- Email: [email protected]
Status of the McCad geometry conversion tool and related visualization capabilities for 3D fusion neutronics calculations
Fusion Engineering and Design 88 (2013) 2210–2214
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Status of the McCad geometry conversion tool and related visualization capabilities for 3D fusion neutronics calculations D. Große, U. Fischer ∗ , K. Kondo, D. Leichtle, P. Pereslavtsev, A. Serikov Association KIT-Euratom, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany
h i g h l i g h t s • McCad – software tool developed at KIT for the automatic conversion of CAD models into the geometry representation of Monte Carlo particle transport codes.
• Open source software running under the Linux operating system and utilizing Open Cascade CAD kernel with the Qt4 libraries for the graphical user interface (GUI).
• Converted geometry models can be output in the syntax of MCNP and TRIPOLI of the Monte Carlo codes. • Related visualization capabilities, based on coupling of McCad with the ParaView software, allow to overlay mesh tally distributions to the CAD geometry. • McCad applied to solve fusion neutronics problems of ITER and the IFMIF neutron source.
a r t i c l e
i n f o
Article history: Received 11 September 2012 Received in revised form 14 February 2013 Accepted 26 February 2013 Available online 30 March 2013 Keywords: CAD Monte Carlo Neutronics ITER IFMIF
a b s t r a c t The McCad geometry conversion tool has been developed at KIT to enable the automatic conversion of CAD models into the semi-algebraic geometry representation as utilized in Monte Carlo particle transport simulations. McCad is entirely based on open source software, it is running under the Linux operating system and utilizes the Open Cascade CAD kernel with the Qt4 libraries for the graphical user interface (GUI). The converted geometry models can be output in the syntax of the Monte Carlo codes MCNP and TRIPOLI. Related visualization capabilities are based on the coupling of McCad with the ParaView software and allow to overlay mesh tally distributions to the CAD geometry. This enables perspective 3D representations or animations on the CAD geometry. The paper presents the current status of the McCad approach and its implementation, and discusses its capabilities, limitations as well as future development needs. The use of McCad for fusion neutronics applications is illustrated on the examples of the MCNP model generation for ITER Test Blanket Modules (TBM) and the test cell facility of the IFMIF neutron source including Monte Carlo shielding calculations using the converted models. © 2013 Elsevier B.V. All rights reserved.
1. Introduction The Monte Carlo (MC) method is a preferred computational technique for particle transport simulations in fusion technology applications. Full and detailed 3D geometry models can be used without the need for real approximations. The accuracy of the calculation is thus mainly affected by the statistical error of the calculation and the uncertainties of the nuclear cross-section data. Main drawbacks are related to the high computational effort required to achieve a sufficient statistical accuracy and the human effort needed for developing complex 3D geometry models. With the overwhelming progress in computer technology and the possibility to run Monte Carlo calculations in parallel on modern cluster
∗ Corresponding author. Tel.: +49 721 608 23407; fax: +49 721 608 23718. E-mail address: ulrich.fi[email protected] (U. Fischer). 0920-3796/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fusengdes.2013.02.146
machines, the computational effort is no longer a limitation. The manual modeling of a complex geometry with a Monte Carlo code, however, remains an extensive, time-consuming and error-prone task. A promising way to overcome this bottleneck is to make use of available CAD geometry data in the Monte Carlo calculations. This can be achieved by either converting the CAD data into the geometry representation used by Monte Carlo codes, or by the direct tracking of Monte Carlo particles on the CAD geometry. Several software tools have been developed over the past decade to make available CAD geometry data for Monte Carlo transport calculations. These include conversion tools like MCAM [1] and McCad [2], and the DAG-MCNP code [3] employing the direct particle tracking on the CAD geometry. This paper is devoted to the McCad conversion tool, developed at KIT to enable the automatic generation of Monte Carlo geometry models from CAD data. The current status of McCad is presented, its capabilities, limitations as well as future development needs
D. Große et al. / Fusion Engineering and Design 88 (2013) 2210–2214
