• Nuclear Engineering and Technology
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• v.21 no.1
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• pp.12-17
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• 1989

The correction factor of neutron fraction absorbed by $^{55}$ Mn in the MnSO$_4$ bath was determined for the absolute measurement of neutron emission rate by using the solution circulation-type manganese sulfate bath system. For the determination of this correction factor, I/f, the atomic number desnsity and the effective neutron capture cross section data of Mn, S and impurity elements in the MnSO$_4$ solution were determined. For the atomic number density determination, the MnSO$_4$ solution concentration was determined by using the volumetric EDTA titration and gravimetric method. The impurity contents were analyzed by using the ICP method. For the calculation of effective neutron capture cross sections, a FORTRAN computer program EASCAL was developed in this study. in which Westcott's parameters and Axton's empirical relations are used.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1763-1774
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• 2023

In this study, a series of flexible neutron/gamma shielding composites are fabricated through the doping of Gd₂O₃ into the matrix of SEBS with (M_Gd2O3: M_SEBS) % from 5% to 100%. Neutron transmittance test shows an exponential attenuation with the increase of areal density of Gd, in which the transmittance T ranges from 59.1440% to 35.3026%, with standard deviation less than 2.2743%, mass attenuation coefficient 𝜇_m from 0.3194 cm²/g to 0.4999 cm²/g, and half value layer-HVL value from 2.4530 mm to 1.1313 mm. Shielding efficiency of the Gd₂O₃/SEBS composites is basically improved in comparison with that of B₄C/SEBS. The transmittance T, mass/linear attenuation coefficient 𝜇_m and 𝜇, HVL and effective atomic number Z_eff for the shielding of γ rays (39 keV, 59 keV and 122 keV) are measured and calculated with XCOM as well as MCX programs. Finally, plots of the three dimensional relationships between transmittance, doping amount and thickness are provided to the guidance for engineering shielding design. In summary, the Gd₂O₃/SEBS composite is proved to be an effective flexible neutron/low energy γ rays shielding material, which could be of potential applications in the field of nuclear technology and nuclear engineering.

• 한국초전도학회:학술대회논문집
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• 2009.07a
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• pp.5-5
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• 2009

• 한국지구물리탐사학회:학술대회논문집
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• 2011.10a
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• pp.99-100
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• 2011

• Journal of Powder Materials
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• v.20 no.2
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• pp.142-147
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• 2013

$YBa_2Cu_3O_{7-y}$ (Y123) powders for the fabrication of bulk superconductors were synthesized by the powder reaction method using $Y_2O_3$ (99.9% purity), $BaCO_3$ (99.75%) and CuO (99.9%) powders. The raw powders were weighed to the cation ratio of Y:Ba:Cu=1:2:3, mixed and calcined at $880^{\circ}C-930^{\circ}C$ in air with intermediate repeated crushing steps. It was found that the formation of Y123 powder was more sensitive to reaction temperature than reaction time. The calcined Y123 powder and a mixture of (Y123 + 0.25 mole $Y_2O_3$ + 1 wt.% $CeO_2$, $Y_{1.5}Ba_2Cu_3O_x$ (Y1.5)) were used as raw powders for the fabrication of poly-grain or single grain superconductors. The superconducting transition temperature ($T_{c,onset}$) of the sintered Y123 sample was 91 K and the transition width was as large as 11 K, whereas the $T_{c,onset}$ of the melt-grown Y1.5 sample was 90.5 K and the transition width was 3.5 K. The critical current density ($J_c$) at 77 K and 0 T of the sintered Y123 was 700 $A/cm^2$, whereas the $J_c$ of the top-seeded melt growth (TSMG) processed Y1.5 sample was $3.2{\times}10^4\;A/cm^2$. The magnetic flux density (H) at 77 K of the TSMG-processed Y123 and Y1.5 sample showed the 0.53 kG and 2.45 kG, respectively, which are 15% and 71% of the applied magnetic field of 3.5 kG. The high H value of the TSMG-processed Y1.5 sample is attributed to the formation of the larger superconducting grain with fine Y211 dispersion.

• Korean Journal of Materials Research
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• v.23 no.6
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• pp.309-315
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• 2013

$GdBa_2Cu_3O_{7-y}$(Gd123) powders were synthesized by the solid-state reaction method using $Gd_2O_3$ (99.9% purity), $BaCO_3$ (99.75%) and CuO (99.9%) powders. The synthesized Gd123 powder and the Gd123 powder with $Gd_2O_3$ addition ($Gd_{1.5}Ba_2Cu_3O_{7-y}$(Gd1.5)) were used as raw powders for the fabrication of Gd123 bulk superconductors. The Gd123 and Gd1.5 bulk superconductors were fabricated by sintering or a top-seeded melt growth (TSMG) process. The superconducting transition temperature ($T_{c,onset}$) of the sintered Gd123 was 93 K and the transition width was as large as 20 K. The $T_{c,onset}$ of the TSMG processed Gd123 was 82 K and the transition width was also as large as 12 K. The critical current density ($J_c$) at 77 K and 0 T of the sintered Gd123 and TSMG processed Gd123 were as low as a few hundreds A/$cm^2$. The addition of 0.25 mole $Gd_2O_3$ and 1 wt.% $CeO_2$ to Gd123 enhanced the $T_c$, $J_c$ and magnetic flux density (H) of the TSMG processed Gd123 sample owing to the formation of the superconducting phase with high flux pinning capability. The $T_c$ of the TSMG processed Gd1.5 was 92 K and the transition width was 1 K. The $J_cs$ at 77 K (0 T and 2 T) were $3.2{\times}10^4\;A/cm^2$ and $2.5{\times}10^4\;A/cm^2$, respectively. The H at 77 K of the TSMG-processed Gd1.5 was 1.96 kG, which is 54% of the applied magnetic field (3.45 kG).

