• Nuclear Engineering and Technology
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• v.52 no.3
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• pp.469-476
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• 2020

Research reactors in-core experimental facilities are designed to provide the highest steady state flux for user's irradiation requirements. However, fuel conversion from highly enriched uranium (HEU) to low enriched uranium (LEU) driven by the ongoing effort to diminish proliferation risk, will impact reactor physics parameters. Preserving the reactor capability to produce the needed flux to perform its intended research functions, determines the conversion feasibility. This study investigates the neutron flux in the central experimental facility of two material test reactors (MTR), the IAEA generic10 MW benchmark reactor and the 22 MW s Egyptian Test and Research Reactor (ETRR-2). A 3D full core model with three uranium enrichment of 93%, 45%, and 20% was constructed utilizing the OpenMC particle transport Monte Carlo code. Neutronics calculations were performed for fresh fuel, the beginning of life cycle (BOL) and end of life cycle (EOL) for each of the three enrichments for both the IAEA 10 MW generic reactor and core 1/98 of the ETRR-2 reactor. Criticality calculations of the effective multiplication factor (K_eff) were executed for each of the twelve cases; results show a reasonable agreement with published benchmark values for both reactors. The thermal, epithermal and fast neutron fluxes were tallied across the core, utilizing the mesh tally capability of the code and are presented here. The axial flux in the central experimental facility was tallied at 1 cm intervals, for each of the cases; results for IAEA 10 MW show a maximum reduction of 14.32% in the thermal flux of LEU to that of the HEU, at EOL. The reduction of the thermal flux for fresh fuel was between 5.81% and 9.62%, with an average drop of 8.1%. At the BOL the thermal flux showed a larger reduction range of 6.92%-13.58% with an average drop of 10.73%. Furthermore, the fission reaction rate was calculated, results showed an increase in the peak fission rate of the LEU case compared to the HEU case. Results for the ETRR-2 reactor show an average increase of 62.31% in the thermal flux of LEU to that of the HEU due to the effect of spectrum hardening. The fission rate density increased with enrichment, resulting in 34% maximum increase in the HEU case compared to the LEU case at the assemblies surrounding the flux trap.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.1
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• pp.1-7
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• 1999

In order to determine the mode I stress intensity factor ($K_I$) by means of the alternating current potential drop(ACPD) technique, the change in potential drop due to load for a paramagnetic material containing a two-dimensional surface crack was examined. The cause of the change in potential drop and the effects of the magnetic flux and the demagnetization on the change in potential drop were clarified by using the measuring systems with and without removing the magnetic flux from the circumference of the specimen. The change in potential drop was linearly decreased with increasing the tensile load and was caused by the change in conductivity near the crack tip. The reason of decreasing the change in potential drop with increasing the tensile load was that the increase of the conductivity near the crack tip due to the tensile load caused the decreases of the resistance and internal inductance of the specimen The relationship between the change in potential drop and the change in $K_I$ was not affected by demagnetization and was independent of the crack length.

• Korean Journal of Materials Research
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• v.23 no.5
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• pp.293-298
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• 2013

In this study, an HP-mod. type(KHR-45A), which is used as a heater tube material in the pyrolysis process, was evaluated for its carburizing properties. It was confirmed from the microstructural observation of the tubes that the volume fraction of carbide increased and that the coarsening of Cr-carbide generated as a degree of carburization increased. The depth of the hardened layer, which is similar to the thickness of the carburized region of each specimen, due to carburization is confirmed by measurement of the micro-Vickers hardness of the cross section tube, which thickness is similar to that of the carburized region of each specimen. Two types of chromium carbides were identified from the EBSD (electron back-scattered diffraction) image and the EDS (energy-dispersive spectroscopy) analysis: Cr-rich $M_{23}C_6$ in the outer region and Cr-rich $M_7C_3$ in the inner region of tubes. The EDS analysis revealed a correlation between the ferromagnetic behavior of the tubes and the chromium depletion in the matrix. The chromium depletion in the austenite matrix is the main cause of the magnetization of the carburized tube. The method used currently for the measurement of the carburization of the tubes is confirmed; carburizing evaluation is useful for magnetic flux density measurement. The volume fraction of the carbide increased as the measuring point moved into the carburized side; this was determined from the calculation of the volume fraction in the cross-section image of the tubes. These results are similar to the trends of carburization measurement when those trends were evaluated by measurement of the magnetic flux density.

• Membrane Journal
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• v.25 no.6
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• pp.538-546
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• 2015

In this study, composite membrane is prepared by Layer-by-Layer method using hydrophobic polymer as a coating material on the polysulfone support. The existence of coating layer on the surface and cross section was confirmed by the scanning electronic microscopy. The flux and rejection of the resulting membranes were characterized using 100 ppm NaCl feed solution. PVSA, PEI, PAA, PSSA, PSSA_MA were used as a coating polymer in this study. The composite membrane prepared by using 8,000 ppm PAA solution (Ion strength = 0.35, Coating time = 3 min) and 10,000 ppm PEI solution (Coating time = 4 min). As a result, PAA-PEI composite membrane showed flux of 101 LMH and salt rejection of 66.7%. The composite membrane showed the comparable performance as good as NE 4040-70 (Flux = 30 LMH, Rejection = 40~70%) model produced by Toray Chemical co.