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are discussed. The use of McCad for fusion neutronics applications is illustrated on the examples of the TBM and IFMIF model generation with subsequent shielding calculations performed with the MCNP and McDeLicious Monte Carlo codes. Visualization capabilities, enabled by coupling McCad trough suitable interfaces with the ParaView visualization software are also presented and demonstrated on application examples. 2. McCad approach for the conversion of CAD into Monte Carlo geometry models The McCad geometry conversion tool has been developed at KIT to enable the automatic conversion of CAD models into the semi-algebraic geometry representation as utilized in Monte Carlo particle transport simulations like MCNP [4] or TRIPOLI [5]. With the McCad approach, the input geometry is converted in two steps into a geometry description suitable for MC particle transport codes. In the first step the input geometry is decomposed into volumes that can be described by the Boolean combination of algebraic half-spaces. The overall geometry is not affected by the decomposition, i.e. the total volume content and the shape before and after the conversion are identical. In the second step McCad generates the void space which is not available in the CAD system but mandatory for the particle transport simulation codes. The conversion process is described in detail in [2]. McCad is coded in C++ based on object-oriented design patterns. It integrates the open source CAD kernel from Open CASCADE (OCC) [6] for all geometry related computations and CAD related file exchange. The build system makes use of the cross-platform makefile generator CMake. Its graphical user interface (GUI) is based on the cross-platform application and user interface framework Qt4. In its current version (0.3) McCad is available exclusively for Unix-like operating systems. Crucial for its operation is the integrated CAD kernel. Since end of 2011 the user community of Open CASCADE Technology (OCCT) decided to branch the official release of OCC for a better usability and shorter bug fixing cycles. The branch implements fixes for bugs discovered by the user community which will officially be fixed in the next public release of OCCT and provide a more comfortable installation procedure. McCad supports OCCT as well as the community edition (OCE). The latest development effort was mainly dedicated to improve the robustness of the code and increase the performance in terms of precision and speed. For the most crucial parts of the already existing code automated tests based on the google c++ testing framework have been implemented to increase the guarantee for the code’s correctness. 3. McCad geometry conversion for TRIPOLI McCad was originally devised as tool for the CAD to MCNP geometry conversion with the generation of an MCNP input deck at the backend. The support for other Monte Carlo codes does not require major changes to the already existing code. The differences in the conversion process for MCNP and TRIPOLI are minimal. Both codes require algebraic surfaces for the description of volumes, and both need the void spaces to be defined. The conversion from a CAD file to a MC geometry file basically consists of three steps as outlined in the schematic work flow shown in Fig. 1. The first step consists of reading and validating of the input geometry. The second step is devoted to the geometry conversion itself, i.e. the geometry decomposition and void generation. The final step is the export of the conversion result through the selected output filter. The first two steps are identical for all supported MC codes. For the extension of McCad to support the conversion to TRIPOLI, one new class had to be implemented to control
Fig. 1. Schematic work flow of the CAD to MC geometry conversion process within the McCad scheme.
the output for TRIPOLI. Furthermore, the printing function of each face surface had to be adapted to the TRIPOLI syntax. A simple material management system allows the assignment of available material and density information to the geometry cells. The correctness of the conversion process is tested by a direct comparison of the solid volumes after the decomposition as computed by the CAD kernel. McCad automatically produces a two-column list which links the volume number as given in the generated MC geometry file to the calculated volume. This calculation on the CAD level is exact within the machine precision. A stochastic volume computation with the TRIPOLI code using the converted model allows to compare the calculated volumes of all geometry cells with those provided by the CAD kernel before the conversion. The conversion to the TRIPOLI geometry representation has been successfully tested on the divertor used in the ITER CAD to MCNP benchmark [7].
