[en] Single-crystal TiN(111) layers, 45 nm thick, were grown on MgO(111) by ultrahigh vacuum reactive magnetron sputter deposition in pure N₂ discharges at T_s=700 degree C. Epitaxial Al(111) overlayers, 160 nm thick, were then deposited at T_s=100 degree C in Ar without breaking vacuum. Interfacial reactions and changes in bilayer microstructure due to annealing at 620 and 650 degree C were investigated using x-ray diffraction and transmission electron microscopy (TEM). The interfacial regions of samples annealed at 620 degree C consist of continuous ≅7-nm-thick epitaxial wurtzite-structure AlN(0001) layers containing a high density of stacking faults, with ≅22 nm thick tetragonal Al₃Ti(112) overlayers. Surprisingly, samples annealed at the higher temperature are more stable against Al₃Ti formation. TEM analyses of bilayers annealed at 650 degree C (10 degree C below the Al melting point) reveal only the self-limited growth of an ≅3-nm-thick interfacial layer of perfect smooth epitaxial wurtzite-structure AlN(0001) which serves as an extremely effective deterrent for preventing further interlayer reactions. [copyright] 2001 American Institute of Physics

[en] The escape rate and the fraction of fission products released to the reactor coolant, which are required for the determination of radioactive source terms for normal operating conditons and for the analysis of radiological consequences for accident conditions, respectively, were preliminary evaluated for Zr-U metallic fuel

[en] Zr-U metallic fuel that is composed of Zr-1Nb clad and fuel meat - a binary alloy of Zr and U - is being developed in KAERI. Since dimensional changes in fuel is required as a function of burnup for fuel design and performance analysis, based on measured data for irradiated metallic fuel rods whose characteristics are similar to those of KAERI's, models for change in fuel meat volume, fuel meat cross-sectional area and fuel length have been developed

[en] A code for evaluating the temperature of Zr-U metallic rod has been developed. Finite element (FE) method is adopted for the developed code sharing the user subroutines which has been prepared for the ABAQUS commercial FE code. The developed program for the Zr-U metallic fuel rod corresponds to a nonlinear transient heat transfer problem, and uses a sparse matrix solver for FE equations during iterations at every time step. The verifications of the developed program were conducted using the ABAQUS code. Steady state and transient problems were analyzed for 1/8 rod model due to the symmetry of the fuel rod and full model. From the evaluation of temperature for the 1/8 rod model at steady state, maximal error of 0.18 % was present relative to the ABAQUS result. Analysis for the transient problem using the fuel rod model resulted in the same as the variation of centerline temperature from the ABAQUS code during a hypothetical power transient. The distribution of heat flux for the entire cross section and surface was almost identical for the two codes

[en] The following 4 research items have been studied to establish a CANDU safety analysis system and to develop the relevant elementary technology for CANDU reactors. First, to improve and validate the CANDU design and operational safety analysis codes, the CANDU physics cell code WIMS-CANDU was improved, and validated, and an analysis of the moderator subcooling and pressure tube integrity has been performed for the large break LOCAs without ECCS. Also a CATHENA model and a CFD model for a post-blowdown fuel channel analysis have been developed and validated against two high temperature thermal-chemical experiments, CS28-1 and 2. Second, to improve the integrated operating system of the CANDU safety analysis codes, an extension has been made to them to include the core and fuel accident analyses, and a web-based CANDU database, CANTHIS version 2.0 was completed. Third, to assess the applicability of the ACR-7 safety analysis methodology to CANDU-6 the ACR-7 safety analysis methods were reviewed and the safety analysis methods of ACR-7 applicable to CANDU-6 were recommended. Last, to supplement and improve the existing CANDU safety analysis procedures, detailed analysis procedures have been prepared for individual accident scenarios. The results of this study can be used to resolve the CANDU safety issues, to improve the current design and operational safety analysis codes, and to technically support the Wolsong site to resolve their problems

