectively oxidising the graphite from the exposed outer surface of not only the external surface but also the pore surfaces. This is critical for studying 14 C concentrations as this radioisotope may not be homogeneously distributed throughout the graphite as 14 C formed from 14 N or 1 O from the coolant gas may be more localised on the pore surface whereas 14 C from 13 C and 14 N found in the graphite lattice will be evenly distributed and also be bonded differently [ 49 ]. LaBrier and Dunzik-Gougar [ 49 ] studied NBG-25 graphite that had been irradiated in a test reactor at the Idaho National Laboratory.…”

“…This is critical for studying 14 C concentrations as this radioisotope may not be homogeneously distributed throughout the graphite as 14 C formed from 14 N or 1 O from the coolant gas may be more localised on the pore surface whereas 14 C from 13 C and 14 N found in the graphite lattice will be evenly distributed and also be bonded differently [ 49 ]. LaBrier and Dunzik-Gougar [ 49 ] studied NBG-25 graphite that had been irradiated in a test reactor at the Idaho National Laboratory. Time-of-Flight Secondary Ion Mass Spectrometry and X-Ray Photoelectron Spectroscopy showed that 14 C exists predominantly on or near the surface.…”