Shielding Requirements Research Articles

Photoneutron production mechanisms, their characteristics, and shielding strategies in high-energy linac environment: A review

Radiotherapy, a mainstay cancer treatment for patients worldwide, utilizes medical linear accelerators (linacs) with photon energies ranging from 4 MV to 25 MV. However, concerns arise at higher energies (>6 MV, particularly >10 MV). These high-energy photons interact with high-atomic number materials in the linac head and collimation system, generating unwanted neutrons through (γ,n) reactions. This neutron contamination, present in both photon and electron beams, is a significant issue. Neutrons, with their high Linear Energy Transfer (LET), are more effective at causing clustered DNA damage (single and double-strand breaks). These neutrons not only impact shielding requirements in treatment rooms but also increase out-of-field radiation doses for patients receiving high-energy photon therapy. Therefore, for radiotherapy treatments exceeding 6 MV, additional precautions become crucial, including enhanced door shielding and optimized treatment planning. This review discusses in detail the multifaceted aspects of neutron production and shielding requirements during radiotherapy.

An Optimal Radiation Shield Design of a Small Modular Nuclear Power Reactor by Genetic Algorithm

One of the critical concerns in developing small modular nuclear reactors (SMRs) is employing efficient radiation shielding consistent with the design and implementation requirements. Besides observing the radiation shielding requirements, the design process entails developing compact, lightweight shielding as well as ensuring the safety of the staff and radiation-sensitive equipment around the reactor under different operating conditions. Conventional methods of radiation shielding design are based on experiments conducted. Therefore, the resultant design involves trial and error, rarely achieving an optimal, effective, and efficient design. In this study, a multi-objective method based on the genetic algorithm coupled with the MNCP calculation code has been used to enhance the radiation shielding system of a SMR. Using this method, the thickness of different shielding layers has been optimized to minimize the total dose (neutrons and gamma) at the output, the weight, and the overall volume of the shielding. To assess and compare the method used to an implemented conventional method, a sample design of the MRX nuclear power reactor is considered. Using the optimization technique, the radiation shielding of the reactor has been redesigned and compared with the original design. This paper discusses the existing deficiencies in the initial design of the primary shield of the reactor as a design implemented based on conventional methods. Similar to the original design, the main materials considered for radiation shielding in consecutive layers were water and steel, and the final layer contained lead. The thickness of the different layers and their arrangements have been optimized to assess the upgraded method. The calculations indicate that the overall thickness of the proposed shielding is suggested as 93.8 cm compared to 140 cm to obtain the total dose of neutrons and gammas, which is suggested as less than 10 µSv/h. The results imply a 38.56% reduction in volume and a 17.24% reduction in weight of the radiation shielding compared to the reference reactor design.

Compact fusion blanket using plasma facing liquid Li-LiH walls and Pb pebbles

Liquid plasma facing walls allow for increased neutron-wall loading expanding the design space of fusion power-plants and experimental devices towards compact high-field reactors. This study presents the design of a compact radial build blanket for fusion devices composed of variable quantities of Lead (Pb) and Lithium-Lithium Hydride (Li-LiH). A tank-like cylindrical neutronic model of the early design of the stellarator reactor proposed by Renaissance Fusion is implemented in OpenMC (neutron transport and dose rate analyses). The reactor's radial build composition and blanket layer thicknesses are varied to fulfill the requirements on tritium breeding ratio (TBR), nuclear heat extraction, radiation shielding (for the coils, internal structures and external environment) for a stellarator-based power-plant. The analyses suggest that a radial build lower than a meter thick between the plasma and coils would be sufficient to allow for a TBR ∼ 1.60, an energy multiplication factor of ∼ 1.07, to capture ≥ 90% of the nuclear heat, limit the neutron fluence at the coils below 1019 n/cm2, and limit the structural damage on the liquid metal vessel and magnet structure. In particular, a blanket composed of 32 cm of Pb and Li-LiH, 54 cm of a heavy metal hydride such as vanadium hydride (VH2), along with a 1.3 m of concrete bioshield, would minimize the radial build of the stellarator reactor while fulfilling tritium breeding, shielding and heat extraction requirements.