• Journal of the Korean Magnetics Society
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• v.11 no.3
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• pp.134-140
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• 2001

Flux-gate magnetometer was developed in 1930's, and it has been widely used for the low magnetic field measurements. In this work, we have employed amorphous ribbon 2714A produced by Allied Chem. Co. as sensor core material. To develop low noise, low power consumption, and high reliability flux-gate magnetometer, we have measured ac magnetic properties depending on the annealing conditions. As quenched state amorphous core shows high noise level and ac magnetic properties were changed under the condition of accelerated aging test, but amorphous ribbon, which was annealed under 350 $\^{C}$ during 1 hour, shows low noise level of 0.1 nT in the frequency range of dc∼10 Hz which was 10 times better than the as quenched amorphous ribbon. Under accelerated aging test, ac magnetic properties such as squareness and coercivity of the annealed samples show higher reliability and approached to a certain limiting value as exponential function. We can see that high reliability and low noise flux-gate magnetometer could be developed, if we consider this ac magnetic properties change in the sensor design.

• Korean Journal of Materials Research
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• v.18 no.2
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• pp.77-83
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• 2008

Green-emitting $Ba_{1.468}Sr_{0.5}SiO_4\;:\;Eu_{0.012},\;Y_{0.02}$ phosphor powders under long-wavelength ultraviolet light were prepared via high-temperature flame spray pyrolysis from spray solutions with and without $NH_4Cl$ flux. The effects of the temperature of the diffusion flame and the $NH_4Cl$ flux on the morphologies, crystal structures and photoluminescence intensities of the $Ba_{1.468}Sr_{0.5}SiO_4\;:\;Eu_{0.012},\;Y_{0.02}$ phosphor powders were investigated. The phosphor powders obtained from the spray solution with the $NH_4Cl$ flux had higher photoluminescence intensities compared to phosphor powders obtained from the spray solution without the flux. The photoluminescence intensity of the phosphor powders obtained from the spray solution without the flux decreased as the flow rate of the fuel gas increased. On the other hand, the photoluminescence intensity of the phosphor powders obtained from the spray solution with the flux increased as the flow rate of the fuel gas increased. The difference of in the phase purity and morphology of the powders affected the photoluminescence intensities of the phosphor powders.

• Journal of the Korean Society of Radiology
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• v.11 no.4
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• pp.197-203
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• 2017

This study purpose is propose the basic data for selecting the optimal target material by analyzing the photon characteristics of various materials which was located in the head of medical linear accelerator. In this study, energy spectrum of 6, 15 MV photon beams were compared and analyzed for 13 target materials using MCNPX of Monte Carlo method. The mean energy for the 6 MV energy spectrum was 1.69 ~ 1.84 MeV and that for the 15 MV was 3.38 ~ 3.56 MeV, according to the target material. The flux for the 6 MV energy spectrum was $1.64{\times}10^{-5}{\sim}1.80{\times}10^{-5}{\sharp}/cm^2/e$ and that for the 15 MV was $1.76{\times}10^{-4}{\sim}1.85{\times}10^{-4}{\sharp}/cm^2/e$. The analysis shows that the average energy and flux increase with higher atomic number of the target material. Based on this study, it is possible to present the basic data about the physical characteristics of the photon, and it will be possible to select the target later considering economic, efficiency and physical aspect.

• Korean Chemical Engineering Research
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• v.46 no.6
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• pp.1075-1080
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• 2008

Fine-sized $Gd_2O_3:Eu$ phosphor powders were prepared by post-treatment of the precursor powders with hollow shape obtained by spray pyrolysis from the spray solution with citric acid and flux material. Citric acid enabled the synthesis of fine-sized phosphor powders after post-treatment by increasing the hollowness of the precursor powders. The phosphor powders prepared from the spray solution without citric acid had several microns size. Flux materials increased the mean sizes of the phosphor powders. However, flux materials improved the photoluminescence intensities of the phosphor powders under ultraviolet. $Li_2CO_3$ as the flux material was appropriate to prepare the fine-sized $Gd_2O_3:Eu$ phosphor powders with high photoluminescence intensity. The phosphor powders below 3 wt% $Li_2CO_3$ of phosphor had submicron sizes after post-treatment temperatures of $1,050^{\circ}C$ and $1,150^{\circ}C$. The photoluminescence intensity of the phosphor powders post-treated at $1,150^{\circ}C$ was 124% of that of the phosphor powders post-treated at $1,050^{\circ}C$.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.3
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• pp.207-214
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• 2005

After more than 100 years of development, rotating electric machines are a mature industrial product. Nevertheless, improvements are still possible for specific applications, and it is likely that the major evolution will be promoted by new materials and unconventional structures. Till now, plastic materials are an infrequent choice for the electric machines structural parts, but pioneering applications, such as aeronautical components, let some technological scouting: a low-weight/high-efficiency plastic axial flux motor for a solar flying platform is presented as an example of combined new-material/new-geometry development. The basic design aspects and the prototyping choices are presented and discussed together with the first experimental results.

• Journal of Powder Materials
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• v.13 no.3 s.56
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• pp.217-222
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• 2006

The relationship between electrical properties of superconductor and externally applied magnetic field was studied to develop a magnetic field sensor. The electrical resistance of the superconductor was increased by applying external magnetic field and even after removal of the magnetic field. This behavior was related to the magnetic flux trapped in the superconductor, which penetrated through the material by the external magnetic field. Some portion of the superconductor was changed to a normal state by the trapped magnetic flux. The appearance of the normal state yielded to enhance the electrical resistance.