Development of the automatic void generation module in GEOUNED conversion tool

doi:10.1016/j.fusengdes.2021.112366

Fusion Engineering and Design

Volume 168, July 2021, 112366

https://doi.org/10.1016/j.fusengdes.2021.112366 Get rights and content

Highlights

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Engineering CAD models need to be adapted to radiation transport computational codes.
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In highly complex models the automatic void generation is an essential feature.
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GEOUNED code integrates void cell fusion and independent void regions definition.
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New void features are studied converting an IFMIF-DONES CAD model into MCNP format.
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Fusion mode improves MCNP models and independent void regions help to structure them.

Abstract

The radiation transport simulation of complex nuclear facilities, such as ITER, involves the process to adapt the highly complex engineering CAD models to radiation transport computational codes. An essential feature of this process is the generation of void space. In this article, the automatic void generation module of the new GEOUNED conversion tool from CAD to MCNP geometry is presented. The module combines common approaches, such as the division of void space into void cells, with two new features: fusion of void cells and independent void regions definition with individual fill material assignation. In order to evaluate the performance of the module and the capabilities of the new features, the CAD model of the IFMIF-DONES Accelerator Systems (AS) is converted with different void mode configurations. The best configurations are determined comparing the computational performance and the void quality of the converted models.

Introduction

The radiation transport simulation of complex nuclear facilities involves the process to adapt the complex engineering CAD models to radiation transport computational codes. The codes based on Monte Carlo (MC) method are widely used owing to their accuracy and their 3D geometry definition capabilities. As example, MCNP (Monte Carlo N-Particle code) [1] is one of the most used MC codes for fusion applications. These codes use a specific Constructive Solid Geometry (CSG) definition which is not compatible with the CAD software applied in engineering. So, interface programs between CAD systems and MC transport simulation codes are needed. Two different approaches have been used to solve this incompatibility. The first one is based on the CAD model conversion into the CSG format used in the MC codes such as the codes MCAM [2], McCad [3], GEOMIT [4] and GEOUNED. The second one modifies the radiation transport codes to perform the particle transport directly in the CAD model. Examples of direct codes are DAGMC [5] and MCNP-BRL [6].

In highly complex models, such as ITER, the automatic void generation is one of the most important features. This feature is needed because engineering models only include the components of facilities as solids avoiding the space between them while in transport models all the space must be defined. In complex models, the definition of this space using CAD tools is tedious and prone to human error. Therefore, to face these models, interface programs must have an automatic void generation feature.

The article is devoted to one automatic void generator module, namely, that of GEOUNED conversion tool and it is organised as follows. In Section 2, GEOUNED tool is explained as well as the main structure and the two new features of the automatic void generation module. In Section 3, it is analysed the performance of the automatic void generation module and the capabilities of the new features with the conversion of the IFMIF-DONES (International Fusion Materials Irradiation Facility - DEMO Oriented Neutron Source) AS (Accelerator Systems) neutronic CAD model. Finally, in Section 4, the conclusions are presented.

Section snippets

GEOUNED automatic void generation module

GEOUNED is a new computational tool to convert complex CAD models into MCNP format and to improve the control that the user has over the conversion process as well as to automatize routine tasks. Fig. 1 represents its main steps.

GEOUNED loads the CAD model and then the decomposition algorithm decomposes each CAD solid into pieces, called basic solids, which have a MCNP direct conversion. Next, void space is defined as the complement to basic solids inside a bounding volume and this region is

Objectives and methodology

The automatic void generator module is analysed to study its performance, to confirm the expected behaviour of its modes and to compare the properties of the same CAD model converted with different void configurations.

The chosen neutronic model for this analysis is the IFMIF-DONES AS model and its building contains the deuteron accelerator, the Transport Line, the Beam Dump and other elements such as scrappers, magnets or shields [7]. This is a medium size model with more than 700 solids.

Fig. 7

Conclusions

In this article the GEOUNED automatic void generation module has been presented and it has been explained how this module combines common features, such as the division of void space into void cells, with two new features: fusion of void cells and user defined enclosure definition. The former reduces the complexity of the converted model while the later structures the void space defining independent void regions with their own fill material.

The performance of the automatic void generation

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work has been carried out partially within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. This work has been supported by the Ministerio de Ciencia e Innovación (MICINN), Spain under Plan Estatal I + D+i-Retos de la Sociedad, proyecto PID2019-109362RA-I00 and by

References (7)

Y. Wu et al.
CAD-based interface programs for fusion neutron transport simulation
Fusion Eng. Des.
(2009)
S. Sato
Progress of conversion system from CAD data to MCNP geometry data in Japan
Fusion Eng. Des.
(2010)
P.P. Wilson
Acceleration techniques for the direct use of CAD-based geometry in fusion neutronics analysis
Proceedings of the Ninth International Symposium on Fusion Nuclear Technology” Fusion Engineering and Design 85 (10–12)
(2010)

There are more references available in the full text version of this article.

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