Theoretical Analysis of a Magnetic Shielding System Combining Active and Passive Modes.

Considering the magnetic shielding requirements of both geomagnetic field and 50 Hz power-line frequency in the complex working conditions of the power grid, an electromagnetic shielding system combining active and passive modes is proposed in this article. A three-dimensional Helmholtz coil with a magnetic shielding barrel nested inside is established by the COMSOL simulation tool, and the magnetic shielding efficiency of the system is analyzed. Comparing different materials, the simulation results indicate that permalloy alloy exhibits better shielding performance than pure iron and nickel materials. Additionally, the overall shielding efficiency of the shielding barrel increases linearly with the number of multiple layers. Under the combined active and passive electromagnetic shielding conditions, the system achieves a shielding efficiency of SE = 113.98 dB, demonstrating excellent performance in shielding both AC and DC interference magnetic fields. This study provides theoretical guidance for the construction of magnetic shielding systems in electromagnetic interference environment.

Application of two-dimensional temperature response functions for reconstruction of divertor heat flux profile in commercial fusion reactors.

To keep the tritium breeding rate TBR > 1 and to meet the high heat load and neutron shielding requirements for the first wall and divertor in fusion demonstration (DEMO) reactors, the number of port plugs and other openings must be limited. To accomplish this, it is necessary to develop alternatives to the use of infrared (IR) thermography to determine the peak heat flux and the heat flux profile onto divertor targets. A divertor tile equipped with multiple temperature monitoring channels can be used to reproduce the temperature profile. To avoid the high temperatures and high neutron flux environment in a DEMO, the monitoring positions can be set well away from the irradiated surface. However, the spatial resolution of this method is lower than that provided by IR thermography. In the present work, we apply two-dimensional temperature response functions and the corresponding heat conduction model to temperature data obtained from a divertor tile surface in the large helical device to study the effects of the spatial resolution of the monitored temperature profile on the reconstructed heat flux profile. The findings provide information that will be useful in defining a method for embedding thermocouples into the divertor tiles of future DEMO reactors.

Electrical and Magnetic Properties of Materials for Electromagnetic Interference

General aspects about electromagnetic interference (EMI) have shown that various electronic and electrical devices, in the field of communications are very sensitive to many sources (emissions) of external electromagnetic waves with various bands of frequency components. All electrical equipment using radio communication contains intentional emitters and sensitive receivers. Since electrical and magnetic materials have different properties, the objective of this paper is to explore the shielding effectiveness of some materials and to suggest new compounds that satisfies the effective shielding requirements.

Large-Scale Fabrication of Tunable Sandwich-Structured Silver Nanowires and Aramid Nanofiber Films for Exceptional Electromagnetic Interference (EMI) Shielding.

The recent advancements in communication technology have facilitated the widespread deployment of electronic communication equipment globally, resulting in the pervasive presence of electromagnetic pollution. Consequently, there is an urgent necessity to develop a thin, lightweight, efficient, and durable electromagnetic interference (EMI) shielding material capable of withstanding severe environmental conditions. In this paper, we propose an innovative and scalable method for preparing EMI shielding films with a tunable sandwich structure. The film possesses a nylon mesh (NM) backbone, with AgNWs serving as the shielding coating and aramid nanofibers (ANFs) acting as the cladding layer. The prepared film was thin and flexible, with a thickness of only 0.13 mm. AgNWs can easily form a conductive network structure, and when the minimum addition amount was 0.2 mg/cm2, the EMI SE value reached 28.7 dB, effectively shielding 99.884% of electromagnetic waves and thereby meeting the commercial shielding requirement of 20 dB. With an increase in dosage up to 1.0 mg/cm2, the EMI SE value further improved to reach 50.6 dB. The NAAANF film demonstrated remarkable robustness in the face of complex usage environments as a result of the outstanding thermal, acid, and alkali resistance properties of aramid fibers. Such a thin, efficient, and environmentally resistant EMI shielding film provided new ideas for the broad EMI shielding market.

