Radiation Physics and Engineering
Volume:6 Issue: 1, Winter 2025

Currently, passive safety systems are critical for enhancing nuclear reactor safety and dependability. To limit the chance of the core being uncovered in pool-type research reactors, a siphon pipe with a penetration in the pool wall higher than the core level can be used as the pool outlet pipe. Using a siphon breaker as a passive safety system is vital. The hydraulic study of the siphon breaker line passive safety system for a pool-type research reactor is carried out using the RELAP5 code. The hydraulic analysis and modeling are carried out on a 16-inch coolant outlet siphon pipe, taking into account 16-inch and 8-inch break diameters, as well as siphon breaker line diameters of 2, 2.5, 3, and 4 inches. As a consequence, the undershooting height for a 16-inch break and a 4-inch siphon breaker line is -36.7 cm. The undershooting height is -51.4 cm when using an 8-inch break and a 2-inch siphon breaker line. Compared with the findings to the reference experimental data, the largest difference is -3.1 cm and the smallest difference is -0.1 cm. The findings obtained indicate a substantial agreement between the simulated and experimental results.

Radiation shielding plays a crucial role in various industries, including nuclear and space exploration. Among the most abundant elements and isotopes found in nature, B-10 has one of the highest neutron absorption cross-sections, closely followed by Li-6. It is worth noting that hydrogen, with its light nucleus, serves as an excellent neutron reflector. Surprisingly, the potential of the lithium borohydride molecule (LiBH4), which consists exclusively of these elements, as a shield against neutron radiation has not yet been explored. This study investigates various materials that can potentially be used as shields. First, we assessed traditional shields and previous optimizations for shielding. The findings showed that concrete containing 10% B4C yielded the best results. High-performance concrete (HPC) replaced regular concrete. By gradually incorporating lithium borohydride into the shield, along with the appropriate level of boron carbide, further optimization was achieved. Calculations were performed using the MCNPX 2.7E code. The introduction of the new shield resulted in a significant 40% reduction in volume compared with the previous sample. The study findings showed that a 30 cm thick shield effectively blocked 95% of the total neutrons and 92% of the total gamma radiation. Additionally, it was noted that the shielding effects of lithium borohydride against fast neutrons are greater than those of boron carbide. Various parameters and data of the designed shield were calculated and compared with those of the previous sample.

During external beam radiation therapy, patients are exposed to secondary radiation sources, contributing to out-of-field doses with potential long-term adverse effects. Understanding photon and electron energy spectra is essential to evaluate the secondary effects of modern radiotherapy. This study aimed to evaluate the photon and electron fluence spectra and mean energy beyond the field edge as well as in-field regions for several small radiotherapy fields. The study used International Atomic Energy Agency (IAEA) phase-space files for the 6 MV photon beams produced by three commonly used linear accelerators to generate small and standard fields. The mean photon and electron energies were calculated at multiple depths and off-axis distances for the three linear accelerators and a predefined 6 MV spectrum. The study found that the photon fluence spectra strongly depend on spatial positions and vary significantly as a function of depth, off-axis distance, field size, and linac model. Furthermore, the behavior of electrons is depth-dependent beyond the field edge, where the mean electron energy near the surface is greater than in-field regions, especially in small fields, leading to surface dose enhancement.

Xylanase enzymes produced by Trichoderma afroharzianum have significant industrial applications, including animal feed, food, biofuel, and textile industries. Creating novel sources of Trichoderma strains using induced gamma irradiation mutation can increase enzyme production. According to this, Co-60 gamma irradiation has been used to develop a mutant strain of T.afroharzianum. T.afroharzianum mutants were isolated, and qualitative and quantitative screening were used to evaluate the production of the extracellular enzymes with wheat bran waste as a substrate. The best T.afroharzianum mutant strain was identified using the DNA barcoding method. The highest xylanase activities were observed in the superior mutant of T.afroharzianum NAS107-M82, which is approximately 3.3 times higher than its parent strain. The electrophoretic pattern of proteins showed that synergistically, the exo-glucanase I, endo-glucanase III, and the xylanase I enzymes hydrolyzed the wheat bran. This study collectively highlights the diverse potential of gamma-radiated T. afroharzianum mutant-derived xylanases in various industrial and agricultural applications, showcasing their importance in enzyme production.

