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5-27Modeling Conversion Analysis for the Design of CiADS Li Jinyang,Zhang Lu,Yu Rui,Jiang Wei,Wang Dawei and Gu Long MCNPX is a general purpose Monte Carlo radiation transport code designed to track many particle types over broad ranges of energies and it has the potential to deal with Accelerator Driven System(ADS)problems.The neutronics design and analysis of ADS using MCNPX code is significantly complex mainly on constructing the three dimensional geometry model,especially when there is an additional spallation target coupled with the subcritical reactor constructed by abundant nested repeated structures in several levels.This modeling process has long been recognized as a time consuming,tedious and error-prone task,which is hard to master for novice users.Therefore, it is imperative to build a code system that can translate CAD models of ADS to the native language of MCNPX code.In this context of demand,a code system named CAD-PSMC(FreeCAD based parsing script for MCNPX code)has been developed to solve the CiADS modeling conversion problems.
Most of3-dimensional CSG models can be described by means of BGC and Boolean&Affine operations.However, for some weird structures with complex spline surfaces,although FreeCAD can handle these models,the MCNPX code does not have special functions to fully support these kinds of g
eometries.One expedient way to solve this problem is to transfer these models to its approximation ones in terms of a lot of mesh faces.
Fig.1(color online)Structure of STL format model used in CAD-PSMC code.
The complex model in the root node of hierarchical tree with a group index in FreeCAD,which cannot be easily described by means of the combination of basic primitives,will be treated as an integral model and exported into a Standard Transform Language(STL)file format.In this kind of format,for example,the reference model in Fig.1(a)is represented into a lot of triangular surfaces by means of BREP method instead of using CSG description, and each of these surfaces has been assigned with
an index named Block i(i∈[1,m])included with the information of facet normal and position of three vertexes as shown in Fig.1(b),the m indicates the total number of triangular surfaces in STLfile format.In order to transfer the STL format of complex models into the native CSG description in MCNPX code,a Ray-casting technology and Markov chain based iteration method have been proposed,in which, the corresponding throwing rays have been classified into three groups as shown in Fig.1(c),which parallel to the positive direction of x,y and z-axis respectively.
Three kinds of iterations have been designed in the ray-casting and Markov chain detection method,including the iteration for the throwing rays in three groups,the iteration for the data base of start points,and the iteration for all the intersecting surfaces along the vector direction of each throwing ray.For thefirst kind of iteration,a start points data base will be established including the geometry center information of all triangular facets in the reference STLfile.In the second kind of iteration,a branch condition has been set.For the group of throwing rays parallel with x-axis,only STL blocks data base will be used in collision detect process.And for other conditions, both STL and generated blocks data base will be used in collision detect process,in which,the GBDB is used to store the information of quadrangular facets generated in the ray-casting process.Additionally,before the next iteration,a Markov chain detection method will be used to check whether the current start poi
nt is satisfy with all the criterions.Finally,for the third kind of iteration,intersecting facets and corresponding start points will be removed from reference STLfile and SPDB respectively.Furthermore,the generated quadrangular surfaces in
transform和convert的区别
·212·2017 ray-casting process will be updated into the GBDB.Then polyhedrons will be generated along the vector direction of current throwing ray,and the corresponding facets will be translated into the native language of MCNPX code in terms of combination by Boolean operations.The three kinds of iterations will be repeated until all the sub-spaces of complex model are described by polyhedrons.
To test the modeling conversion capability of CAD-PSMC,a complex CiADS core structure has been employed as shown in Fig.2(a),which include abundant nested repeated structures in several levels and many independent complex structures with spline surfaces,for example,the wire-wounded fuel rods arranged in a top head structure (Fig.2(b)),slot-shaped entrance for liquid lead-bismuth eutectic(Fig.2(c))and complex bottom locking device (Fig.2(d)).This work is of high significance for the study of material property in complex devices,especially when the information of material displacement cross-section and mesh relatedflux distribution in complex geometry will be considered as the input conditions for mechanics analysis.The traditional input card mode provided by MCNPX c
annot deal with such kind of problem in the above examples.Although CAD-PSMC can describe this kind of model into unstructured mesh geometry,it is still a challenge task in translating the information of these structures to the native language of MCNPX.
Fig.2Complex CiADS core structure.
In this conversion process,the basic geometry and ray-casting methods in CAD-PSMC have been used to convert the complex CiADS core structure model,and the parameter of volume relevant difference has been employed to verify the quality of model conversion effect.The total selected structure number of units in CiADS core structure model is5976,and the tallied volume relevant differences are in the range of−1.4×10−8to1.0×10−8,which demonstrates that CAD-PSMC code can convert CiADS core structure model with good resolution.
5-28Validation of Neutron Evaluated Data Based on the
Experimental Reactivity Worth of Tungsten Target in CIADS
Jiang Wei and Gu Long
The granular tungsten spallation target is proposed by Institute of Modern Physics(IMP)as an innovative target. The granular tungsten target,which is placed in the center of the reactor,is impinged by the high-energy protons to produce spallation neutrons to maintain the stable operation of the system.Meanwhile,the spallation target, as structural material,has an effect on the reactor phys
ical parameters,such as neutronflux,neutron spectra and system reactivity.The mass fraction of tungsten is93%in the spallation target material,therefore the accuracy of tungsten cross section can impact directly on the reactor physical calculation in CIADS.In the past experiment on tungsten data evaluation,tungsten is generally used as reflecting layer or fuel diluent materials and is almost in fast-spectrum benchmark experiment setups.However,the relative study on the tungsten spallation materials in thermal-spectrum reactor are still scare.

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