Benchmarking of MCNP for calculating dose rates at an interim storage facility for nuclear waste

During the operation of research facilities at Research Centre Jülich, Germany, nuclear waste is stored in drums and other vessels in an interim storage building on-site, which has a concrete shielding at the side walls. Owing to the lack of a well-defined source, measured gamma spectra were unfolded to determine the photon flux on the surface of the containers. The dose rate simulation, including the effects of skyshine, using the Monte Carlo transport code MCNP is compared with the measured dosimetric data at some locations in the vicinity of the interim storage building. The MCNP data for direct radiation confirm the data calculated using a point-kernel method. However, a comparison of the modelled dose rates for direct radiation and skyshine with the measured data demonstrate the need for a more precise definition of the source. Both the measured and the modelled dose rates verified the fact that the legal limits (<1 mSv a(-1)) are met in the area outside the perimeter fence of the storage building to which members of the public have access. Using container surface data (gamma spectra) to define the source may be a useful tool for practical calculations and additionally for benchmarking of computer codes if the discussed critical aspects with respect to the source can be addressed adequately.     

A comparison of skyshine computational methods

A variety of methods employing radiation transport and point-kernel codes have been used to model two skyshine problems. The first problem is a 1 MeV point source of photons on the surface of the earth inside a 2 m tall and 1 m radius silo having black walls. The skyshine radiation downfield from the point source was estimated with and without a 30-cm-thick concrete lid on the silo. The second benchmark problem is to estimate the skyshine radiation downfield from 12 cylindrical canisters emplaced in a low-level radioactive waste trench. The canisters are filled with ion-exchange resin with a representative radionuclide loading, largely 60Co, 134Cs and 137Cs. The solution methods include use of the MCNP code to solve the problem by directly employing variance reduction techniques, the single-scatter point kernel code GGG-GP, the QADMOD-GP point kernel code, the COHORT Monte Carlo code, the NAC International version of the SKYSHINE-III code, the KSU hybrid method and the associated KSU skyshine codes.     

Normalization of a collimated 14.7 MeV neutron source in a neutron spectrometry system for benchmark experiments

In the present study a method used to normalize a collimated 14.7 MeV neutron beam is introduced. It combined a measurement of the fast neutron scalar flux passing through the collimator, using a copper foil activation, with a neutron transport calculation of the foil activation per unit source neutron, carried out by the discrete-ordinates transport code DOT 4.2. The geometry of the collimated neutron beam is composed of a D-T neutron source positioned 30 cm in front of a 6 cm diameter collimator, through a 120 cm thick paraffin wall. The neutron flux emitted from the D-T source was counted by an NE-213 scintillator, simultaneously with the irradiation of the copper foil. Thus, the determination of the normalization factor of the D-T source is used for an absolute flux calibration of the NE-213 scintillator.The major contributions to the uncertainty in the determination of the normalization factor, and their origins, are discussed.     

The refined shielding design for the cyclotron room of the Buddhist Tzu Chi General Hospital

Full-scale Monte Carlo simulations of the cyclotron room of the Buddhist Tzu Chi General Hospital were carried out to improve the inadequate maze design. The double differential neutron source from the 18O(p,n)18F reaction was adopted for the calculation. The weight window variance reduction technique, where the weight window was set by applying the adjoint flux, has been implemented in the MCNP run to facilitate the calculation of the dose rates outside the cyclotron room. Dose rates including neutron and gamma-ray components were calculated for some maze shielding modifications.     

Control of the freezing interface motion in two-dimensional solidification processes using the adjoint method

The aim of this work is to calculate the optimum history of boundary cooling conditions that, in two-dimensional conduction driven solidification processes, results in a desired history of the freezing interface location/motion. The freezing front velocity and heat flux on the solid side of the front, define the obtained solidification microstructure that can be selected such that desired macroscopic mechanical properties and soundness of the final cast product are achieved. The so-called two-dimensional inverse Stefan design problem is formulated as an infinite-dimensional minimization problem. The adjoint method is developed in conjunction with the conjugate gradient method for the solution of this minimization problem. The sensitivity and adjoint equations are derived in a moving domain. The gradient of the cost functional is obtained by solving the adjoint equations backward in time. The sensitivity equations are solved forward in time to compute the optimal step size for the gradient method. Two-dimensional numerical examples are analysed to demonstrate the performance of the present method.     

Guaranteed error bounds on pointwise quantities of interest for transient viscodynamics problems

A new method is developed to obtain guaranteed error bounds on pointwise quantities of interest for linear transient viscodynamics problems. The calculation of strict error bounds is based on the concept of “constitutive relation error” (CRE) and the solution of an adjoint problem. The central and original point of this work is the treatment of the singularity in space and time introduced by the loading of the adjoint problem. Hence, the adjoint solution is decomposed into two parts: (i) an analytical part determined from Green’s functions; (ii) a residual part approximated with classical numerical tools (finite element method, Newmark integration scheme). The capabilities and the limits of the proposed approach are analyzed on a 2D example.     

