This study presents the design and simulation of an energy degrader system for the Thailand Institute of Nuclear Technology (TINT) cyclotron facility, developed to reduce 15-30 MeV proton beams to 2-5 MeV for PIXE and PIGE applications. SRIM and Geant4 simulations were utilized to optimize foil thickness and characterize beam dynamics. Varying the foil thickness (0.1 -1.4 mm) achieved degraded energies between 2 and 15 MeV. However, multiple Coulomb scattering increased the energy spread (1-29%) and RMS transverse emittance 80-395 mm & centerdot;mrad). Four representative cases yielded energies of 11.8, 9.1, 6.3, and 2.8 MeV, with energy spread peaking at 16.9% for the lowest energy. To mitigate beam quality degradation, a two-stage collimator system was implemented. This reduced the transverse emittance by approximately 5 mm & centerdot;mrad compared to a single-collimator setup, achieving proton transmission rates of 0.3-2% (0.6-4 & micro;A from a 200 & micro;A initial beam). Radiation safety was evaluated by mapping the neutron ambient dose equivalent, H*(10), using Geant4. Peak neutron dose exceeding 1.5 & times; 10-12 & micro;Sv per primary proton near the degrader assembly, confirming that local shielding with borated polyethylene is essential. These results provide benchmark beam parameters for future PIXE and PIGE applications and support the design of downstream beam transport systems, including a dipole magnet spectrometer for energy selection and analysis.
Boiling and drying accident is thought to have the largest potential radiological consequence. If the cooling time of reprocessing fuel is short, volatile Ru (106Ru) gives a significant impact. Previous experiments on Ru volatilization were conducted by externally heating 100 similar to 400 mL simulated waste. Under such conditions, a large temperature difference occurs inside the waste once it begins to dry. Therefore, it is difficult to correlate the obtained waste temperature vs. time curve with that during an accident. In the present experiment, the Ru volatilization curves were obtained when 4.6, 2.0, and 0.91 mL of simulated waste were heated at constant rates of 0.07, 0.2, and 0.8 degrees C min-1, respectively. Under these conditions, the waste temperature was the same as the external heating temperature. In previous experiments, only one or two volatilization peaks were observed, but this time four peaks were observed. Until now, Ru volatilization was thought to occur through the oxidation of Ru nitrosyl nitrate in concentrated nitric acid and after acid evaporation its thermal decomposition. However, the appearance of four peaks cannot be explained by this mechanism and may be due to complex changes in the chemical form of Ru compound with increasing temperature. The experimental results can serve as basic data for predicting Ru volatilization during an accident. Using the Arrhenius-type equations for Ru volatilization derived from these basic data and the waste temperature change during the accident derived in our previous report, we attempted to predict the Ru volatilization curve over the accident progression time.
Accurate perception of three-dimensional radiation environments is essential for nuclear accident response and nuclear facility decommissioning. This paper presents a mobile robot-based method for 3D radiation field reconstruction. Unlike conventional interpolation approaches, the proposed approach establishes a physics-guided framework in which source localization supports radiation field mapping. An autonomous patrol-to-source-seeking switching strategy is first designed using a mechanical collimator. Angle-constrained particle filtering and maximum likelihood estimation are then employed to rapidly identify source parameters. These estimates provide accurate physical priors for subsequent field reconstruction. A physics-informed heteroscedastic Gaussian process model, termed PI-HGPR, is further introduced for radiation field inference. The model captures fluctuations in high-radiation regions by incorporating heteroscedastic noise. It also incorporates a physics-based attenuation kernel to reduce oversmoothing under sparse sampling. Finally, the reconstructed continuous radiation field is fused with a 3D geometric map to generate a radiation point cloud. Experimental results demonstrate that the proposed method maintains high reconstruction accuracy under sparse-sample conditions, achieving an RMSE below 7%, and provides a reliable data foundation for unmanned nuclear emergency exploration.
In this study, the effects of beta-ray radiation on the optical and dielectric properties of InSe thin film were investigated using a Sr-90 beta-source at doses of 0, 5, 10, and 20 kGy. To analyze the optical properties of the film, the transmittance (T) and absorbance (A) measurements were performed using a UV-Vis spectrophotometer in the 500-1000 nm spectral range. Optical and dielectric parameters including absorption coefficient, extinction coefficient, optical band-gap, refractive index, dielectric constant and optical conductivity were obtained from T and A data. As the radiation dose increased, transmittance increased while absorbance decreased. Under beta-irradiation, these dose-dependent changes confirm the occurrence of defect formation, band rupture, and local atomic rearrangements. The band-gap energy (Eg) InSe film, which has the direct optical transition, was determined from Tauc plot. The Eg values were found in the range of 1.67 eV (0 kGy) to 1.59 eV (20 kGy), that is, they were decreased with increasing radiation dose. These results demonstrate that the optical response of the InSe film is strongly dependent on both wavelength and irradiation dose.