4. Result visualization on CAD geometry With the mesh tally feature of MCNP5, high resolution spatial distributions of nuclear responses can be produced in a MC particle transport calculation. MCNP restricts the visualization of such distributions to 2D representations overlaid to the MCNP geometry. The interface programme mt2vtk, developed recently at KIT, converts MCNP’s mesh tally data into a file format based on the Visualization Toolkit (VTK) [8]. The vtk file format allows the three dimensional visualization of the mesh tally data overlaid to the CAD geometry using e.g. the ParaView [9] software. To this end, the CAD geometry model needs to be available in STEP format as depicted in Fig. 2. When starting with an MCNP model (i.e. no CAD geometry available), the MCNP geometry needs to be converted into CAD representation. Such a re-conversion is also provided with the McCad software although not all geometry options are currently supported such as some repeated structures (lattices), elliptical tori and generic quadric surfaces. The mt2vtk interface is coded in plain C++ making use of the boost framework. It uses CMake for the makefile generation and hence can be compiled for all established operating systems. No GUI is provided with the mt2vtk tool.
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Fig. 2. Flow scheme for the visualization of mesh tally distributions on CAD geometry using the ParaView software. Fig. 4. Map of the total neutron flux density in the test blanket port region overlaid to the McCad generated CAD geometry.
5. Application examples: ITER and IFMIF McCad is in routine use at KIT for the conversion of CAD geometry models for neutronics analyses with the MCNP code. It is also available to external users upon request. Major recent applications include the generation of a detailed MCNP model of the European Test Blanket (TBM) System integrated into the ITER A-lite model, and the development of a very detailed and comprehensive MCNP model of the IFMIF Target and Test Cell as detailed below. Prior to the conversion step, any CAD model needs to be adapted to the requirements for neutronics Monte Carlo calculations. MCNP e.g. uses Boolean forms of primitive solids and algebraic halfspaces for the geometry representation. CAD systems mainly use the boundary representation method to store geometric models of solids. The neutronics CAD model must use only analytical surfaces which are accepted by MCNP. Available MCNP surface types are planes, spheres, cylinders, cones, tori and a few macro bodies. In addition, modeling errors such as gaps and overlaps must be repaired, and geometrical simplifications as suitable for neutronics calculations, can be applied. McCad performs automatically model suitability and error checks, and, if possible, repairs them as described in Ref. [2]. Gaps and overlaps between boundary entities are detected during the geometry and topology error checking. Through McCad’s GUI, the
user can also modify and repair the geometry model. The next step is the conversion of the data which is followed by additional checks for overlaps among solids and their repair. The model is finally completed by voids and output in the standard MCNP or TRIPOLI syntax. This file can be used directly by MCNP/TRIPOLI after completion with other required input data. 5.1. HCPB/HCLL TBM system in ITER Within the framework of the European TBM Consortium of Associates, advanced designs for vertically arranged HCPB (HeliumCooled Pebble Bed) and the HCLL (Helium-Cooled Lithium–Lead) TBMs have been elaborated [10]. Engineering CAD models were provided for the test blanket port plug including all sub-systems such as the water-cooled steel frame, HCPB and HCLL TBM assemblies, shield modules, feeding pipes, etc. These models were adapted to the neutronics requirements as noted above. This step required a substantial CAD modeling effort using CATIA V5. The resulting neutronic CAD models were then automatically converted into the MCNP geometry representation. Remaining geometry errors were detected with MCNP test calculations and resolved manually.
Fig. 3. Scheme for the processing of the TBM port plug model and its integration into ITER.
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Fig. 5. Scheme for the processing of the IFMIF TTC model.
In a final step, the converted models were integrated into the equatorial test blanket port of the A-lite MCNP model of ITER [11]. This model represents a 40◦ ITER torus sector including various dummy ports for the integration of diagnostic tools, test objects, etc. Fig. 3 illustrates the full process starting with the CAD model of the TBM port plug, its decomposition on the CAD platform, the conversion to the MCNP geometry, and, finally, the integration into the A-lite model. A related visualization example is presented in Fig. 4 showing a perspective view of the 3D distribution of the total neutron flux density in the equatorial test blanket port region overlaid to the real (CAD) TBM port plug geometry model [12]. Such maps are obtained through the coupling of mesh tally data and the vtk based visualization software ParaView using the mt2vtk interface and the CAD model provided in STEP format.