Study on Shielding Effectiveness of High Transmittance Coating Film Glasses against Electromagnetic Pulse

This study investigated the shielding effectiveness (SE) of glass materials with conductive coatings by establishing a 3000 × 3000 × 3000 mm electromagnetic pulse (EMP)—shielded room according to the EMP shielding requirements in the US military standard MIL-STD-188-125-1. The EMP SE of conductive-coated glass samples was measured and verified with the broadband EMP conditions of 10 kHz∼1 GHz. The conductive thin film coating on the glass was made by mixing conductive materials, including In2O3, SnO2, Ta2O5, NbO, SiO2, TiO2, and Al2O3, at different ratios. The mixed solutions were then coated onto the glass targets to facilitate conductive continuity between the conductive oxides and the shielding metal structure. The glass samples had dimensions of 1000 × 600 mm, which had electrolytic conductivity σ = 4.0064 × 103∼4.7438 × 103 (S/cm), 74∼77% transmittance, and 6.4∼6.8 Ω/□ film resistance. The experimental results indicated that the glass had SE of 35∼40 dB under 1 GHz EMP, satisfying the US National Coordinating Center for Communications’ Level 3 shielding protection requirement of at least 30 dB. The glass attenuated energy density by more than 1000 times, which is equivalent to shielding over 97% of EMP energy. Accordingly, the glass materials can be used as high-transmittance conductive glass for windows of automobiles, vessels, and aircrafts to protect from EMPs.

Simulation of radiation environment and design of multilayer radiation shield for orbital exploration of Jupiter

The harsh radiation environment of Jupiter imposes significant constraints on the shield design of spacecraft. Due to these constraints, traditional aluminum shields cannot meet the radiation shielding requirements needed for the exploration of Jupiter. In this paper, the design for a highly efficient radiation shield structure is proposed that utilizes a combination of high-Z/low-Z elements. A typical exploration orbit of Jupiter is selected, and the energetic particle radiation environment is calculated using the D&G83 model. The Geant4 toolkit is used to evaluate the shielding performance of materials, and quantitative simulations are performed to analyze the shielding efficiency of bilayer and trilayer shield structures under an areal density constraint of 4.5 g/cm2. Based on the simulations, an optimal shield structure is determined. The simulation results show that the integral electron flux with energy greater than 3 MeV is approximately three orders of magnitude greater than that of geostationary orbit with an orbit of 4000 km at the perijove and 5420000 km at the apojove, resulting in an enormous total dose effect. The optimal shield structure is a bilayer structure that comprises of a tantalum outer layer with a density of 3.5 g/cm2 and a polyethylene inner layer with a density of 1.0 g/cm2. This shield has the ability to reduce the total radiation dose to 1559 Gy per year, which is 32 % lower than that of traditional aluminum shields. Findings in this research are critical for design of radiation shields, and can be used for performing reliability analyses and predicting the lifespan of spacecraft during the development process.

Preliminary CFD and EM analysis of the ECRH equatorial launcher port plug prototype towards the CFETR

The CFETR is the next generation magnetic confinement tokamak, its increasing heating needs and stringent shielding requirements present new challenges for the ECRH launcher. In an effort to evaluate the viability of the equatorial launcher, a port plug prototype is designed and its performance under steady state or some interrupted events is assessed. The well-configured steel/water ratio is beneficial to improve its shielding capability and effectively mitigate the 493 kW heat. The maximum temperature of the port plug is less than 300 °C when the inlet temperature is 70 °C, and the average outlet water temperature reaches 142 °C. The worst EM case is a major disruption of the plasma, which would induce about 200 kN force on the port plug at the end of the plasma current linear decay. The combined heat and EM force loads on the port plug would result in a total deformation of 1.7 mm and a maximum equivalent stress of 320 MPa, with little impacts on the port plug or the surrounding vacuum vessel. As the installation of the port plug, the H and He generation rates of the surrounding vacuum vessel have increased by about 2 % and 1 % separately, but remain lower than the limit of 1 appm/FPY, and the nuclear heat density of the toroidal field coils has increased by about 5%.