• Korean Journal of Materials Research
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• v.22 no.11
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• pp.569-574
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• 2012

Large single grain $Gd_{1.5}Ba_2Cu_3O_{7-y}$ (Gd1.5) bulk superconductors were fabricated by a top-seeded melt growth (TSMG) process using an $NdBa_2Cu_3O_{7-y}$ seed. The seeded Gd1.5 powder compacts with a diameter of 50 mm were subjected to the heating cycles of a TSMG process. After the TSMG process, the diameter of the single grain Gd1.5 compact was reduced to 43 mm owing to the volume contraction during the heat treatment. The superconducting transition temperature ($T_c$) of the top surface of the single grain Gd1.5 sample was as high as 93.5 K. The critical current densities ($J_cs$) at 77 K and 1T and 1.5 T were in ranges of 25,200-43,900 $A/cm^2$ and 10,000-23,000 $A/cm^2$, respectively. The maximum attractive force at 77 K of the sample field-cooled using an Nd-B-Fe permanent magnet (surface magnetic field of 0. 527 T) was 108.3 N; the maximum repulsive force of the zero field-cooled sample was 262 N. The magnetic flux density of the sample field-cooled at 77 K was 0.311T, which is approximately 85% of the applied magnetic field of 0.375 T. Microstructure investigation showed that many $Gd_2BaCuO_5$ (Gd211) particles of a few ${\mu}m$ in size, which are flux pinning sites of Gd123, were trapped within the $GdBa_2Cu_3O_{7-y}$ (Gd123) grain; unreacted $Ba_3Cu_5O_8$ liquid and Gd211 particles were present near the edge regions of the single grain Gd1.5 bulk compact.

• Nuclear Engineering and Technology
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• v.52 no.11
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• pp.2415-2421
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• 2020

The axial heterogeneous void distribution in a fuel channel is a relevant and important issue during nuclear reactor analysis for LWR, especially for boiling water channel-type reactors. Variation of the coolant density in fuel channel has an effect on the neutron spectrum that will in turn have an impact on the values of absolute reactivity, the void reactivity coefficient, and the fuel isotopic compositions during irradiation. This effect is referring to as the history effect in light water reactor calculations. As the void reactivity effect is positive in RBMK type reactors, the underestimation of water density heterogeneity in 3D reactor core numerical calculations could cause an uncertainty during assessment of safe operation of nuclear reactor. Thus, this issue is analysed with different cross-section libraries which were generated with WIMS8 code at different reference water densities. The libraries were applied in single fuel model of the nodal code of QUABOX-CUBBOX/HYCA. The thermohydraulic part of HYCA allowed to simulate axial water distribution along fuel assembly model and to estimate water density history effect for RBMK type fuel.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.1
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• pp.188-195
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• 2002

To investigate the degradation of mechanical properties induced mainly by neutron irradiation, the tensile tests were conducted from room temperature to 300\\`c using the irradiated and the unirradiated Zr-2.5Nb pressure tube materials. The irradiated longitudinal and transverse specimens were collected from the coolant inlet, middle, and outlet parts of M-11 tube which had been operated in Wolsung CANDU Unit-1 and exposed to different operating temperatures and irradiation fluences. The different tensile behavior was characterized not by the fluences of irradiation but by the tensile loading direction. The transverse specimen showed the higher strength and lower elongation than those of the longitudinal one. It was believed that these phenomena resulted from the microstructure anisotropy caused by the extrusion process. The increased strength hardening and decreased elongation embrittlement of the irradiated material were compard to those of the unirradiated one. While the tensile strength of the inlet was higher than that of the outlet, the elongation of the inlet was lower than that of outlet. Considering the operation condition, it was proposed that the operating temperature could be a more effective parameter than the irradiation fluence for long-time life. Through the TEM observation, it was found that while the a-type dislocation density was increased, the c-type dislocation was not changed in the irradiated. The fact that the higher dislocation density was sequentially distributed over the inlet, the middle, and the outlet parts was consistent with the distribution of the tensile strength.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.21-21
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• 2011

A series of Quasi-Elastic Neutron Scattering (QENS) experiments helps us to understand the single-particle (hydrogen atom) dynamics of a globular protein and its hydration water and strong coupling between them. We also performed Molecular Dynamics (MD) simulations on a realistic model of the hydrated hen-egg Lysozyme powder having two proteins in the periodic box. We found the existence of a Fragile-to-Strong dynamic Crossover (FSC) phenomenon in hydration water around a protein occurring at TL=$225{\pm}5K$ by analyzing Intermediate Scattering Function (ISF). On lowering of the temperature toward FSC, the structure of hydration water makes a transition from predominantly the High Density Liquid (HDL) form, a more fluid state, to predominantly the Low Density Liquid (LDL) form, a less fluid state, derived from the existence of a liquid?liquid critical point at an elevated pressure. We showed experimentally and confirmed theoretically that this sudden switch in the mobility of the hydration water around a protein triggers the dynamic transition (so-called glass transition) of the protein, at a temperature TD=220 K. Mean Square Displacement (MSD) is the important factor to show that the FSC is the key to the strong coupling between a protein and its hydration water by suggesting TL${\fallingdotseq}$TD. MD simulations with TIP4P force field for water were performed to understand hydration level dependency of the FSC temperature. We added water molecules to increase hydration level of the protein hydration water, from 0.30, 0.45, 0.60 and 1.00 (1.00 is the bulk water). These confirm the existence of the FSC and the hydration level dependence of the FSC temperature: FSC temperature is decreased upon increasing hydration level. We compared the hydration water around Lysozyme, B-DNA and RNA. Similarity among those suggests that the FSC and this coupling be universal for globular proteins, biopolymers.