again simplified and adapted to the neutronic requirements on the CAD platform, and, afterwards converted to the MCNP representation using McCad. The converted TTC model includes the test cell vessel with cover and all sub-systems such as the target assembly, the irradiation test modules with feeding pipes, lithium loop components, deuterium beam ducts, and the concrete shielding walls around the vessel. The final TTC MC model is rather complex and detailed, encompassing, after completion by void spaces, 17,520 geometry cells and 3234 surfaces. Fig. 5 shows the related processing steps in generating this model. As an application example, Fig. 6 shows the biological dose rate distribution as calculated with the McDeLicious code [15], an extension to MCNP, for the test cell at IFMIF full power operation [16].
5.2. IFMIF test cell model
6. Conclusion and outlook
Within the “Engineering Validation and Engineering Design Activities (EVEDA)” of the “International Fusion Materials Irradiation Facility (IFMIF)” project [13], which is being conducted in the framework of the Broader Approach agreement between Euratom and Japan [14], a detailed engineering CAD model of the Target and Test Cell (TTC) has been elaborated using CATIA V5. The model was
The status of the McCad conversion tool, developed at KIT to enable the automatic generation of Monte Carlo geometry models from CAD data, has been presented. McCad is entirely based on open source software, it is running under the Linux operating system and utilizes the Open Cascade CAD kernel with the Qt4 libraries for the graphical user interface (GUI). The converted geometry models can be output in the syntax of the Monte Carlo codes MCNP and TRIPOLI. Related visualization capabilities are based on the coupling of McCad with the ParaView software and allow to overlay mesh tally distributions to the CAD geometry. McCad is in routine use at KIT for the conversion of CAD geometry models for neutronics analyses with the MCNP code. It is available to external user upon request as test version under a GPL type license agreement. The McCad software package includes the source code, installation script and user instructions, a brief manual and test samples. The current McCad development efforts aim at improving the void generation algorithm, extend the capabilities for re-converting MCNP into CAD models, and enable the use of spline functions for the description of surfaces. It is planned, furthermore, to integrate McCad into the SALOME computation platform [17] to enable an efficient coupling of the geometry modeling process with neutronics, thermal hydraulics and structural analysis codes.
Fig. 6. 2D map of the biological dose rate [Sv/h] in the IFMIF TTC during operation (MCNP mesh tally plot).
References
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[1] L. Lu, Y.K. Lee, J.J. Zhang, Y. Li, Q. Zeng, Y.C. Wu, Development of Monte Carlo automatic modeling functions of MCAM for TRIPOLI-ITER application, Nuclear Instruments and Methods in Physics Research Section A 605 (2009) 384–387. [2] D. Grosse, H. Tsige-Tamirat, Current Status of the CAD Interface Program McCad for MC Particle Transport Calculations, in: Proceedings of International Conference on Mathematics, Computational Methods & Reactor Physics, Saratoga Springs, New York, May 3–7, 2009. [3] P.P.H. Wilson, T.J. Tautges, J.A. Kraftcheck, B.M. Smith, D.L. Henderson, Acceleration techniques for the direct use of CAD-based geometry in fusion neutronics analysis, Fusion Engineering and Design 85 (2010) 1759–1765. [4] X. Monte Carlo Team, MCNP – A General Monte Carlo N-Particle Transport Code (Version 5, Vol. I), Report LA-UR-03-1987, 24 April 2003. (Revised 10/3/05). [5] O. Petit, F.X. Hugot, Y.K. Lee, C. Jouanne, A. Mazzolo, TRIPOLI-4 Version 4 User Guide, CEA-R-6169 (2008), http://www.nea.fr/abs/html/nea-1716.html [6] http://www.opencascade.org [7] U. Fischer, H. Iida, Y. Li, M. Loughlin, S. Sato, A. Serikov, et al., Use of CAD generated geometry data in Monte Carlo transport calculations for ITER, Fusion Science and Technology 56 (2009) 702–709. [8] http://www.vtk.org [9] http://www.paraview.org [10] L.V. Boccaccini, A. Aiello, O. Bede, F. Cismondi, L. Kosek, T. Ilkei, et al., Present status of the conceptual design of the EU test blanket systems, Fusion Engineering and Design 86 (2011) 478–483.
