Volume 90, Issue 4

The use of cationic surfactant CTAB (cetyltrimethylammonium bromide) to modify bentonite has the advantages of convenience, speed, and large loading capacity. Due to the chemical similarity between rhenium and technetium, many hydrogeological studies on technetium use rhenium as a substitute for cold testing. Therefore, in this study, CTAB was used as a modifier for organic modification of bentonite by cation exchange method to change its properties and better adsorb Re(VII). The feasibility of using CTAB-modified bentonite as an additive in backfill materials was discussed through a series of experiments. The research results indicate that the addition of modified bentonite significantly inhibits the diffusion of Re(VII) in bentonite, manifested as a decrease in total diffusion amount, diffusion flux, apparent diffusion coefficient, and effective diffusion coefficient, while increasing the rock capacity factor. When the mass ratio of modified bentonite in the diffusion medium increases from 0 % to 20 %, the effective diffusion coefficient of Re decreases from 19.56 × 10−11 cm 2 /s to 0.046 × 10−11 cm 2 /s, the rock capacity factor of the diffusion medium increases from 0.995 to 29.43. In addition, the increase in pH value and ionic strength affects the surface sites of bentonite, thereby increasing the surface diffusion coefficient and effective diffusion coefficient of rhenium, while the rock bearing capacity decreases. These findings suggest that the adsorption capacity of TcO 4 − can be enhanced by doping modified bentonite in backfill materials, reducing the migration of TcO 4 − within the backfill material, potentially providing benefits for the safe storage of high-level radioactive waste.

Small reactors have the advantages of compact structure and wide application scenarios, and can be deployed in remote areas. However, due to the complex structure and special application scenarios, it is more difficult for operators to diagnose and identify accident information. This article conducts accident diagnosis research using simulated data from IRIS reactors. An accident diagnosis model based on LSTM neural network has been established. The diagnostic ability of the model has been analyzed when there is an error in the time of the accident occurrence. When there are numerical and time errors in the dataset, the simulated diagnostic accuracy is 96.8 %. The method of using a diagnostic model based on shutdown signal partitioning has improved the diagnostic ability of transient operating events and minor accident conditions, achieving an accuracy of 96.1 % when there is ±5 % noise in the dataset. By optimizing the output form of the diagnostic model, the diagnosis of unknown accidents was achieved. When using LOCA and LOFA accidents as unknown accidents, the diagnostic accuracy of the model reached 98.5 %.

Limiter is one of the key components in any tokamak with the critical design consideration including removal of thermal load while withstanding embrittlement and erosion resulting from high neutron flux incidence. The Pakistan Spherical Tokamak (PST) limiter is a material-based limiter having graphite as armor material attached to passively cooled copper heatsink. The maximum temperature of plasma facing surface reaches 434.355 K while that of copper block reaches 325.069 K using graphite as plasma facing material, thus the limiter is capable of effectively removing 1 MW/m 2 heat flux while limiting the maximum temperature of constituent materials below recrystallization temperature. In this paper, the thermal integrity and performance of PST limiter is accessed. Suitable PFM is selected based on limiter transient thermal performance, global maximum temperature, and copper block temperature rise. The methodology adopted is validated by comparison analytical solution. Graphite is determined to be suitable PFM for upgraded PST divertor mainly because of lower coolant surface temperature.

The aim of this study is to investigate the effect of temperature variation on the performance of the NaI (Tl) detectors, specially focusing on the shifting in photo-peak position and its count per second (CPS). The experiment was conducted using a 137 Cs source with activity of 7 µCi under controlled ambient temperature with six target temperatures ranging from −10 to +40 °C while the detector is equipped with a temperature stabilizer and its temperature was set to the constant temperature of 40 °C. For each target temperature, detector counts were recorded five times under two applied detector voltages, namely HV700 and 750 V. Spectra were analyzed using a code developed in MATLAB. The practical method introduced here could be used for future calibrations of the NaI (Tl) Gamma detectors used in density gauges working in outdoor environments.