The study of shielding design parameter (thickness) in two health tertiary institutions in Katsina Metropolis, Nigeria

The safety of the patient is of highest importance during diagnostic imaging which uses various forms of ionizing radiations mainly photons (x-rays and gamma rays). Both the patient and personnel working in the diagnostic facility may be exposed to unintentional source of radiations during diagnostic imaging. This study was conducted at the Federal Medical Center, Katsina and General Amadi Rimi Specialist Hospital, Katsina to assess the shielding adequacy of the barriers required to attenuate the intensity of X-ray to recommended limit. The National Council on Radiation Protection and measurement (NCRP), Report No 147 was used to evaluate the shielding barriers of the radiographic rooms in the two facilities. Calculation was done using the number of patients (N), occupancy factor (T), Design dose limit (P) and the distance to the occupied area (controlled and uncontrolled area). The result shows that the room area meets the recommendation of Nigeria Nuclear Regulatory Agency (NNRA) of at least 16 m2 and the shielding requirement for the primary barrier is slightly higher than secondary barrier of each room. The calculated shielding requirement for the primary barrier of room I, room II and room III of Federal Medical Center, Katsina and room IV of General Amadi Rimi Specialist Hospital, Katsina are 0.59 mm, 0.46 mm, 0.36 mm and 0.48 mm respectively. The maximum calculated shielding requirement for the secondary barriers in room I, room II, and room III of Federal Medical Center, Katsina and room IV of General Amadi Rimi Specialist Hospital, Katsina are 0.55 mm, 0.48 mm, 0.63 mm and 0.48 mm respectively. The ratio of the calculated to current material thickness is less than one (<1) for all the rooms.This indicates that the shielding barriers in the facilities are adequate. Hence, can accommodate future increase in the number of patients examined in the diagnostic rooms per week.

PEDOT:PSS and AgNW synergistically contributed high electromagnetic shielding performance for polyurethane-based composite coating

To meet the electromagnetic shielding requirements of complex shaped products, we prepared an environmentally friendly, efficient electromagnetic shielding coating on polyethylene terephthalate (PET) using water-based polyurethane, silver nanowire (AgNW), and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS). The addition of PEDOT:PSS not only notably improved the dispersion of AgNWs in the matrix and also acted as bridges between AgNWs, so the coating’s conductivity was greatly enhanced at a low AgNW content. The conductivity and EMI shielding effectiveness (EMI SE) of the coating with only 24.8 μm thickness and 30 wt% AgNWs reached 19,225 S/m and 68.8 dB, respectively. The EMI SE at such a thin thickness and low AgNW content is outstanding compared with previously reported literature. The coating also shows sufficient flexibility and adhesion stability, and mechanical robustness under sonication and chemical environments. Also, the coating can be attached to a variety of representative substrates, such as polypropylene, nylon, PET, glass, wood and metal.

(Invited) Effect of Gaseous Tritium Environments on Betavoltaic Device Longevity

Direct betavoltaic energy conversion is a specialized energy harvesting technology, converting beta radiation from a radiation source directly into electricity using a semiconductor. Of the most common beta emitting isotopes, tritium betavoltaics hold promise owing to the high specific activity of solid tritium compounds, low shielding requirements and relatively high availability. Betavoltaic devices offer great promise to produce continuous quantities of nanowatt to microwatt power over the course of several years, particularly for low-power sensor, medical, and space applications where sunlight is too sparse for solar cell use or where battery replacement is challenging.Canadian Nuclear Laboratories (CNL) is currently developing betavoltaic devices based on tritium. CNL has unique facilities to produce, fabricate and test betavoltaic devices. Computational techniques have been used to address challenges of longevity and electron-hole pair generation in semiconductor materials, in particular (In,Ga)P. Long-term studies on test wafers in different tritium-containing environments and the effects on power output and longevity will also be discussed.