In the present study, we conducted criticality analysis using a model that incorporates material changes occurring in disposal environments. The goal was to evaluate post-closure criticality of engineered barrier system for direct disposal of spent nuclear fuels with reasonable conservatism of material changes, avoiding excessive margins. The analyzed material changes included corrosion of fuel cladding, IT/GT tube (an Instrumentation Tube and a control rod Guide Tube), canister, and the resulting evolution of buffer materials. The reactivity was evaluated for those individual material changes and maximum reactivity was also evaluated considering the combination of their effects. The results show that the effective multiplication factor keff remained below the upper subcritical limit of 0.95 and was lower than the keff calculated by the previous conservative model. This result suggests that introducing realistic material changes, including those that potentially cause higher reactivity in geological environments, reduces the predicted likelihood of criticality when compared against the purely conservative model.
In order to facilitate the treatment of deformed geometries for the multiphysics simulation in reactor physics, the Smoothed Particle Hydrodynamics (SPH) method is applied to the Simplified P-3 (SP3) neutron transport calculation. To accurately perform the SP3 neutron transport calculation, the SPH method with second-order accuracy for second derivatives, denoted as SPH(2), is utilized to reduce discretization errors, especially those arising from irregular particle arrangements. Furthermore, the space-dependent kinetics calculation is implemented using Proper Orthogonal Decomposition (POD) with an on-the-fly procedure. The developed code was verified in a two-dimensional xy geometry through the ramp transient case of the TWIGL benchmark problem, by comparing the numerical results with reference values obtained by MOC with the Multigrid Amplitude Function (MAF) method. Consequently, this study demonstrated that the numerical results of k(eff) using SP3-SPH(2) agreed well with the reference MOC calculation, even for irregular particle arrangements. Thanks to the application of SPH(2), average biases and standard deviations in the numerical results of both criticality and kinetics calculations were successfully reduced as the particle size decreased, which could not be achieved using the conventional SPH method.
The effect of temperature on hydrogen generated from radiolysis was investigated to determine the safety implications in nuclear fuel reprocessing, particularly in cases involving loss of cooling for high-level radioactive solutions. Radiolytic hydrogen production poses a risk due to its flammability, especially when it accumulates in confined spaces without ventilation. Herein, generation of radiolytic hydrogen from an actual nuclear fuel-derived solution is investigated. Compared to previous studies using a plutonium nitric acid solution, this study evaluates radiolytic hydrogen yield under more realistic conditions, reflecting post-irradiation fuel composition. G-values of H-2 are determined at multiple temperatures, and the impact of alpha, beta, and gamma radiation doses is evaluated using PHITS-based simulations. Findings from this study confirmed a reduction in hydrogen yield due to scavenging effects of high-concentration nitric acid and metal ions dissolved in the solution, and temperature dependence appeared to be minor. A weak decreasing trend of G-values with temperature under agitated conditions might be related to hydrogen consumption by palladium species.
The use of ultrasonic sensors has been proposed as a method for understanding the status of decommissioning work at the Fukushima Daiichi Nuclear Power Station (FDNPS). Piezoelectric materials for ultrasonic transducers are known to have high radiation-resistance. Therefore, radiation-resistance related electronic modules such as pulsers and preamplifiers for ultrasonic sensors are also required. Since high radiation fields exist inside the PCV (Primary Containment Vessel) and RPV (Reactor Pressure Vessel), it is difficult to use electronic equipment incorporating conventional semiconductor integrated circuits. In this study, high-radiation-resistant pulser and preamplifier for ultrasonic sensors were fabricated, and their performance tests were performed in a 60Co gamma-ray irradiation facility. The electronic circuits of the pulser and the preamplifier consisted of SiC-JFETs, ceramic capacitors, and resistors to improve the radiation-resistance. The electronic characteristics of SiC-JFET were investigated. The IDS-VGS characteristics of the SiC-JFET did not change significantly up to an absorbed dose of 10 MGy (in water). The ultrasonic sensor unit for distance measurement with 1.7 MHz ultrasonic waves was normally operated at a dose rate of approximately 1.8 kGy/h (in water).
