Shielding Design Methods Research Articles

Experimental Verifications for a Multiobjective Shielding Design Method on a p-Be Neutron Source With Injection of 7 MeV Protons

Experimental Verifications for a Multiobjective Shielding Design Method on a p-Be Neutron Source With Injection of 7 MeV Protons

Characterization of the Radiation Contamination in an 18MV Linac Treatment Room Made of some Nanoparticles Mixture

Purpose: Shielding against radiation in radiotherapy and radiology requires deep knowledge of radiation physics and shielding design methods. The application of nanoparticles in the photon and neutron dose moderation has been proven in the literature.
 Materials and Methods: Effective neutron mass removal cross-section (ΣR/ρ) was for the ordinary concrete doped with 50nm in diameter nanosphers mixture of Fe2O3(5%), WO3(5%), B4H (5%), Pb2O3(5%) was estimated with MCNP5 Monte Carlo (MC) code and N-XCOM computational program. An 18MV linac room made of the nanoparticles dopped ordinarily simulated. Additionally, the room was considered with three legs in the maze and photoneutron and capture γ-ray Dose Equivalent (DE) were estimated at the modeled rooms maze.
 Results: Total ΣR/ρ with energies 100 keV-2000keV was estimated using MC and N-XCOM as 0.02802-0.02687 cm2/gand 0.02810- 0.02687 cm2/g, respectively. Total ΣR/ρ of the neutron for the pure ordinary concrete was estimated by MC code and N-XCOM with energies 100 keV-2000keV as 0.02802-0.02687 cm2/g and 0.02810- 0.02687 cm2/g. Borated Polyethylene (BPE) and Lead required thickness calculated as 7.43×10-06 mm and 4.73×10-06 mm for the capture γ-ray shielding.

Semi-empirical and semi-quantitative lightweight shielding design method

Semi-empirical and semi-quantitative lightweight shielding design method

Shielding Failure of High-Voltage Substations: A Fractal-Based Approach for Negative and Positive Lightning

A fractal-based approach is presented for the direct-stroke shielding analysis of high-voltage substations. The proposed method considers the effect of lightning polarity and the stochastic nature of the lightning attachment phenomenon. An application to a typical 69 kV substation reveals that shielding failures may occur even if the shielding design is realized with IEEE Std 998-2012 methods. This can be explained by the fact that the shielding design methods adopted by IEEE Std 998 do not consider the effects of lightning polarity and object height on striking distance. In addition, IEEE Std 998 methods adopt a deterministic approach on shielding failure analysis neglecting the branched and tortuous behavior of lightning discharges. Fractal-based simulation results show a considerable dispersion of striking distance and a significantly higher shielding failure probability for downward positive lightning than negative lightning. This work forms a discussion framework on shielding failure analysis following a stochastic approach; this approach may explain unexpected shielding failures, such as those reported in IEEE surveys, and can be used for the direct-stroke shielding design of mission-critical high-voltage substations.

Numerical simulations on active shielding methods comparison and wrapped angle optimization for gradient coil design in MRI with enhanced shielding effect.

The switching of a gradient coil current in magnetic resonance imaging will induce an eddy current in the surrounding conducting structures while the secondary magnetic field produced by the eddy current is harmful for the imaging. To minimize the eddy current effects, the stray field shielding in the gradient coil design is usually realized by minimizing the magnetic fields on the cryostat surface or the secondary magnetic fields over the imaging region. In this work, we explicitly compared these two active shielding design methods. Both the stray field and eddy current on the cryostat inner surface were quantitatively discussed by setting the stray field constraint with an ultra-low maximum intensity of 2 G and setting the secondary field constraint with an extreme small shielding ratio of 0.000 001. The investigation revealed that the secondary magnetic field control strategy can produce coils with a better performance. However, the former (minimizing the magnetic fields) is preferable when designing a gradient coil with an ultra-low eddy current that can also strictly control the stray field leakage at the edge of the cryostat inner surface. A wrapped-edge gradient coil design scheme was then optimized for a more effective control of the stray fields. The numerical simulation on the wrapped-edge coil design shows that the optimized wrapping angles for the x and z coils in terms of our coil dimensions are 40° and 90°, respectively.