Microwave processed metal nanoparticles/MoO3-PVA photoactive nano-composites for energy applications

MoO3-PVA films hybridized with silver and copper nano-particles mediated by microwave heating were studied for energy applications. The composites films were characterized by Infra-red (FTIR), Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), UV–Visible spectroscopy and X-ray diffraction (XRD). The crystallite size from XRD peak width was estimated to be about 60–65 nm in the nanocomposite. The electromagnetic interference (EMI) shielding efficiency of so generated composites showed that metal containing composites have higher efficiency in X-band. The EMI study showed promising scope for application in low shielding requirement areas. The so-generated silver containing hybrid system resulted in visible light tunable band-gap (2.34–2.81 eV). Ag-MoO3-PVA (Sample PV-C) showed more than 90 % photocatalytic degradation of methylene blue dye.

Nuclear scoping analysis of ITER bioshield top lid toward its preliminary design review

During ITER operations, electronics located in the crane hall, which is above the tokamak, will be exposed to neutron and photon fields from both the plasma and the activated water. To protect the electronics, the implementation of dedicated shielding on the crane hall platform and the bioshield top lid is required. The design demands optimisation attending to constructability, weight limits, and radiation shielding requirements. This work evaluates eight shielding configurations by assessment of the neutron flux and dose accumulated over 4700 h of operation at 500 MW for electronics protection. This corresponds to a neutron wall load of 0.3 MW a/m² as specified in the ITER Project Specification. An intermediate-source approach has been followed with SRC-UNED, considering all relevant radiation sources while minimising the computational time required. Results were presented at the top lid Conceptual Design Review aiming to support decision-making. Further optimisation has since been performed to reach a top lid proposal for its Preliminary Design Review. All outcomes show that radiation levels above the north and south crane hall platforms are compatible with the critical electronics requirements.

Radiation protection studies for the INRNE-BAS cyclotron facility using Monte Carlo FLUKA code

The Bulgarian National Cyclotron Centre at the Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences (INRNE-BAS), is going to be a new facility dedicated to production of medical radioisotopes and research in the corresponding fields. This work details the shielding requirements of the facility and the preliminary radiological studies that we have carried out. The activity concentration of the long-lived radioisotopes is also evaluated which provides a useful guideline for the decommissioning plan of the facility. For these purposes we have performed simulations with the Monte Carlo particle transport and interaction code FLUKA.

Study on Performance of New Flexible Shielding Materials and First Demonstration Application in Chinese Pressurized Water Reactor Nuclear Power Plant

Abstract Excessive gamma rays will be emitted when a nuclear power plant is under overhaul, leading to a certain number of hotspots. To meet the shielding requirements of these hotspots, a new type of flexible shielding material with a “sandwich structure” has been developed. The new flexible shielding materials consist of two parts: one is silicone rubber with excellent physical and chemical properties by adding reasonable multicomponent additives as a matrix, and the other is lead powder as a shielding body. This kind of material, with lead powder dispersed uniformly in silicone rubber, was prepared through a mixing process. Based on this, the article has carried on the discussion with the performance of the functional layer of the new flexible shielding materials. The problem of the process stability of ultrafine powder distributed uniformly in a matrix with various densities among different regions has been solved as well. Furthermore, this kind of material has been adopted at the Chinese pressurized water reactor nuclear power plant as the first demonstration project. The site shielding effect has been recognized by the World Association of Nuclear Operators. As a result of this research, it is possible that the design of a radiation shield for a short or long time can be made quickly when a nuclear power plant is running or being overhauled. Meanwhile, this study is of great significance for the popularization and application of shielding materials.

