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Radiation safety assessment of a worker for the treatment facilities of the mixed spent resin from heavy water reactor

Sat, 31 Jan 2026 15:00:00 GMT

Title: Radiation safety assessment of a worker for the treatment facilities of the mixed spent resin from heavy water reactor Author(s): Yoon, Ja Yeong Abstract: The treatment facility for mixed spent resin at Wolsong CANDU nuclear power plant involves potential radiation exposure risks to workers during operation. This study established realistic normal and accident scenarios in advance to ensure long term and stable operation of the treatment facility to be installed, and provided the number of operations, time, and methods for conducting a radiation safety assessment. The primary components of the treatment facility include 1 kW and 9 kW scale beta-nuclide removal unit. This research evaluated shielding safety of the beta-nuclide removal units, analyzed worker doses during waste transport before and after treatment and examined exposure during injection, assessed doses under the leakage scenario of radioactive airborne particulates and maintenance operations. The study established realistic operational scenarios through empirical experiments and quantitatively analyzed both external and internal dose rates of workers. Using the VISIPLAN 4.0 code, the external dose rates of radionuclides contained in the mixed spent resin were evaluated, and internal dose rates were calculated considering the facility volume, breathing rate, and working time. For the shielding safety evaluation, lead and water shields of varying thickness were applied, and increasing shielding thickness consistently reduced spatial dose rates. The before treatment scenario assumed normal operation without leakage, while the after treatment scenario evaluated worker doses by accounting for the production of 5 kg of spent resin and 0.5 kg of combined zeolite and activated carbon. The injection scenario involved lifting the reactor lid and loading 2 kg of mixed spent resin into the facility. The leakage scenario of radioactive airborne particulates, the analysis considered a 20 % generation of radioactive airborne particulates relative to the unit volume for both the 1 kW and 9 kW scale beta-nuclide removal unit. And the maintenance scenario simulated pipe replacement based on an actual blockage incident. Therefore, this study conservatively assessed radiation safety by presenting work methods based on an annual dose of 20 mSv. Mixed spent resin treatment facility is currently in the pre-installation stage, during which various feasibility and performance verifications are being conducted. Accordingly, presenting measures to maintain radiological protection for workers during future operation will provide essential baseline data for securing the long-term safe operation of the facility. Major: Department of Nuclear Engineering

Carbon-14 degassing from surface waters: Experimental validation and numerical simulations using the film model

Sat, 31 Jan 2026 15:00:00 GMT

Title: Carbon-14 degassing from surface waters: Experimental validation and numerical simulations using the film model Author(s): Oh, Youjin Abstract: This study aims to establish a comprehensive understanding of ¹⁴C degassing behavior in surface waters and to improve the accuracy of radiological safety assessments for disposal scenarios involving ¹⁴C-bearing waste. Although the RESRAD-ONSITE code is widely used for evaluating residual radioactivity and dose assessment, its current modeling framework neglects the degassing of ¹⁴C from surface water, resulting in conservatively high predictions of ¹⁴C concentration in surface water and subsequent ingestion doses. To address this limitation, a combined experimental and numerical framework was developed in this study. Laboratory-scale experiments were performed to quantify the rate of ¹⁴C degassing under various pH, temperature, and solution-depth conditions. The experiments revealed that ¹⁴C degassing is strongly governed by chemical speciation and boundary-layer diffusion, with lower pH and shallower water depth leading to faster degassing. The results were benchmarked against a COMSOL Multiphysics-based stagnant film model that considers both molecular diffusion and chemical equilibrium reactions within the aqueous boundary layer. The model reproduced the experimental trends with good agreement, validating its ability to simulate the dominant mechanisms controlling ¹⁴C transfer from water to air. Using the validated model, a series of simulations were conducted to quantify the degassing constant (k) across a wide range of environmental conditions, including pH (7-9), temperature (15-25 °C), water depth (1-20 m), and boundary-layer thickness derived from wind speed (3-10 m/s). The resulting dataset was fitted using an ordinary least squares (OLS) regression to develop a predictive equation for k, effectively capturing the nonlinear and interaction effects among variables such as pH–temperature. The regression model demonstrated high accuracy (R² > 0.99) and low error (RMSE < 0.05), confirming its suitability for practical applications. To evaluate its applicability, the regression-derived k values were integrated into the RESRAD-ONSITE code as a post-processing correction to account for time-dependent ¹⁴C degassing from surface water. Incorporating degassing resulted in a substantial reduction in both predicted ¹⁴C concentration in surface water and fish ingestion doses, thereby suggesting a more realistic and less conservative assessment of ¹⁴C exposure pathways. This study is expected to serve as a useful basis for improving the understanding of ¹⁴C transport and degassing behavior in surface waters and for supporting more reliable safety assessments of ¹⁴C waste disposal. Major: Department of Nuclear Engineering

Improving Montmorillonite Dissolution Predictions for High-Level Waste Repositories through Model Validation and Experimental Condition Analysis

Sat, 31 Jan 2026 15:00:00 GMT

Title: Improving Montmorillonite Dissolution Predictions for High-Level Waste Repositories through Model Validation and Experimental Condition Analysis Author(s): Park, Chohyun Abstract: Montmorillonite, the primary mineral in bentonite buffer materials for deep geological disposal of high-level radioactive waste (HLW), is responsible for maintaining low permeability and providing radionuclide retardation capability. However, geochemical perturbations such as alkaline porewater conditions induced by cementitious materials may accelerate montmorillonite dissolution, potentially degrading buffer performance. Therefore, a reliable prediction of montmorillonite dissolution under repository-relevant conditions is essential for long-term safety assessment. In this study, the ability of the PFLOTRAN geochemical simulator to quantitatively predict montmorillonite dissolution behavior was evaluated based on the Transition State Theory (TST) kinetic framework. Preliminary modeling confirmed that pH-dependent dissolution trends, particularly the dominance of aluminum secondary species formation under high-pH conditions, could be qualitatively reproduced. Benchmarking against experimental datasets demonstrated that the model accurately predicts dissolution rates across various chemical conditions; however, discrepancies remained under high-temperature and high-pH conditions. To address this, the activation energy parameter for alkaline dissolution (Ea OH) was refined from 61 kJ/mol to 31 kJ/mol, resulting in improved agreement with experimental observations. Experimental variability was further examined by analyzing dissolution regimes. The results indicated that discrepancies observed at neutral pH were not caused by transport limitations but by high solution saturation maintained during experiments. The saturation state, quantified using Gibbs free energy changes, was shown to be sensitive to hydrodynamic conditions. A packed-column flow-through model was developed to investigate the effects of flowrate, reactive surface area, and reactor volume, demonstrating that reduced saturation can be achieved through proper experimental configuration. This work establishes a modeling strategy for improving the predictive reliability of montmorillonite dissolution under chemically perturbed repository conditions. The outcomes provide guidance for kinetic parameter evaluation and experimental design, contributing to reduced uncertainty in bentonite buffer performance assessments for deep geological disposal of HLW. Major: Department of Nuclear Engineering

Experimental Emulation of Neutron Induced Degradation in Stainless Steel without Ionizing Radiation

Thu, 31 Jul 2025 15:00:00 GMT

Title: Experimental Emulation of Neutron Induced Degradation in Stainless Steel without Ionizing Radiation Author(s): Ryoo, Hyeonje Major: Department of Nuclear Engineering