[11] U. Fischer, D. Grosse, F. Moro, P. Pereslavtsev, L. Petrizzi, R. Villari, et al., Integral approach for neutronics analyses of the European test blanket modules in ITER, Fusion Engineering and Design 86 (2011) 2176– 2179. [12] P. Pereslavtsev, U. Fischer, D. Grosse, D. Leichtle, M. Majerle, Shutdown dose rate analysis for the European TBM system in ITER, Fusion Engineering and Design 87 (2012) 493–497. [13] H. Matsumuto, Fusion Technology Activities through the Broader Approach IFMIF-EVEDA Project, in: 20th Topical Meeting on the Technology of Fusion Energy, Nashville, August 27–31, 2012. [14] Y. Okumura, Present Status and Achievements of Broader Approach Activities, in: 20th Topical Meeting on the Technology of Fusion Energy, Nashville, August 27–31, 2012. [15] S.P. Simakov, U. Fischer, K. Kondo, P. Pereslavstev, The McDeLicious approach for the D-Li neutron source term modeling in IFMIF neutronics calculations, Fusion Science and Technology 62 (1) (2012) 240–245. [16] K. Kondo, F. Arbeiter, U. Fischer, D. Grosse, V. Heinzel, A. Klix, et al., Neutronic analysis for the IFMIF Target Test Cell using a new CAD-based geometry model, Fusion Engineering and Design 87 (2012) 983–988. [17] http://www.salome-platform.org/
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Status of the McCad geometry conversion tool and related visualization capabilities for 3D fusion neutronics calculations D. Große, U. Fischer ∗ , K. Kondo, D. Leichtle, P. Pereslavtsev, A. Serikov Association KIT-Euratom, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany
h i g h l i g h t s • McCad – software tool developed at KIT for the automatic conversion of CAD models into the geometry representation of Monte Carlo particle transport codes.
• Open source software running under the Linux operating system and utilizing Open Cascade CAD kernel with the Qt4 libraries for the graphical user interface (GUI).
• Converted geometry models can be output in the syntax of MCNP and TRIPOLI of the Monte Carlo codes. • Related visualization capabilities, based on coupling of McCad with the ParaView software, allow to overlay mesh tally distributions to the CAD geometry. • McCad applied to solve fusion neutronics problems of ITER and the IFMIF neutron source.
a r t i c l e
i n f o
Article history: Received 11 September 2012 Received in revised form 14 February 2013 Accepted 26 February 2013 Available online 30 March 2013 Keywords: CAD Monte Carlo Neutronics ITER IFMIF
a b s t r a c t The McCad geometry conversion tool has been developed at KIT to enable the automatic conversion of CAD models into the semi-algebraic geometry representation as utilized in Monte Carlo particle transport simulations. McCad is entirely based on open source software, it is running under the Linux operating system and utilizes the Open Cascade CAD kernel with the Qt4 libraries for the graphical user interface (GUI). The converted geometry models can be output in the syntax of the Monte Carlo codes MCNP and TRIPOLI. Related visualization capabilities are based on the coupling of McCad with the ParaView software and allow to overlay mesh tally distributions to the CAD geometry. This enables perspective 3D representations or animations on the CAD geometry. The paper presents the current status of the McCad approach and its implementation, and discusses its capabilities, limitations as well as future development needs. The use of McCad for fusion neutronics applications is illustrated on the examples of the MCNP model generation for ITER Test Blanket Modules (TBM) and the test cell facility of the IFMIF neutron source including Monte Carlo shielding calculations using the converted models. © 2013 Elsevier B.V. All rights reserved.