An adjoint method for the inverse design of solidification processes with natural convection

This paper presents a finite element algorithm based on the adjoint method for the design of a certain class of solidification processes. In particular, the paper addresses the design of directional solidification processes for pure materials such that a desired freezing front heat flux and growth velocity are achieved. This is the first time that an infinite-dimensional continuum adjoint formulation is obtained and implemented for the solution of such inverse/design problems with moving boundaries and Boussinesq incompressible flow. The present design problem belongs to a category of inverse problems in which one is looking for the unknown conditions in part of the boundary, while overspecified boundary conditions are supplied in another part of the boundary (here the freezing interface). The solidification design problem is mathematically posed as a whole time-domain optimization problem. The gradient of the cost functional is calculated using the solution of an appropriately defined continuous adjoint problem. The minimization process is realized by the conjugate gradient method via the solutions of the direct, adjoint and sensitivity sub-problems. The proposed methodology is demonstrated with the solidification of an initially superheated liquid aluminum confined in a square mold. The non-uniformity in the casting product in the direction of gravity due to the existence of natural convection in the melt is emphasized. The inverse design problem is then posed as finding the appropriate spatial-temporal variations of the boundary heat flux on the vertical mold walls that can eliminate or reduce the effects of convection on the freezing interface heat fluxes and growth velocity. The numerical example demonstrates the accuracy and convergence of the adjoint formulation. Finally, open related research design problems are discussed. © 1998 John Wiley & Sons, Ltd.     

分群结构对IHNI-1堆动态参数计算结果的影响研究

基于WIMS和CITATION程序的计算结果,编制了动态参数计算程序CKPWC(calculating kinetic parameters based on WIMS and CITATION),对医院中子照射器Ⅰ型堆(in-hospital neutron irradiator mark 1 reactor,IHNI-1)的动态参数计算进行了研究.首先使用WIMS计算出均匀化栅元截面以及69群通量,再使用CITATION进行四群扩散计算,最后编制动态参数计算程序,计算了IHNI-1动态参数(缓发中子有效份βeff和中子代时间Λ).经过比较研究发现,分群结构对动态参数的计算结果有很大的影响.给出了计算IHNI-1缓发中子份额和中子代时间的最佳四群分群结构.使用文章中的最佳分群结构思想对西安脉冲堆动态参数进行了验证计算,计算结果与设计值符合一致,说明给出的IHNI-1动态参数计算结果具有一定的可信性.     

A fence line noble gas monitoring system for nuclear power plants

A noble gas monitoring system has been installed at Ontario Power Generation's Pickering Nuclear Generating Station (PNGS) near Toronto, Canada. This monitoring system allows a direct measure of air kerma from external radiation instead of calculating this based on plant emission data and meteorological models. This has resulted in a reduction in the reported effective dose from external radiation by a factor of at least ten. The system consists of nine self-contained units, each with a 7.6 cm x 7.6 cm (3 inch x 3 inch) NaI(TI) detector that is calibrated for air kerma. The 512-channel gamma ray spectral information is downloaded daily from each unit to a central computer where the data are stored and processed. A spectral stripping procedure is used to remove natural background variations from the spectral windows used to monitor xenon-133 (133Xe), xenon-135 (135Xe), argon-41 (41Ar), and skyshine radiation from the use of radiography sources. Typical monthly minimum detection limits in air kerma are 0.3 nGy for 133Xe, 0.7 nGy for 35Xe, 3 nGy for 41Ar and 2 nGy for skyshine radiation. Based on 9 months of continuous operation, the annualised air kerma due to 133Xe, 135Xe and 41Ar and skyshine radiation were 7 nGy, 8 nGy, 26 nGy and 107 nGy respectively.     

A FINITE POINT METHOD IN COMPUTATIONAL MECHANICS. APPLICATIONS TO CONVECTIVE TRANSPORT AND FLUID FLOW

The paper presents a fully meshless procedure fo solving partial differential equations. The approach termed generically the ‘finite point method’ is based on a weighted least square interpolation of point data and point collocation for evaluating the approximation integrals. Some examples showing the accuracy of the method for solution of adjoint and non-self adjoint equations typical of convective-diffusive transport and also to the analysis of compressible fluid mechanics problem are presented.     

Boundary optimal control of the Navier-Stokes equations--a numerical approach

Boundary optimal control problems of the Navier-Stokes equation are studied from a numerical point of view. When the adjoint variable method is used to minimize the objective function, the gradient of the objective function is not obtained accurately due to the insufficient regularity of the adjoint variable at the boundary. The resulting numerical error usually causes the conjugate gradient iteration to terminate prematurely. In the present investigation, a new method is developed that circumvents this difficulty with the adjoint variable method by converting the boundary optimal control problems to the distributed control problems. The present method is applied to two boundary optimal control problems, a driven cavity flow and a channel flow, and is found to solve the problems efficiently with sufficient accuracy.     