[en] Root uptake and underground migration of Mn-54, Co-60, Sr-85 and Cs-137 deposited during growing seasons of Korean staple crops such as rice, soybean, potato, Chinese cabbage, radish, red pepper and cucumber were investigated through radio-tracer experiments in greenhouse. H-3 experiments for rice and Chinese cabbage and iodine experiment for Chinese cabbage were also carried out. The effect of KCl and lime application on root uptake and migration of Mn-54, Co-60, Sr-85 and Cs-137 were studied. Long-term (2∼5 years depending on crops) behaviors of these radionuclides in soil-plant system were also investigated. Cs-137 concentrations in farm-land soils and crop plants collected in 33 regions of Korea were measured. Soil-to-plant transfer factors of Cs-137 in outdoor fields were compared with those from greenhouse experiments. An improved method of calculating root-uptake concentration of the radionuclide in crop plant was introduced to KFOOD, a food-chain computer code for normal operation. The direction of improving ECOREA, a food-chain computer code for accidental release, was discussed through comparing model calculation of Sr-90 and Cs-137 root-uptake concentrations with present experimental results. Annual food consumption rates and crop yields were updated. (author). 87 refs., 68 tabs., 58 figs

[en] Dense fully-002-textured polycrystalline TiN layers, 110 nm thick with a N/Ti ratio of 1.02±0.03, were grown on SiO₂ by ultrahigh vacuum magnetically unbalanced magnetron sputter deposition at T_s=450 deg. C in pure N₂ utilizing high N₂⁺/Ti flux ratios and low energy (E_N2⁺=20 eV) ion irradiation of the growing film. Al overlayers, 160 nm thick and possessing a strong 002 texture inherited from the underlying TiN, were then deposited at T_s=100 deg. C without breaking vacuum. Synchrotron x-ray diffraction was used to follow interfacial reaction paths and kinetics during postdeposition annealing as a function of time (t_a=200-1200 s) and temperature (T_a=500-580 deg. C). Changes in bilayer microstructure and microchemistry were investigated using transmission electron microscopy (TEM) and scanning TEM to obtain compositional maps of cross-sectional and plan-view specimens by energy dispersive x-ray analysis. The initial bilayer reaction step during annealing involves the formation of a continuous AlN interfacial layer which, due to local epitaxy with the TiN underlayer, grows with the metastable zinc-blende structure up to a thickness x≅3-5 nm, and with the wurtzite structure thereafter. Ti atoms released during AlN formation diffuse into the Al layer leading to supersaturation followed by the nucleation of dispersed regions of tetragonal Al₃Ti with inherited 002 preferred orientation. The aluminide domains grow rapidly until they reach the free surface; thereafter growth is two dimensional as Al₃Ti grains spread radially. The overall activation energy for Al₃Ti formation and growth is 1.8±0.1 eV. In situ synchrotron x-ray diffraction analyses during thermal ramping show that the onset temperature for interfacial reactions was increased by more than 100 deg. C for fully dense completely 002-textured bilayers compared to 111-textured bilayers deposited by conventional reactive sputter deposition

[en] Growth of TiN layers in most diffusion-barrier applications is limited to deposition temperatures T_s < or approx. 500 deg. C. We have grown polycrystalline TiN layers, 160 nm thick with a N/Ti ratio of 1.02±0.03 and a 111 texture, at T_s=450 deg. C on SiO₂ by ultrahigh vacuum reactive magnetron sputter deposition in pure N₂. Al overlayers, 160 nm thick with inherited 111 preferred orientation, were then deposited at T_s=100 deg. C without breaking vacuum. The as-deposited TiN layer is underdense due to the low deposition temperature (T_s/T_m≅0.23 in which T_m is the melting point) resulting in kinetically limited adatom mobilities leading to atomic shadowing which, in turn, results in a columnar microstructure with both inter- and intracolumnar voids. The Al overlayer is fully dense. Synchrotron x-ray diffraction was used to follow interfacial reaction kinetics during postdeposition annealing of the 111-textured Al/TiN bilayers as a function of time (t_a=12-1200 s) and temperature (T_a=440-550 deg. C). Changes in bilayer microstructure and microchemistry were investigated using transmission electron microscopy (TEM) and scanning TEM to obtain compositional maps of plan-view and cross-sectional specimens. Interfacial reaction during annealing is initiated at the Al/TiN interface. Al diffuses rapidly into TiN voids during anneals at temperatures ∼<480 deg. C. In contrast, anneals at higher temperatures lead to the formation of a continuous nanocrystalline AlN layer which blocks Al penetration into TiN. At all annealing temperatures, Ti atoms released during AlN formation react with Al to form tetragonal Al₃Ti at the interface. Al₃Ti exhibits a relatively planar growth front extending toward the Al free surface. Analyses of time-dependent x-ray diffraction peak intensities during isothermal annealing as a function of temperature show that Al₃Ti growth kinetics are, for the entire temperature range investigated, diffusion limited with an activation energy of 1.5±0.2 eV