Jong Kyung Kim

Properties of ZnSe:Te,O Crystals Grown by Bridgman-Stockbarger Method

Zinc selenide crystals were grown in graphite crucibles by the Bridgman–Stockbarger method in a vertical compression furnace under argon pressure of 5×106 Pa. From the absorption spectra, the band gap energies of the ZnSe single crystals were calculated by a linear fitting process. The maximum wavelength of the emission spectrum of the ZnSe:Te,O scintillator was 630 nm, which was well matched with the response wavelength of the Si photodiode. The energy resolution of the ZnSe:Te,O scintillator was 11.9% when it was exposed to 137Cs γ-ray. Its size was 10×10×1 mm3. The afterglow level of the ZnSe:Te,O scintillator after 5 ms was 0.023%. The relative light output of the ZnSe:Te,O scintillator was 2.167 times higher than CsI:Tl. The luminescence decay time of the ZnSe:Te,O scintillator has two exponential components with 27 and 84 γs time constant.

A New GUI Based Patient-Specific Treatment Planning System for Boron Neutron Capture Therapy

A new patient-specific treatment planning system, called BTPS, was developed for Boron Neutron Capture Therapy (BNCT). To facilitate planning BNCT, the BTPS was designed through overall planning procedures based on a user-friendly graphical user interface (GUI). A dose calculation engine based on MCNPX was embedded in the BTPS. An accelerated tally technique in MCNP and a parallel computing system to significantly reduce the computation time are also employed. To investigate the performance of the BTPS, computation times for calculating the absorbed dose in a voxel head phantom were evaluated according to the number of computers. To assess the results from the BTPS, thermal neutron fluxes and absorbed doses in a rectangular phantom were calculated and compared with those obtained by using the SERA. The differences in the thermal neutron fluxes and absorbed doses calculated by using BTPS and SERA were 4.3% and 3.8%, respectively, in root mean square. The BTPS facilitates planning of patient-specific BNCT treatments with easy manipulation, and the absorbed dose in the phantom can be calculated with the efficient computation time and good accuracy comparable to that of SERA. Therefore, it is noted that the BTPS is clinically superior to treatment planning systems of BNCT, and allows non-MCNP users to plan easily optimized BNCT treatment.

Development of a High Pressure Xe Ionization Chamber for Environmental Radiation Spectroscopy

A High Pressure Xenon ionization chamber is a promising radiation detector for environmental radiation measurement due to its radiation hardness, its physical rigidity, and its capability of operation at a high temperature up to about 170 °C. A cylindrical high pressure xenon ionization chamber, which was configured with a shielding mesh to improve its energy resolution, was designed on the basis of an electron transfer simulation code (EGSnrc) to extract an optimal density of Xe gas and a thickness of the chamber wall. An electron drift simulation code, Garfield, which was coupled with a Maxwell electric filed calculator, was also employed for the electron drift simulations due to the geometry of the shielding mesh. Shielding inefficiency was also calculated. A spherical ionization chamber was also designed and fabricated to monitor environmental radiation. A noble gas system was constructed to create a noble gas with a high purity and to inject the noble gas up to 60 atm. The combination of an oxygen absorbent (Oxisorb), a molecular sieve, and a high temperature getter can minimize the electro-negative impurities, such as the O2 and N2 gas, to below about several ppb levels. Preliminary tests such as leakage currents, saturation currents, and gas leak test were performed. The performance of the two fabricated ionization chambers at a low dose rate was tested by using a conventional shadow technique with a NIST certified 33.52 MBq 226Ra source in the calibration room at KAERI.

Analysis of Cell Configuration Effects on Nuclear Characteristics in a Lead-Bismuth Cooled Core for TRU Incineration

Sensitivity of the core characteristics to the fuel pin cell parameters change is analyzed for a lead-bismuth cooled reactor to incinerate transuranic nuclides. The pitch-to-diameter ratio is changed for a parametric study to investigate the effects of the coolant-to-fuel ratio. Not only the Zr-based fuel of TRU+Zr but also the Th-based fuel of TRU+Th+Zr is considered in order to investigate the sensitivity of nuclear characteristics of the fuel pin cell to neutron energy spectrum as well as effects of the fuel type on the core performance. For the sensitivity analyses, the neutron spectrum, the criticality performance parameters, and the non-fissile actinides destruction factor are evaluated. The obtained results clarify the unique property of nuclear characteristics of the fuel pin cell and give some useful information for design optimization of a lead-bismuth cooled reactor for TRU transmutation.

A Comparison of Design Study between Critical and Subcritical Systems for TRU Transmutation: Focused on the Safety Point of View

Abstract Currently, two systems for TRU (transuranics) transmutation, the critical and the subcritical reactor systems, are being investigated by many research groups. Both systems have their own advantages and disadvantages. In this study, the comparative analyses of nuclear characteristics between both systems were performed. The fuel loaded into a TRU transmutation reactor includes few fertile nuclides, which contribute to stability and safety of the nuclear reactor. Thus, this study was focused on the intrinsic difference in the dynamic parameters between both systems. At the same time, the neutronic effects of the external source and the neutron absorber on the nuclear characteristics were also analyzed for the subcritical and the critical systems, respectively. Neutron flux spectrum, fuel temperature coefficient, coolant temperature coefficient, delayed neutron fraction, and neutron generation time were considered for comparative analyses. Based on the obtained results, some conclusions and proposals could be derived with relation to TRU transmutation reactor design.

External Source Neutron Effects on the Sensitivity of Subcritical Core Characteristics to Fuel Composition for TRU Transmutation

A subcritical reactor for TRU (Transuranics) transmutation, HYPER (HYbrid Power Extraction Reactor), is under development at KAERI (Korea Atomic Energy Research Institute). For the HYPER system, a pyrochemical process is being considered for fuel reprocessing, due to its own characteristics of nuclear proliferation resistance. Separated from the partitioning process, the fuel contains not only TRU but also the considerable percentages of impurities such as uranium and lanthanides. In our previous studies, the eigen mode calculation had been performed without the external source effects, for the purpose of analyzing the fuel composition effects on the HYPER core characteristics. And the results had shown that the dynamic behavior of the HYPER system becomes unstable as the amount of impurities increases. In this paper, the external source neutron effects on the core characteristics sensitivity to the fuel composition were investigated. Assuming various recovery factors of uranium and lanthanides, some dynamics characteristics as well as the neutron multiplication were evaluated with the source mode calculation and compared with the results of the eigen mode calculation. From the results it was found that the external source neutroncould decrease the sensitivity to the fuel composition considerably and enhance the fuel loading flexibility of the subcritical reactor.

Shielding Analysis of Nuclear Data Measurement Facility Using EGS4 and MCNP4 Codes

The electron accelerator facility generating high-energy particle for nuclear data measurements has a probability of radiation emission at all times, and thus, the shielding analysis for the facility should be performed. In this work, two Monte Carlo codes, EGS4 and MCNP4B, were employed for the accurate calculations of radiation source term and ambient dose at the working areas. EGS4 code was used in the calculation of neutron and photon sources from the accelerator beam line and the beam target. The ambient dose at the working areas was calculated by MCNP4B code using neutron and photon source terms calculated from the EGS4 runs. The results showed that the ambient dose at the working areas was much higher than the design limit of Pohang Accelerator Laboratory, 5 μSv/hr, and thus, it is recommended that the additional effective shields, lead shield of 14 cm thick at the LINAC room and 11 cm thick at the target room, should to be installed for ensuring radiation safety of the nuclear data measurement facility.