基于模糊聚类分析的适老健身设施功能集构建

目的 针对社区适老化健身设施品类单一、无法满足60～74岁老年人多样化健身需求等问题,提出利用模糊聚类分析法对适老健身设施进行功能集的构建,为适老健身设施模块化、集成化设计提供参考。方法 通过对目标老龄群体进行需求调研与权重计算,得到13项适老健身设施的二级功能模块,并从功能域、结构域、用户需求域等角度构建各模块关联性矩阵,利用三大子关联矩阵数据推导出综合关联矩阵Rc标准指数,将其作为模糊等价矩阵数据输入Matlab软件中进行模糊聚类分析并生成动态聚类树,以得出多组适老健身设施功能集合方案。结果 通过模糊聚类与动态聚类树分析,得到4种适老健身设施功能集合方案,同时从结构学角度对适老健身设施的接触面和支撑面进行分析,选取结构相似的适老健身设施进行集成化设计,最终得出适老健身设施的最佳功能集。结论 通过模糊聚类分析方法建立的适老健身设施功能集,能够有效解决社区老龄群体对健身设施的多样化需求,为后续适老健身设施设计提供了新的思路。     

A New GSOR Method for Generalised Saddle Point Problems

A novel generalised successive overrelaxation (GSOR) method for solving generalised saddle point problems is proposed, based on splitting the coefficient matrix. The proposed method is shown to converge under suitable restrictions on the iteration parameters, and we present some illustrative numerical results.     

双扫描雾化喷射成形工艺过程优化控制研究

本文采用“反推法”研究了雾化沉积工艺中关键参数的确定原则，并推导了双喷扫描过程中沉积平面上任意一点处金属质量流率与时间的关系。文中采用优化后的工艺参数进行了数学计算，并通过雾化沉积实验对计算结果进行了验证，对比结果证明采用“反推法”确定沉积工艺参数具有很高的计算效率和准确性，同时该结果可推广应用于任意数目喷嘴的雾化沉积工艺。     

On the use of the adjoint operator for source reconstruction in particle transport problems

In this work, the adjoint to the transport operator is used to estimate the spatial distribution of an isotropic neutral particles source in a homogeneous one-dimensional medium, from readings of internal detectors. An analytical discrete ordinates formulation, the ADO method, is applied to derive a spatially explicit solution for the adjoint flux. Simulations are performed for reconstructing Gaussian and piecewise localized sources. Numerical results indicate that the source estimates may be considered satisfactory although scalar fluxes are reconstructed more precisely.     

Entropy minimization in turbine cascade using continuous adjoint formulation

A complete continuous adjoint formulation is presented here for the optimization of the turbulent flow entropy generation rate through a turbine cascade. The adjoint method allows one to have many design variables, but still afford to compute the objective function gradient. The new adjoint system can be applied to different structured and unstructured grids as well as mixed subsonic and supersonic flows. For turbulent flow simulation, the k–ω shear-stress transport turbulence model and Roe's flux function are used. To ensure all possible shape models, a mesh-point method is used for design parameters, and an implicit smoothing function is implemented to avoid the generation of non-smoothed blades. To analyse the capability of the presented algorithm, the shape of a turbine cascade blade is redesigned and a few physical observations are made on how the scheme improves the blade performance.     

Automatic computed tomography patient dose calculation using DICOM header metadata

The present work describes a method that calculates the patient dose values in computed tomography (CT) based on metadata contained in DICOM images in support of patient dose studies. The DICOM metadata is preprocessed to extract necessary calculation parameters. Vendor-specific DICOM header information is harmonized using vendor translation tables and unavailable DICOM tags can be completed with a graphical user interface. CT-Expo, an MS Excel application for calculating the radiation dose, is used to calculate the patient doses. All relevant data and calculation results are stored for further analysis in a relational database. Final results are compiled by utilizing data mining tools. This solution was successfully used for the 2009 CT dose study in Luxembourg. National diagnostic reference levels for standard examinations were calculated based on each of the countries' hospitals. The benefits using this new automatic system saved time as well as resources during the data acquisition and the evaluation when compared with earlier questionnaire-based surveys.     

Estimating rotational iron losses in an induction machine

We present an assessment of the effect of rotational losses on an induction machine. The assessment provides an estimate of the iron losses in an induction machine by three methods, all of which rely on the output data of a two-dimensional finite-element method: 1) calculating iron losses as if they were produced by a purely alternating field; 2) calculating the iron losses by adding the losses produced by the orthogonal components of the flux density, as if the losses produced by these components were independent phenomena; 3) applying a correction factor based on experimental data to improve the rotational loss calculation. The correction factor is a function of the peak flux density value and the ratio of the major to the minor axis of the flux density loci. The third method represents the main contribution of this paper to the field and is explained in detail. Finally, a discussion of the results addresses two aspects: the location where rotational fields occur, and their impact on the total loss calculation.     

Solution of low p'eclet number heat transfer with viscous dissipation in the infinite axial region between parallel plates via functional analytic methods

Abstract

Functional analytic methods have been applied to the analysis of the extended Graetz problem with prescribed wall flux and viscous dissipation between parallel plates. First, the non‐self‐adjoint elliptic energy equation is decomposed into a set of first order partial differential equations to obtain a self‐adjoint formulism. Next, the induced eigenvalue problems are solved by applying an approximation method in a Hilbert space, and an algebraic characteristic equation is obtained. In addition, the expansion coefficients of the solutions on upstream and downstream regions can be explicitly obtained and unnecessary to match at the entrance.