1. Introduction The Monte Carlo (MC) method is a preferred computational technique for particle transport simulations in fusion technology applications. Full and detailed 3D geometry models can be used without the need for real approximations. The accuracy of the calculation is thus mainly affected by the statistical error of the calculation and the uncertainties of the nuclear cross-section data. Main drawbacks are related to the high computational effort required to achieve a sufficient statistical accuracy and the human effort needed for developing complex 3D geometry models. With the overwhelming progress in computer technology and the possibility to run Monte Carlo calculations in parallel on modern cluster
∗ Corresponding author. Tel.: +49 721 608 23407; fax: +49 721 608 23718. E-mail address: ulrich.fi[email protected] (U. Fischer). 0920-3796/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fusengdes.2013.02.146
machines, the computational effort is no longer a limitation. The manual modeling of a complex geometry with a Monte Carlo code, however, remains an extensive, time-consuming and error-prone task. A promising way to overcome this bottleneck is to make use of available CAD geometry data in the Monte Carlo calculations. This can be achieved by either converting the CAD data into the geometry representation used by Monte Carlo codes, or by the direct tracking of Monte Carlo particles on the CAD geometry. Several software tools have been developed over the past decade to make available CAD geometry data for Monte Carlo transport calculations. These include conversion tools like MCAM [1] and McCad [2], and the DAG-MCNP code [3] employing the direct particle tracking on the CAD geometry. This paper is devoted to the McCad conversion tool, developed at KIT to enable the automatic generation of Monte Carlo geometry models from CAD data. The current status of McCad is presented, its capabilities, limitations as well as future development needs
D. Große et al. / Fusion Engineering and Design 88 (2013) 2210–2214
2211
are discussed. The use of McCad for fusion neutronics applications is illustrated on the examples of the TBM and IFMIF model generation with subsequent shielding calculations performed with the MCNP and McDeLicious Monte Carlo codes. Visualization capabilities, enabled by coupling McCad trough suitable interfaces with the ParaView visualization software are also presented and demonstrated on application examples. 2. McCad approach for the conversion of CAD into Monte Carlo geometry models The McCad geometry conversion tool has been developed at KIT to enable the automatic conversion of CAD models into the semi-algebraic geometry representation as utilized in Monte Carlo particle transport simulations like MCNP [4] or TRIPOLI [5]. With the McCad approach, the input geometry is converted in two steps into a geometry description suitable for MC particle transport codes. In the first step the input geometry is decomposed into volumes that can be described by the Boolean combination of algebraic half-spaces. The overall geometry is not affected by the decomposition, i.e. the total volume content and the shape before and after the conversion are identical. In the second step McCad generates the void space which is not available in the CAD system but mandatory for the particle transport simulation codes. The conversion process is described in detail in [2]. McCad is coded in C++ based on object-oriented design patterns. It integrates the open source CAD kernel from Open CASCADE (OCC) [6] for all geometry related computations and CAD related file exchange. The build system makes use of the cross-platform makefile generator CMake. Its graphical user interface (GUI) is based on the cross-platform application and user interface framework Qt4. In its current version (0.3) McCad is available exclusively for Unix-like operating systems. Crucial for its operation is the integrated CAD kernel. Since end of 2011 the user community of Open CASCADE Technology (OCCT) decided to branch the official release of OCC for a better usability and shorter bug fixing cycles. The branch implements fixes for bugs discovered by the user community which will officially be fixed in the next public release of OCCT and provide a more comfortable installation procedure. McCad supports OCCT as well as the community edition (OCE). The latest development effort was mainly dedicated to improve the robustness of the code and increase the performance in terms of precision and speed. For the most crucial parts of the already existing code automated tests based on the google c++ testing framework have been implemented to increase the guarantee for the code’s correctness. 3. McCad geometry conversion for TRIPOLI McCad was originally devised as tool for the CAD to MCNP geometry conversion with the generation of an MCNP input deck at the backend. The support for other Monte Carlo codes does not require major changes to the already existing code. The differences in the conversion process for MCNP and TRIPOLI are minimal. Both codes require algebraic surfaces for the description of volumes, and both need the void spaces to be defined. The conversion from a CAD file to a MC geometry file basically consists of three steps as outlined in the schematic work flow shown in Fig. 1. The first step consists of reading and validating of the input geometry. The second step is devoted to the geometry conversion itself, i.e. the geometry decomposition and void generation. The final step is the export of the conversion result through the selected output filter. The first two steps are identical for all supported MC codes. For the extension of McCad to support the conversion to TRIPOLI, one new class had to be implemented to control
Fig. 1. Schematic work flow of the CAD to MC geometry conversion process within the McCad scheme.
