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[en] Highlights: • Thorough analysis on all the cases in C5G7-TD benchmark. • Parametric study on the time step size. • Comprehensive comparison with other codes’ results. - Abstract: Verification and Validation (V&V) serves an important role in assessing the numerical methods implemented in a neutron transport code. However, very few benchmarks are available for verifying and validating the transient capability of neutron transport codes. In this paper, the transient methodology of the Transient Multilevel (TML) Method used in the MPACT code was verified using Phase I of the recently developed OECD/NEA C5G7-TD benchmark, which was specifically designed for validating the transport space-time simulations. The results in MPACT agree well with results of other codes. While this is not code validation, the results contributes to the MPACT verification base and provide an additional solution for the C5G7-TD benchmark which can increase the importance of the OECD benchmark to assess the performance of other transient neutron transport codes.
[en] In this work, radiation dosages and hazards emerging due to doses received by drivers and workers involved in transporting naturally occurring radioactive materials (NORM) in Egypt are assessed and compared with the accepted doses in many countries. Two cases were studied; the first case is of a truck driver and the other one was of the loading-unloading workers. The workers’ case was studied to estimate the doses and hazards to workers in the field of recycling materials. The annual working hours for truck drivers were defined, according to normal, heavy and abnormal duties, as 200, 400 and 600 hours. Working hours for loading-unloading workers were also selected under various conditions of duties to be 50, 100 and 150 annual hours. External and internal exposure for drivers and workers were estimated according to the properties of materials. Zircon, phosphate and bauxite were the assumed cargos. The doses due to inhalation of contaminated dust were considered in addition to the external dose of γ-radiation
[en] WMG, Inc. led a team of industry experts in the first of its kind packaging, transportation and disposal of four (4) Steam Generator Lower Assemblies (SGLAs). The project had a number of significant challenges including qualifying the SGLAs as IP-2 packages, implementing roadway improvements and orchestrating the use of three different modes of transportation. In the end, these SGLAs would be the first large components disposed at the WCS Disposal facility in Andrews Texas. The client was re-purposing the SGLA storage mausoleum for 'Fukushima equipment' preparedness so it became necessary to dispose of the assemblies. The WMG team needed to: - Dismantle the mausoleum to allow removal of the SGLAs, - Design, fabricate, deliver and install IP-2 SGLA packaging, and - Transport the packaged SGLAs from the client to the WCS facility for disposal. After qualifying the packaging as IP-2 containers, the SGLAs were loaded onto special equipment for over-the-road transport to the harbor in Kewaunee, WI. Following trans-load, the SGLAs were barged down Lake Michigan through the Mississippi River to the Port of Houston for another trans-load. The SGLAs arrived by rail at WCS' Andrews TX facility. Each transport segment required coordination for transport clearances, proper marking, labeling and placarding for that particular mode of transport as well as coordination with the team involved in moving the large packages from one conveyance to another. The project was completed with zero safety issues, significantly below dose goals, ahead of schedule, and within budget. (authors)
[en] Highlights: • Conventional Monte Carlo α-k iteration methods are improved in this paper. • A direct physical relation to adjust the α-eigenvalue is also derived. • Besides variance reduction, the need for a proper initial α is alleviated. • The proposed automatic shifting method highly improves the convergence rate. • A comparative analysis on the performance of α-adjusting techniques is presented. - Abstract: The α-k iteration method is a common approach for calculating the fundamental α- or time-eigenvalue. The bottleneck of the method lies in how to estimate or adjust the amount of α value in each iteration. Prolonged convergence as well as the need for a proper initial guess for the α-eigenvalue are two main deficiencies of commonly employed α adjusting techniques. This article proposes a direct physical relation to adjust the α-eigenvalue in the Monte Carlo (MC) α-k iteration method, lifting the need for an initial guess along with an improved convergence rate. To do that, a link is established between the actual physical parameters of the system and the α-eigenvalue in each iteration. Also, it is shown that the combination of currently used methods and our proposed algorithm would end to a reduced variance in the final result. The MC3 Monte Carlo code is empowered via several modules enabling us to perform a comparative analysis on the performance of α adjusting techniques. Several test cases are examined for the assessment of suggested scheme proving efficiency and robustness of the approach.
[en] Highlights: • A coupling between neutron transport and thermomechanics is performed. • A multiphysics approach, based on the Improved Quasi-static Method, is proposed. • Coupling techniques and time-step control strategies are tested in this frame. - Abstract: The quasi-static method is widely used for space- and time-dependent neutron transport problems. It is based on the factorization of the flux into the product of two functions, an “amplitude” depending only on time and a “shape” which depends on all variables. Thanks to this factorization, long time-steps can be used for the computation of the shape, leading to a substantial reduction of the calculation time. Two algorithms, based on the quasi-static factorization, can be found in the literature: the “Improved Quasi-static Method” (IQM), and the “Predictor-Corrector Quasi-static Method” (PCQM). In this paper we show, on the example of the Godiva experiment, that the IQM algorithm can be easily adapted to multi-physics simulations. Moreover, most of the common coupling or time-step control strategies are compatible with this algorithm and we test some of them here. In particular, a technique taken from existing codes with point-kinetic modules and based on feedback coefficients is found, in our case, to be especially efficient and gives precise and fast results. This shows that the multi-physics IQM presented in this paper is compatible with these existing codes, and may be a way to couple them with neutron transport solvers.
