http://hdl.handle.net/10203/19 KAIST Dept. of Nuclear and Quantum Engineering Sat, 07 Mar 2026 05:57:35 GMT 2026-03-07T05:57:35Z https://koasas.kaist.ac.kr:443/retrieve/65508/원자력및양자공학과.JPG http://hdl.handle.net/10203/19 http://hdl.handle.net/10203/338960 Title: Systematic investigation on neutronics and thermal-hydraulics model for multi-physics analysis of micro molten salt fast reactor with moderating reflector Authors: Park, Wooseong; Jeong, Yong Hoon Abstract: A moderating reflector in Molten Salt Fast Reactors (MSFRs) enables dual-spectrum core-combining advantages of both fast and thermal spectra-but introduces strong local power peaking and a positive reflector temperature coefficient (RTC), whose impacts in steady and transient states remain largely unexplored. To address the research gap, we systematically evaluated neutronics and thermal-hydraulics model effects on the multi-physics behavior of an MSFR with moderating reflector, using GeN-Foam and OpenMC. First, multi-group diffusion analysis with various multi-group cross section (MGXS) models was conducted, demonstrating that refined MGXS (30-group structure with multi-region spatial homogenization) model can provide reasonably accurate predictions for MSFR with moderating reflector. Next, the influences of different neutronics (N) and thermal-hydraulics (TH) models on steady-state multi-physics calculations were examined. The results show that explicit reflector region modeling in TH simulation, together with the refined MGXS model, is crucial for accurate multi-physics simulation. Finally, transient analysis of accident scenarios was performed to investigate the basic dynamic behavior of the system and to assess the impacts of the positive RTC and MGXS model. The results show that simple MGXS model exhibits delayed power response to negative temperature feedback, and that positive RTC effects are not significant over short-term periods. Fri, 01 May 2026 00:00:00 GMT http://hdl.handle.net/10203/338960 2026-05-01T00:00:00Z http://hdl.handle.net/10203/339053 Title: Small modular reactors (SMRs): Comparison of saturated versus superheated steam Rankine cycle under equal thermodynamic constraints Authors: Kim, Gyudong; Chae, YongJae; Chun, TakHyun; Lee, Jeong-Ik Abstract: With part-load operation is increasingly becoming important issue for small modular reactors (SMRs), two secondary Rankine cycles for a 500 MWth pressurized-water-reactor small modular reactor were compared under identical thermodynamic constraints: a saturated-steam cycle with a U-tube steam generator and a superheated-steam cycle with a once-through steam generator were designed under identical primary-side conditions and the same steam-generator pinch-point temperature difference. Moreover, feedwater heaters satisfied fixed terminal temperature difference and drain-cooler approach limits. Part-load performance (25-100 %) was evaluated using the Stodola-based off-design turbine model with wet-steam penalties and steam-generator pressure/temperature programs consistent with each generator type (i.e., constant-average-temperature for the U-tube steam generator; constant-secondary-pressure for the once-through steam generator). High-pressure turbine pressure ratio and the split between reheater bypass and third feedwater-heater extraction were optimized for maximizing net efficiency. Equipment sizing was assessed via total heat-transfer coefficient-area product. Both cycles achieved similar peak net efficiency. The superheated-steam cycle required lower steam mass flow and smaller total heat-transfer coefficient-area product (i.e., UA), indicating a compact power-conversion system. The saturated-steam cycle was slightly superior at full load, whereas the superheated-steam cycle maintained higher efficiency and smaller reheater and extraction-flow variations at part load. These results provide a constraint-matched benchmark for small modular reactor power conversion systems prioritizing compactness and part-load robustness. Fri, 01 May 2026 00:00:00 GMT http://hdl.handle.net/10203/339053 2026-05-01T00:00:00Z http://hdl.handle.net/10203/339175 Title: Steric stabilization and dissolution behavior of calcium silicate hydrate (C-S-H) colloids induced by polycarboxylate-based superplasticizer: An extended DLVO theory approach Authors: Eun, Hyeonjin; Kim, Hyeong-Jin; Kim, Hee-Kyung; Yun, Jong-Il Fri, 01 May 2026 00:00:00 GMT http://hdl.handle.net/10203/339175 2026-05-01T00:00:00Z http://hdl.handle.net/10203/337953 Title: Estimation of self-absorption correction factors for gamma-ray spectrometry of radioactive waste using MCNP Authors: Kim, Kyungmin; Jung, Kyunghun; Jang, Won-Hyuk; Choi, Yu-Jeong; Nam, Jong Soo; Kim, Tack-Jin; Cho, Gyuseong Abstract: Gamma-ray spectrometry is a suitable technique for the radiological characterization of radioactive waste. However, differences in material and density between certified reference materials (CRMs) serve as standards for calibration. The waste sample can cause self-absorption effects, necessitating appropriate corrections. This study presents a practical method for deriving self-absorption correction factors using MCNP6.2. A detailed detector model and measurement setup were constructed in MCNP6.2 and optimized by comparing simulation results with experimental measurements. Three different CRM geometries were employed to improve modeling accuracy. Simulations were refined across three HPGe detectors within 59.54-1836.05 keV energy range to achieve average and maximum deviation between simulated and measured FEPE (full energy peak efficiency) of 1.9 +/- 2.16 % and 4.9 +/- 1.9 %, respectively. Using the optimized MCNP inputs, self-absorption correction factors were calculated with densities ranging from 0.1 to 8.0 g/cm3. Additionally, the corresponding equations for effective path lengths were determined for specific geometries. The self-absorption effects were further evaluated for combustible, incombustible, and metallic waste over the same density range. The correction factors were derived and compared by material type. The validity of the proposed method was experimentally confirmed using concrete-based CRM. The results will improve accuracy and efficiency in sampling and activity concentration analysis in radioactive waste management. Wed, 01 Apr 2026 00:00:00 GMT http://hdl.handle.net/10203/337953 2026-04-01T00:00:00Z