the output for TRIPOLI. Furthermore, the printing function of each face surface had to be adapted to the TRIPOLI syntax. A simple material management system allows the assignment of available material and density information to the geometry cells. The correctness of the conversion process is tested by a direct comparison of the solid volumes after the decomposition as computed by the CAD kernel. McCad automatically produces a two-column list which links the volume number as given in the generated MC geometry file to the calculated volume. This calculation on the CAD level is exact within the machine precision. A stochastic volume computation with the TRIPOLI code using the converted model allows to compare the calculated volumes of all geometry cells with those provided by the CAD kernel before the conversion. The conversion to the TRIPOLI geometry representation has been successfully tested on the divertor used in the ITER CAD to MCNP benchmark [7].
4. Result visualization on CAD geometry With the mesh tally feature of MCNP5, high resolution spatial distributions of nuclear responses can be produced in a MC particle transport calculation. MCNP restricts the visualization of such distributions to 2D representations overlaid to the MCNP geometry. The interface programme mt2vtk, developed recently at KIT, converts MCNP’s mesh tally data into a file format based on the Visualization Toolkit (VTK) [8]. The vtk file format allows the three dimensional visualization of the mesh tally data overlaid to the CAD geometry using e.g. the ParaView [9] software. To this end, the CAD geometry model needs to be available in STEP format as depicted in Fig. 2. When starting with an MCNP model (i.e. no CAD geometry available), the MCNP geometry needs to be converted into CAD representation. Such a re-conversion is also provided with the McCad software although not all geometry options are currently supported such as some repeated structures (lattices), elliptical tori and generic quadric surfaces. The mt2vtk interface is coded in plain C++ making use of the boost framework. It uses CMake for the makefile generation and hence can be compiled for all established operating systems. No GUI is provided with the mt2vtk tool.
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Fig. 2. Flow scheme for the visualization of mesh tally distributions on CAD geometry using the ParaView software. Fig. 4. Map of the total neutron flux density in the test blanket port region overlaid to the McCad generated CAD geometry.
5. Application examples: ITER and IFMIF McCad is in routine use at KIT for the conversion of CAD geometry models for neutronics analyses with the MCNP code. It is also available to external users upon request. Major recent applications include the generation of a detailed MCNP model of the European Test Blanket (TBM) System integrated into the ITER A-lite model, and the development of a very detailed and comprehensive MCNP model of the IFMIF Target and Test Cell as detailed below. Prior to the conversion step, any CAD model needs to be adapted to the requirements for neutronics Monte Carlo calculations. MCNP e.g. uses Boolean forms of primitive solids and algebraic halfspaces for the geometry representation. CAD systems mainly use the boundary representation method to store geometric models of solids. The neutronics CAD model must use only analytical surfaces which are accepted by MCNP. Available MCNP surface types are planes, spheres, cylinders, cones, tori and a few macro bodies. In addition, modeling errors such as gaps and overlaps must be repaired, and geometrical simplifications as suitable for neutronics calculations, can be applied. McCad performs automatically model suitability and error checks, and, if possible, repairs them as described in Ref. [2]. Gaps and overlaps between boundary entities are detected during the geometry and topology error checking. Through McCad’s GUI, the
user can also modify and repair the geometry model. The next step is the conversion of the data which is followed by additional checks for overlaps among solids and their repair. The model is finally completed by voids and output in the standard MCNP or TRIPOLI syntax. This file can be used directly by MCNP/TRIPOLI after completion with other required input data. 5.1. HCPB/HCLL TBM system in ITER Within the framework of the European TBM Consortium of Associates, advanced designs for vertically arranged HCPB (HeliumCooled Pebble Bed) and the HCLL (Helium-Cooled Lithium–Lead) TBMs have been elaborated [10]. Engineering CAD models were provided for the test blanket port plug including all sub-systems such as the water-cooled steel frame, HCPB and HCLL TBM assemblies, shield modules, feeding pipes, etc. These models were adapted to the neutronics requirements as noted above. This step required a substantial CAD modeling effort using CATIA V5. The resulting neutronic CAD models were then automatically converted into the MCNP geometry representation. Remaining geometry errors were detected with MCNP test calculations and resolved manually.