Study on the effect of neutron shielding design on tritium breeding based on water-cooled ceramic blanket for CFETR

The Chinese Fusion Engineering Test Reactor (CFETR) is a magnetic confinement fusion reactor independently designed and developed by China, which is based on the ITER design experience. As one of the candidates for the CFETR, the water cooled ceramic blanket (WCCB) mainly carries out many important tasks, such as tritium breeding and radiation shielding. The high tritium breeding ability is one of the most significant goals of the blanket. For the design of the CFETR, in addition to meeting the requirements of tritium breeding, the design of the blanket must also consider meeting relevant shielding limits. Due to the limited space of the blanket, the improvement in tritium breeding space will inevitably lead to the reduction in neutron shielding space behind the breeding area, and vice versa. Therefore, under the premise of meeting the requirements of neutron shielding, increasing the tritium breeding space as much as possible is the focus of research. In this work, a three-dimensional neutronics model containing the WCCB blanket is developed, and the neutronics performance is calculated based on 1.5 GW fusion power. A set of nuclear analyses are carried out by the MCNP code, including analysis of the neutron wall load, tritium breeding ratio (TBR), and fast neutron fluence of the TF coil. It is found that the shielding space of certain blanket modules could be optimized. After the shielding optimization, the global TBR increased from 1.168 to 1.186, an increase of 0.018 TBR. The current research has important guiding significance for the future design and optimization of the WCCB for the CFETR.

Space neutron radiation shielding property of continuous fiber and functional filler reinforced polymer composite using Monte Carlo simulation

For radiation shielding and lightweight requirements, fiber-reinforced polymer (FRP) composite has advantages in serving as a structure-shielding multifunctional material due to low-Z element nature and excellent mechanical properties. This study established the Monte Carlo simulation model of continuous fiber and filler reinforced epoxy composite to research neutron radiation shielding, which contains the microstructure of the composite. For validation, the numerical results of the proposed model were compared with the experimental results and found in good agreement. Then, the effects of fiber and filler distribution were studied. The neutron linear and mass attenuation coefficients of various composites were simulated to evaluate the shielding performance and lightweight effect. It shows that the boron compound is critical for shielding thermal neutrons, and the shielding effectiveness for fast neutrons mainly depends on the type of fiber. The structural design and stacking sequence of fibers and fillers significantly affect neutron shielding performance. Compared with Al-alloy, obvious low-weight advantage is obtained for shielding neutrons. The shielding mechanism and energy deposition inside composites were also analyzed.

Heavy concrete shielding properties for carbon therapy

As medical facilities are usually built at urban areas, special concrete aggregates and evaluation methods are needed to optimize the design of concrete walls by balancing density, thickness, material composition, cost, and other factors. Carbon treatment rooms require a high radiation shielding requirement, as the neutron yield from carbon therapy is much higher than the neutron yield of protons. In this case study, the maximum carbon energy is 430 MeV/u and the maximum current is 0.27 nA from a hybrid particle therapy system. Hospital or facility construction should consider this requirement to design a special heavy concrete. In this work, magnetite is adopted as the major aggregate. Density is determined mainly by the major aggregate content of magnetite, and a heavy concrete test block was constructed for structural tests. The compressive strength is 35.7 MPa. The density ranges from 3.65 g/cm3 to 4.14 g/cm3, and the iron mass content ranges from 53.78% to 60.38% from the 12 cored sample measurements. It was found that there is a linear relationship between density and iron content, and mixing impurities should be the major reason leading to the nonuniform element and density distribution. The effect of this nonuniformity on radiation shielding properties for a carbon treatment room is investigated by three groups of Monte Carlo simulations. Higher density dominates to reduce shielding thickness. However, a higher content of high-Z elements will weaken the shielding strength, especially at a lower dose rate threshold and vice versa. The weakened side effect of a high iron content on the shielding property is obvious at 2.5 μSv/h. Therefore, we should not blindly pursue high Z content in engineering. If the thickness is constrained to 2 m, then the density can be reduced to 3.3 g/cm3, which will save cost by reducing the magnetite composition with 50.44% iron content. If a higher density of 3.9 g/cm3 with 57.65% iron content is selected for construction, then the thickness of the wall can be reduced to 174.2 cm, which will save space for equipment installation.