https://scholarworks.unist.ac.kr/handle/201301/68 2026-04-08T21:40:07Z https://scholarworks.unist.ac.kr/handle/201301/91248 Title: Electrorefining of HANA-4 Cladding Scrap in LiCl-KCl Salts for Volumetric Decontamination of Irradiated Cladding Containing Nb-94 Author(s): Son, Sungjune; Hur, Jungho; Park, Jaeyeong; Kim, Pyeong-Hwa; Hwang, Il Soon Abstract: Nb-94, an activation product in irradiated cladding, is a major concern in geological disposal. As the Nb-94 is distributed throughout the cladding, volumetric decontamination should be applied to separate between Zr and Nb. In this study, the radiological characteristics of irradiated HANA-4 cladding were investigated using the ORIGEN-ARP code to derive a decontamination factor for Nb-94, 11. The electrochemical behavior of Nb was evaluated by cyclic voltammetry using low NbCl5 concentrations (0.15 and 0.5 wt. %) in LiCl-KCl at 773 K. Nb has a complex redox behavior but it was found the nobler tendency could be utilized for Zr electrorefining. Two electrorefining tests were performed by applying constant potentials of -0.85 V and -1.2 V (vs. Ag/AgCl 1 wt. %) at the anode and cathode, respectively. From the anodic test, Zr metal was obtained at the bottom of the salt, by two-step reactions among Zr4+ ,Zr2+, and Zr. Meanwhile, ZrCl and Zr were co-recovered as deposits in the cathodic test. The results revealed good separation performance between Zr and Nb. The Nb concentrations were 2.1 and 20.3 ppm in the product from the anodic and cathodic test, respectively, supporting feasibility of satisfying the radioactivity concentration limits of Gyeongju Disposal Facility. 2026-06-30T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/91172 Title: Development of GPU-Accelerated CMFD for STREAM3D-GPU Neutron Transport Code Author(s): Setiawan, Fathurrahman; Dzianisau, Siarhei; Lee, Deokjung Abstract: This study presents the implementation of the graphics processing unit (GPU)-based coarse mesh finite difference (CMFD) acceleration in STREAM3D-GPU using the directive-based OpenACC framework. The offloading process follows a structured approach of assessment, parallelization, and optimization, with data structures reorganized to maximize GPU efficiency. Performance evaluations on three-dimensional OPR-1000 reactor models demonstrate up to a 22-fold reduction in CMFD run time compared to the CPU version, with the greatest improvements observed in the linear system solver and flux convergence routines due to extensive parallelization and concurrent execution. Numerical verification using depletion simulations of the BEAVRS benchmark confirmed that the GPU implementation maintained high fidelity, with eigenvalue deviations within 5 pcm and maximum differences in power distribution below 0.6%. 2026-02-28T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/90780 Title: Explicit and simplified modeling of in-core instrument for emitter region reaction rate calculation using STREAM/RAST-K Author(s): Kim, Kyeongwon; Yun, Dongmin; Kim, Wonkyeong; Kwon, Sung Ju; Fathurrahman, Setiawan; Lee, Deokjung Abstract: This study proposes an efficient and accurate method to model the In-Core Instrumentation (ICI) that utilizes Self-Powered Neutron Detectors (SPNDs) for real-time monitoring of neutron flux and power distribution in reactor cores. Traditional core analyses have often neglected the detailed ICI effects, leading to potential inaccuracies in reactivity and power predictions. The newly developed ICI models, based on simplified geometry, explicitly consider the resonance self-shielding effects on the emitter nuclide cross sections, irradiation behavior during burnup, and reactivity perturbations. The use of a two-term rational approximation significantly improves the accuracy of absorption cross sections of emitter materials compared with reference data. The reactivity effect of ICI is approximately 276 pcm for a typical Westinghouse-type fuel assembly, causing critical rod position shifts of 2-6 cm in full-core simulations. In boron-free SMR conditions, absorption reaction rates of emitters were evaluated using critical rod search calculations. Results indicate that pseudo modeling shows deviations up to 20% in end-of-cycle power predictions, whereas explicit and simplified ICI approaches consistently match with actual assembly power. Therefore, these improved ICI modeling techniques are essential for precise instrumentation and reactivity evaluation in advanced boron-free SMR cores. 2026-05-31T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/90522 Title: Development of Fe–Cr–Si deposited layer manufactured by laser directed energy deposition process Author(s): Kim, Gidong; Nam, Hyunbin; Hwang, Taewoo; Kim, Seunghyun; Kim, Ji Hyun; Song, Sangwoo Abstract: In this study, the mechanical and corrosion characteristics of a corrosion-resistant layer made of stainless steel (STS) 316 L and Fe–Cr–Si alloy powder were investigated using laser-directed energy deposition (DED). In the STS 316 L deposited specimen, both the substrate and deposited layer were face-centred cubic (FCC). The deposited Fe–Cr–Si layer was clearly separated from the substrate because it was composed of body-centred cubic (BCC). Despite the phase differences, the surface of the Fe–Cr–Si-deposited layer showed a lower corrosion rate than that of the STS 316 L. All the deposited specimens exhibited typical high-temperature tensile behavior. However, the Fe–Cr–Si deposited layer at 600 °C showed a notable reduction in strength and increased elongation compared to the room temperature (RT) and 300 °C test results owing to the carbide concentration and phase transformation in the deposited layer. Because nuclear facilities mainly operate at temperatures below 600 °C, Fe–Cr–Si materials can also be used as nuclear piping coating materials. This study provides a mechanism for the high-temperature properties and corrosion resistance of the Fe–Cr–Si deposited layer and makes it competitive for application in fourth generation nuclear power systems. © 2023 The Authors 2024-01-31T15:00:00Z