Neutron scattering facilities are widely applied to study the properties of materials. A beam of monochomatic neutrons or a widespread wavelength band of neutrons is used to irradiate the sample which is going to be analyzed at the scattering laboratory. Shielding of incident neutrons also the scattered ones from the sample should be definitely done to decrease the laboratory dose rates. Also, mapping of the dose rate distributions helps to the laboratory users to avoid high neutron/gamma exposures. The present study uses a computational method to simulate neutron and gamma dose rates’ distributions inside TRR diffraction facility laboratory. Not only the simulation method helps to design the laboratory boundary or the laboratory walls so that behind its walls the personal exposures remain as low as possible, but also gives warnings to the facility users about the high dose regions around the beam exit when the facility is under operation. The carried-out work showed after the laboratory boundary, summation of the neutron and gamma dose rates are less than 3 μSv.h-1. In addition, the carried-out benchmark studies by using experimental data in this work confirms the simulations with less than 20% relative discrepancy.

The present study examined the vitrification of spent ion exchange (IEX) resins in a borosilicate glass matrix on the laboratory scale. For this purpose, the simulated spent IEX resin waste prepared by doping non-radioactive cobalt and cesium elements on a combination of cationic and anionic resins was employed. For glass wasteform preparation, heat-treated (at 150 °C) spent IEX resin was mixed with borosilicate glass ferrite in the range of 20-40 weight percent and then melted at 1200 °C. To evaluate the prepared glass wasteforms, their volume reduction ratio (VRR) and chemical stability were investigated. According to the obtained results, with the increase in the spent IEX resin loading, the volume reduction ratio of the final wasteform increases. However, in the samples with spent IEX resins loading higher than 30 wt.%, phase separation (white color containing insoluble sulfate) was observed on the surface of the glass. Investigations showed that glass wasteform containing 30 wt.% spent IEX resins provides the best conditions for waste immobilization. The relative volume reduction ratio of this sample was measured as 86.61%. The normalized leaching rate of cesium and cobalt from this wasteform was calculated as 7.43×10-5 and 6.93×10-5 g.m-2.day-1, respectively, using the PCT method.

Microwave coupling plays an important role to energize the electrons in an electron cyclotron resonance ion source (ECRIS) plasma. Several components are hired for wave transition from a magnetron to the ECR plasma chamber. In this work, DC break, pressure window, ridged waveguide and plasma chamber have been designed and simulated by COMSOL Multiphysics to transmit the microwave power. The power and frequency are 1 kW and 2.45 GHz, respectively. The results show the TE111 mode gets excited and 9.9 mm quartz pressure window maximize the forward transmission power to the cavity. The DC break is based on utilizing the insulating rings along the WR-284 waveguide, which has low wave return loss for a wide range of frequencies. A four-ridged waveguide is considered for impedance matching and electric field focusing. The amplification of the electric field in the middle of cylindrical plasma chamber is satisfied with dimensions of Ø9 cm×10 cm.

‎This work aimed to assess the secondary cancer risk for patients undergoing brain and pelvic radiotherapy with high-energy linear accelerators (LINAC)‎. ‎Photoneutrons are produced in the LINAC's head when operating above 7 MeV and are not considered in radiotherapy treatment planning‎. ‎The MCNPX2.6 Monte Carlo code was used for LINAC's head simulation‎. ‎The photon and neutron doses were calculated in tissues/organs of an International Commission on Radiological Protection (ICRP) male reference voxel phantom undergoing pelvic and brain radiotherapy‎. The results indicated that the neutron equivalent dose was higher for tissues/organs located close to skin and‎, ‎contrary to the photon equivalent dose‎, ‎did not decrease sharply for tissues/organs outside of the irradiation field‎. ‎Notably‎, ‎neutron equivalent dose distribution was almost homogenous in whole body and did not depend on the treatment type and location of target organ‎. ‎Therefore‎, ‎an undesirable dose was received by healthy tissues/organs‎, ‎leading to an increase in secondary cancer risk‎. ‎Based on the obtained results‎, ‎the neutron effective dose for the pelvic and brain treatment were 0.20 and 0.26 mSv.Gy-1‎, ‎respectively‎. ‎The results also indicated that maximum secondary cancer risk due to neutrons was for colon (0.026 %) in the pelvic treatment‎, ‎while in brain treatment‎, ‎it belongs to stomach (0.036 %) for a delivered dose of 70 Gy‎. ‎It is recommended that a mean neutron effective dose value of 0.23 mSv.Gy-1 can be considered in brain and pelvic treatment planning for evaluating the secondary cancer risk of high-energy LINAC radiotherapy‎.