Fig. 3. Scheme for the processing of the TBM port plug model and its integration into ITER.
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Fig. 5. Scheme for the processing of the IFMIF TTC model.
In a final step, the converted models were integrated into the equatorial test blanket port of the A-lite MCNP model of ITER [11]. This model represents a 40◦ ITER torus sector including various dummy ports for the integration of diagnostic tools, test objects, etc. Fig. 3 illustrates the full process starting with the CAD model of the TBM port plug, its decomposition on the CAD platform, the conversion to the MCNP geometry, and, finally, the integration into the A-lite model. A related visualization example is presented in Fig. 4 showing a perspective view of the 3D distribution of the total neutron flux density in the equatorial test blanket port region overlaid to the real (CAD) TBM port plug geometry model [12]. Such maps are obtained through the coupling of mesh tally data and the vtk based visualization software ParaView using the mt2vtk interface and the CAD model provided in STEP format.
again simplified and adapted to the neutronic requirements on the CAD platform, and, afterwards converted to the MCNP representation using McCad. The converted TTC model includes the test cell vessel with cover and all sub-systems such as the target assembly, the irradiation test modules with feeding pipes, lithium loop components, deuterium beam ducts, and the concrete shielding walls around the vessel. The final TTC MC model is rather complex and detailed, encompassing, after completion by void spaces, 17,520 geometry cells and 3234 surfaces. Fig. 5 shows the related processing steps in generating this model. As an application example, Fig. 6 shows the biological dose rate distribution as calculated with the McDeLicious code [15], an extension to MCNP, for the test cell at IFMIF full power operation [16].
5.2. IFMIF test cell model
6. Conclusion and outlook
Within the “Engineering Validation and Engineering Design Activities (EVEDA)” of the “International Fusion Materials Irradiation Facility (IFMIF)” project [13], which is being conducted in the framework of the Broader Approach agreement between Euratom and Japan [14], a detailed engineering CAD model of the Target and Test Cell (TTC) has been elaborated using CATIA V5. The model was
The status of the McCad conversion tool, developed at KIT to enable the automatic generation of Monte Carlo geometry models from CAD data, has been presented. McCad is entirely based on open source software, it is running under the Linux operating system and utilizes the Open Cascade CAD kernel with the Qt4 libraries for the graphical user interface (GUI). The converted geometry models can be output in the syntax of the Monte Carlo codes MCNP and TRIPOLI. Related visualization capabilities are based on the coupling of McCad with the ParaView software and allow to overlay mesh tally distributions to the CAD geometry. McCad is in routine use at KIT for the conversion of CAD geometry models for neutronics analyses with the MCNP code. It is available to external user upon request as test version under a GPL type license agreement. The McCad software package includes the source code, installation script and user instructions, a brief manual and test samples. The current McCad development efforts aim at improving the void generation algorithm, extend the capabilities for re-converting MCNP into CAD models, and enable the use of spline functions for the description of surfaces. It is planned, furthermore, to integrate McCad into the SALOME computation platform [17] to enable an efficient coupling of the geometry modeling process with neutronics, thermal hydraulics and structural analysis codes.
Fig. 6. 2D map of the biological dose rate [Sv/h] in the IFMIF TTC during operation (MCNP mesh tally plot).
References
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