[en] Highlights: • Multi-level acceleration including MOC/NEM, Multigroup CMFD and One Group CMFD. • Generalized equivalence theory for the consistencies between 3 levels. • In-house developed linear solver and a innovated efficient Preconditioner for large scale parallel computing. - Abstract: A new 2D/1D method with multi-level generalized equivalence theory (GET) based coarse mesh finite difference (CMFD) acceleration was proposed for the whole core transport calculation in this paper. Fouressential features of this new 2D/1D methods are as follows: (1) Two new defined factors, nodal discontinuity factor (NDF) and modified diffusion coefficient factor (MDF), were defined in this new GET based CMFD method to achieve equivalence between CMFD and the transport solutions and especially insure that only positive coupling coefficients would occur in the CMFD linear system; (2) For accelerating the convergence of the CMFD, a multi-level acceleration scheme was implemented and an innovative self-developed RSILU preconditioned GMRES solver was developed to solve the CMFD linear system; (3) Within the new CMFD framework, 2D MOC and 1D two-node nodal expansion solvers were developed for 3D whole core transport calculation and the sub-plane technique was applied to minimize the nodal error successfully while maintain a reasonable computing time; (4) For implementation, transverse leakage splitting technique was applied to avoid the total source to become negative, and domain decomposition method based on MPI was implemented to take advantages of high performance clusters. The accuracy of this 2D/1D method via multi-level GET based CMFD and the effectiveness and acceleration performance of the multi-level CMFD method were examined for the well-known C5G7 benchmarks problems. The numerical results demonstrate that superior accuracy is achievable and the multi-level acceleration schemeis efficient and enhances the converge speed of both the GET based CMFD acceleration and the MOC calculation.
[en] Solution of the k-eigenvalue transport problem has been limited in lattice codes to the fundamental mode corresponding to the largest eigenvalue. Despite the fact that the higher order modes have no physical meaning, they can have significant uses in different applications. While the fundamental mode represents the asymptotic behaviour of the neutron flux, higher modes describe the small perturbations about it; hence, they can be employed in perturbation studies. Another important application of the higher modes is flux synthesis or mapping. Starting with a reference solution of the neutron flux at a coarse level and a number of modes at a finer level, detailed flux distribution can be reconstructed from a coarse solution. In this work, an implementation of a neutron flux modes solver in DRAGON is described. The solver is based on the QZ decomposition algorithm. The approach is described and results are presented. (author)
[en] In this paper, spacial domain-decomposed parallel Matrix MOC and relevant multi-domain coupled PGMRES accelerating algorithm were studied. In this algorithm, PGMRES from PETSc library was adopted to solve the angular flux of inner boundaries directly, thus improving the convergence rate. Numerical results demonstrated that the multi-domain coupled PGMRES algorithm keeps good accuracy and obtains great speed ratio. (authors)
[en] Highlights: • A new 3D neutron transport application (ARRC) is presented. • ARRC implements the recently developed Random Ray Method (TRRM). • A parallel domain decomposition scheme is developed and optimized. • Validation is performed on several 2D and 3D benchmarks. • ARRC is found to be a fast and accurate simulation tool for reactor modelling. - Abstract: A massively parallel implementation of a recently developed technique for numerically integrating the transport equation, The Random Ray Method (TRRM) (Tramm et al., 2017), is applied to several large reactor benchmark problems. The implementation, which is part of a new development called The Advanced Random Ray Code (ARRC), is one of the first parallel implementations of TRRM. Our goal is to better understand the accuracy and performance characteristics of TRRM on massive scale problems, and to provide community software that facilitates further algorithmic development and potentially its application to a broader class of problems. Key features of ARRC include extreme memory efficiency, domain decomposition, a task based parallel structure, and the ability to efficiently utilize Single Instruction Multiple Data (SIMD) vector units. These attributes lead to efficient performance on modern high performance computer (HPC) architectures, enabling the detailed simulation of reactor cores in three dimensions.
[en] Highlights: • The original and modified Kobayashi Benchmark Problems were solved using in-house code AETIUS. • The shape of the source region was modified to a peanut-shell shape to show the effectiveness of using unstructured tetrahedral mesh. • The AETIUS results showed good agreement with reference solutions. - Abstract: The discrete ordinates method (also called the SN method) has been widely used in radiation transport calculations. However, the ray effect and complicated geometry modeling are major shortcomings of the SN calculation compared to the Monte Carlo method. AETIUS is an in-house 3D neutron/photon transport code. It uses the first collision source method on a point or volume source and an unstructured tetrahedral mesh to overcome the two shortcomings mentioned above. A three-dimensional un-collided flux and first collision source code, FNSUNCL3, was previously developed for TORT in three-dimensional X-Y-Z geometry and its benchmark results on Kobayashi problems showed good agreement with the reference. We adapted the methodology used in FNSUNCL3 by modifying the volume source to several pseudo-point sources and summing the contributions from all pseudo-point sources. However, the AETIUS code uses unstructured tetrahedral mesh such that we can apply the first collision source method to any shape of volume sources. The AETIUS results for the original Kobayashi Benchmark Problems and for the Modified Kobayashi Benchmark Problem 2, are shown here to demonstrate the efficacy of using unstructured tetrahedral mesh. These new results show good agreement with reference results.