• Nuclear Engineering and Technology
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• v.48 no.6
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• pp.1321-1329
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• 2016

To get an insight into the operating characteristics of the passive residual heat removal system of molten salt reactors, a two-phase natural circulation test facility was constructed. The system consists of a boiling loop absorbing the heat from the drain tank, a condensing loop consuming the heat, and a steam drum. A steady-state experiment was carried out, in which the thimble temperature ranged from $450^{\circ}C$ to $700^{\circ}C$ and the system pressure was controlled at levels below 150 kPa. When reaching a steady state, the system was operated under saturated conditions. Some important parameters, including heat power, system resistance, and water level in the steam drum and water tank were investigated. The experimental results showed that the natural circulation system is feasible in removing the decay heat, even though some fluctuations may occur in the operation. The uneven temperature distribution in the water tank may be inevitable because convection occurs on the outside of the condensing tube besides boiling with decreasing the decay power. The instabilities in the natural circulation loop are sensitive to heat flux and system resistance rather than the water level in the steam drum and water tank. RELAP5 code shows reasonable results compared with experimental data.

• Nuclear Engineering and Technology
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• v.52 no.5
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• pp.869-877
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• 2020

A 24-month Advanced Power Reactor 1400 (APR1400) core with a very-low-boron (VLB) concentration has been investigated for an inherently safe and high-performance PWR in this work. To develop a high-performance APR1400 which is able to do the passive frequency control operation, VLB feature is essential. In this paper, the centrally-shielded burnable absorber (CSBA) is utilized for an efficient VLB operation in the 24-month cycle APR1400 core. This innovative design of the VLB APR1400 core includes the optimization of burnable absorber and loading pattern as well as axial cutback for a 24-month cycle operation. In addition to CSBA, an Er-doped guide thimble is also introduced for partial management of the excess reactivity and local peaking factor. To improve the neutron economy of the core, two alternative radial reflectors are adopted in this study, which are SS-304 and ZrO₂. The core reactivity and power distributions for a 2-batch equilibrium cycle are analyzed and compared for each reflector design. Numerical results show that a VLB core can be successfully designed with 24-month cycle and the cycle length is improved significantly with the alternative reflectors. The neutronic analyses are performed using the Monte Carlo Serpent code and 3-D diffusion code COREDAX-2 with the ENDF/B-VII.1.

• The Korea Journal of Herbology
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• v.33 no.4
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• pp.27-33
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• 2018

Objectives : The roots of Dipsacus asper had been used as the herbal medicine "Cheon-Sokdan" in Korea. Moreover, the roots of Phlomoides umbrosa were used as "Han-Sokdan." In the present study, a comparative anatomical comparison of Cheon-Sokdan, Han-Sokdan, and Ilbon-Sokdan were conducted, because Ilbon-Sokdan, the roots of Dipsacus japonicus, was regarded as substitute of Cheon-Sokdan. Methods : For this study, permanent preparations were made using a paraffin embedding method. Anatomical features of these three Sokdans were observed using a light microscope. Results : The starch grains of parenchyma cells and the amounts of calcium oxalate crystals hardly differed among the three plants. Particularly, the longitudinally-sectioned vessels of the three plants showed a wide variety depending on the focal depth of the light microscope. Therefore, these features could not be considered as obligate criteria for distinguishing these plants. The shape of the xylem was linear in Cheon-Sokdan and Ilbon-Sokdan, whereas that in Han-Sokdan was wedge-shaped. The phloem of Cheon-Sokdan and Ilbon-Sokdan were rhomboid, whereas that of Han-Sokdan was thimble-like. Therefore, the shape of xylem and phloem appeared as good criteria for distinguishing Han-Sokdan from the other plants studied. Cheon-Sokdan and Ilbon-Sokdan showed characteristics similar in many parts. However, in the xylem of Ilbon-Sokdan, fiber bundles were more developed than those of Cheon-Sokdan. Therefore, the development of fiber bundles in xylem was considered suitable for distinguishing between Cheon-Sokdan and Ilbon-Sokdan. Conclusions : The identification-keys established in this study would be helpful for identifying microscopic features among the three Sokdans.