Comparison of computed tomography shielding design methods using RadShield

Purpose. To comprehensively compare four computed tomography (CT) scanner shielding design methods using RadShield, a Java-based graphical user interface (GUI). Methods. RadShield, a floor plan based GUI, was extended to calculate air kerma and barrier thickness using accepted methods from the National Council on Radiation Protection and Measurements (NCRP), the British Institute of Radiology, and a method using isodose maps, for spatially distributed points beyond user defined barriers. For a stationary CT scanner, the overall shielding recommendations found using RadShield were also compared to those found by American Board of Radiology certified diagnostic medical physicists using the conventional NCRP dose length product method and the isodose map method. Results. The results between methods differed significantly for calculation point locations beyond the gantry and to the rear of the gantry. Overall shielding design recommendations across the four methods yielded similar average air kerma and thickness values for the barriers. Conclusions. RadShield was extended to perform CT shielding design and proved reliable using four methods.

Assessment of the integrity of structural shielding of four computed tomography facilities in the greater ACCRA region of Ghana

The structural shielding thicknesses of the walls of four computed tomography (CT) facilities in Ghana were re-evaluated to verify the shielding integrity using the new shielding design methods recommended by the National Council on Radiological Protection and Measurements (NCRP). The shielding thickness obtained ranged from 120 to 155 mm using default DLP values proposed by the European Commission and 110 to 168 mm using derived DLP values from the four CT manufacturers. These values are within the accepted standard concrete wall thickness ranging from 102 to 152 mm prescribed by the NCRP. The ultrasonic pulse testing of all walls indicated that these are of good quality and free of voids since pulse velocities estimated were within the range of 3.496±0.005 km s(-1). An average dose equivalent rate estimated for supervised areas is 3.4±0.27 µSv week(-1) and that for the controlled area is 18.0±0.15 µSv week(-1), which are within acceptable values.

Design of piezoelectric transducer layer with electromagnetic shielding and high connection reliability

Piezoelectric transducer (PZT) and Lamb wave based structural health monitoring (SHM) method have been widely studied for on-line SHM of high-performance structures. To monitor large-scale structures, a dense PZTs array is required. In order to improve the placement efficiency and reduce the wire burden of the PZTs array, the concept of the piezoelectric transducers layer (PSL) was proposed. The PSL consists of PZTs, a flexible interlayer with printed wires and signal input/output interface. For on-line SHM on real aircraft structures, there are two main issues on electromagnetic interference and connection reliability of the PSL. To address the issues, an electromagnetic shielding design method of the PSL to reduce spatial electromagnetic noise and crosstalk is proposed and a combined welding–cementation process based connection reliability design method is proposed to enhance the connection reliability between the PZTs and the flexible interlayer. Two experiments on electromagnetic interference suppression are performed to validate the shielding design of the PSL. The experimental results show that the amplitudes of the spatial electromagnetic noise and crosstalk output from the shielded PSL developed by this paper are − 15 dB and − 25 dB lower than those of the ordinary PSL, respectively. Other two experiments on temperature durability ( − 55 °C–80 °C ) and strength durability (160–1600με, one million load cycles) are applied to the PSL to validate the connection reliability. The low repeatability errors (less than 3% and less than 5%, respectively) indicate that the developed PSL is of high connection reliability and long fatigue life.

Radiation safety design for the J-PARC project

The High-Intensity Proton Accelerator Project, named J-PARC, is in progress, with the aim of enabling studies on the latest basic science and the advancement of nuclear technology. In the project, a high-energy proton accelerator complex with the world's highest instantaneous intensity is under construction. In order to establish a reasonable shielding design, both simplified and detailed design methods were used in the shielding design of J-PARC. This paper reviews the present status of the radiation safety design study for J-PARC.

Neutron shielding calculations in a proton therapy facility based on Monte Carlo simulations and analytical models: criterion for selecting the method of choice

Proton therapy facilities are shielded to limit the amount of secondary radiation to which patients, occupational workers and members of the general public are exposed. The most commonly applied shielding design methods for proton therapy facilities comprise semi-empirical and analytical methods to estimate the neutron dose equivalent. This study compares the results of these methods with a detailed simulation of a proton therapy facility by using the Monte Carlo technique. A comparison of neutron dose equivalent values predicted by the various methods reveals the superior accuracy of the Monte Carlo predictions in locations where the calculations converge. However, the reliability of the overall shielding design increases if simulation results, for which solutions have not converged, e.g. owing to too few particle histories, can be excluded, and deterministic models are being used at these locations. Criteria to accept or reject Monte Carlo calculations in such complex structures are not well understood. An optimum rejection criterion would allow all converging solutions of Monte Carlo simulation to be taken into account, and reject all solutions with uncertainties larger than the design safety margins. In this study, the optimum rejection criterion of 10% was found. The mean ratio was 26, 62% of all receptor locations showed a ratio between 0.9 and 10, and 92% were between 1 and 100.

