Correlation between Pitch Impregnation Pressure and Pore Sizes of Graphite Block

This study aimed to investigate the effect of impregnation pressure on the decrease in porosity of impregnated bulk graphite. The correlation between pitch impregnation behavior and the pore sizes of the bulk graphite block was studied to determine the optimal impregnation pressure. The densities and porosities of the bulk graphite before and after pitch impregnation under various pressures between 10 and 50 bar were evaluated based on the Archimedes method and a mercury porosimeter. The density increased rates increased by 1.93–2.44%, whereas the impregnation rate calculated from the rate of open porosity decreased by 15.15–24.48%. The density increase rate and impregnation rate were significantly high when the impregnation pressures were 40 and 50 bar. Compared with impregnation pressures of 10, 20, and 30 bar, the minimum impregnatable pore sizes with impregnation pressures of 40 and 50 bar were 30–39 and 24–31 nm, respectively. The mercury intrusion porosimeter analysis results demonstrated that the pressure-sensitive pore sizes of the graphite blocks were in the range of 100–4500 nm. Furthermore, the ink-bottle-type pores in this range contributed predominantly to the effect of impregnation under pressure, given that the pitch-impregnated-into-ink-bottle-type pores were difficult to elute during carbonization.

Approaches to graphite block characterization by gamma radionuclides and their packaging during UGR stack dismantlement

This paper presents technical and methodological approaches developed by PDC UGR to characterize the removed graphite blocks by gamma-emitting radionuclides during graphite stack dismantlement and to enable their packaging. It overviews the experimental testing of the characterization method and its findings. It also presents container design option allowing to achieve the maximum filling efficiency.

Shielding effectiveness measurement of cement-graphite block in between 3.8 GHz to 6 GHz

Due to proliferation of electronic devices, the electromagnetic field (EMF) exposure affect human health in long term. On the other hand the operation electronic devices will be affected if the radiation level is too high. To reduce the radiation exposure, shielding is always used. Instead of building a shielding enclosure inside a building, it is more practical to improve the shielding capability of the building itself. Hence, this project intend to investigate the shielding effectiveness (SE) of cement added with graphite. Eight cement-graphite specimens with different percentages (0%, 3%, 7%, 11%, 15%, 19%, 25% and 30%) are prepared. They have been casted into the waveguide mold with size of 4.75 cm x 1 cm x 2.22 cm and taken for measurement directly. The SE measurement setup involve a pair of waveguide with frequency range of 3.8 GHz to 6 GHz and vector network analyser (VNA). Throughout the study, it is found that the percentage of graphite powder will affect the SE of the specimens. The SE is independent on its curing duration. More than 11% of graphite is needed to improve the SE of cement block in between 3.8 GHz to 6 GHz. The highest SE of 33 dB is achieved when the sample contains 30% of graphite with thickness of 1cm.

EFFECT OF NACL ON NEUTRON FLUX DENSITY IN GRAPHITE BLOCK

Aim of this work is to study the effect of NaCl on neutron flux through graphite block. Graphite block had 39 channels drilled through it and filled with NaCl. Au and In foils and In wire was used for neutron activation measurement of the neutron flux. AmBe neutron source with nominal activity of 92.5 GBq was used. The results were compared with MCNP simulations with channels filled with salt and air. Twelve different locations for Au and In foils were used and In wires were place in three locations to measure vertical profile of neutron flux.