Radiation Measurements and Shielding Calculations for Spent Fuel Casks

Radiation measurements were carried out on two kinds of newly developed NFT-type casks, the NFT-22B and the NFT-14P, in order to evaluate the cask shielding design safety margins and supply benchmarks for cask shielding calculation. The measurements involved placing about 100 sets of small dosimeters on and 1m away from the cask surface. The time integral dose equivalents for 2 to 3 weeks were measured. And gamma ray energy spectrums at some measurement points were also measured by a Nal scintillation counter. The measured dose equivalent rates were 1/2 -1/20 lower than the values estimated by the shielding design method which took the radiation source strength of the spent fuels loaded into the casks into consideration, confirming that the shielding design method used for the casks was conservative enough. The causes of the conservatism in the shielding design were also investigated. Furthermore the effects of changes in hydrogen and B4C concentrations in epoxy resin used for neutron shielding in the NFT casks were evaluated.

Shielding Design to Obtain Compact Marine Reactor

The marine reactors equipped in previously constructed nuclear ships are in need of the secondary shield which is installed outside the containment vessel. Most of the weight and volume of the reactor plants are occupied by this secondary shield. An advanced marine reactor called MRX (Marine Reactor X) has been designed to obtain a more compact and lightweight marine reactor with enhanced safety. The MRX is a new type of marine reactor which is an integral PWR (The steam generator is installed in the pressure vessel.) with adopting a water- filled containment vessel and a new shielding design method of no installation of the secondary shield. As a result, MRX is considerably lighter in weight and more compact in size as compared with the reactors equipped in previously constructed nuclear ships. For instance, the plant weight and volume of the containment vessel of MRX are about 50% and 70% of those of the Nuclear Ship MUTSU, in spite of the power of MRX is 2.8 times as large as the MUTSU's reactor. The shielding design calculation was made using the AN ISN, DOT3.5, QAD-CGGP2 and ORIGEN codes. The computational accuracy was confirmed by experimental analyses.

Shielding Design to Obtain Compact Marine Reactor.

The marine reactors equipped in previously constructed nuclear ships are in need of the secondary shield which is installed outside the containment vessel. Most of the weight and volume of the reactor plants are occupied by this secondary shield. An advanced marine reactor called MRX (Marine Reactor X) has been designed to obtain a more compact and lightweight marine reactor with enhanced safety. The MRX is a new type of marine reactor which is an integral PWR (The steam generator is installed in the pressure vessel.) with adopting a water- filled containment vessel and a new shielding design method of no installation of the secondary shield. As a result, MRX is considerably lighter in weight and more compact in size as compared with the reactors equipped in previously constructed nuclear ships. For instance, the plant weight and volume of the containment vessel of MRX are about 50% and 70% of those of the Nuclear Ship MUTSU, in spite of the power of MRX is 2.8 times as large as the MUTSU's reactor. The shielding design calculation was made using the AN ISN, DOT3.5, QAD-CGGP2 and ORIGEN codes. The computational accuracy was confirmed by experimental analyses.

A survey of industry practices regarding shielding of substations against direct lightning strokes

Results of a survey of industry practices regarding shielding of substations against direct lightning strokes are presented and analyzed. The survey is based on responses from 114 companies, including consultants and utilities both from within and from outside North America. The survey identifies the shielding design methods in use, the factors affecting the selection of a shielding method, the shielding design criteria and the governing factors, the performance of the different shielding methods and miscellaneous related aspects. The survey revealed a large number (35) of shielding failure incidents; 34 occurred in systems designed using either the fixed-shielding angle method or Wagner's 1942 method.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Calculations of a Fast-Neutron Shielding Experiment for Evaluating Approximate Shielding Design Methods

A fast-neutron shielding experiment performed by Atomics International is analyzed using modified ENDF/B-II data in Russian format, space-dependent elastic removal corrections, and one-dimensional discrete ordinates calculations. The scattering cross sections are transport corrected P0. The analysis of this particular experiment showed 1. The data used for sodium, iron, chromium, and nickel are reasonably good for predicting the space-dependent spectra and flux attenuation within the uncertainties of the approximate methods used.2. The void streaming correction of Olsen is quite accurate and necessary for this experiment, due to streaming at dosimetry gaps.3. The treatment of higher order anisotropy in the neutron scattering does not appear to be very important in this analysis.4. The need for a two-dimensional calculation to better predict flux attenuation, accounting for the spatial variation of the transverse flux distribution (buckling reduction with depth of penetration).