Creating the geometry using MNCPX VisEd

[ugata88]

TL;DR

I'm having problems creating the geometry using MNCPX VisEd

I'm working on the MSFR design and want to calculate keff. I'm trying to use the MNCPX VisEd program included with MCNP 6.1 to create my geometry. The reactor I'm designing doesn't contain fuel rods or moderator structures. The molten salt fuel circulates within the cylindrical reactor core.

I'm having problems creating the geometry using MNCPX VisEd. VisEd allows for easy drawing of nested sphere, cylinder, or rectangular prism cells. However, when you want to draw a torus section within a cylinder or deviate from the geometries found in conventional reactor designs, creating surfaces and cells in CSG format is not user-friendly.

I've tried importing 3D geometries with the .SAT extension into VisEd from programs like ANSYS Design Modeler, SolidWorks, and AutoCAD, but I haven't been able to open the files. Can you recommend a method for creating an input file for the geometry below using VisED or another viewing/drawing program?

 

[DEvens]

My experience has been that VisEd is only useful to view your MCNP inputs. Trying to edit within VisEd is not worth it. For example, I would get frequent crashes that required me to delete a bunch of files created by VisEd in order to get it to start again.

If you are trying to use the 3D viewing feature of VisEd, I found it could only handle the simplest of geomtries. If you started getting things like hundreds of cells, or complicated structures like pipes through tanks, it got confused. In the 2-D view it usually did quite well.

The way I did it was to type in the MCNP input in a text editor. Then save the file. Then open it in VisEd.

The files I used for my main work were too large for VisEd and I had to use the built in plotting functions in MCNP. There is a special mode you start it in and it will graph your model. You can persuade it to produce limited diagnostic information during this as well. The commands for this are in the MCNP manual. It winds up looking very much like VisEd. I only ever got it to work with LINUX and only with the X-Windows emulator running. And then only with the help of the sys admin doing a lot of tweaking. I never got the plotter working on MS Windows.

You mentioned torus. There are some issues with torus shaped cells in MCNP. It loses particles. You should not try to use a torus to model a corner in a pipe, for example.

There was a project to convert a CAD program's file to MCNP. I don't know where they got to. This was before COVID, and the project was not very far. If you Google for it you might find it. I think it was a Japanese group. They were all set to send me a free copy of their prog, but then COVID caused everybody to be disrupted. We had an analysis program that could export its geometry to MCNP. The problem was it tended to produce thousands of cells when it should have only used two or three.

I am not sure but I have been told that the very latest version of MCNP has CAD ability. But I have never used it, so I could easily be completely wrong.

 

[ugata88]

I couldn't open the 3D CAD files I created above in Solidworks 2024, ANSYS 2024 Design Modeler, and AUTOCAD 2023 in MCNP 6.1 VisEd; it gave an ASCII error and didn't recognize my 3D designs. We recently purchased MCNP 6.3.1 for the project, and I'm hoping to use it for CAD files.

 

[Alex A]

I have read the version of VisEd supplied with 6.1 is a plot only version, not the full version. I think I read it's a separate package now instead of being supplied with the MCNP package. As far as I know SAT is the right format.
There have been many programs for putting CAD models into MCNP in the past. Mostly they seem to have vanished from the internet. Fluka/Cern FLAIR might be worth a try, it's intended for use with FLUKA, but it will save a model in MCNP format. I don't know if it will load any CAD formats but you might be able to construct your problem with the editor.

This sounds like a really cool project and I wish I could help more but I don't know this area.

Edit, Oh and you should check out DAGMC to see if it solves the problem
https://svalinn.github.io/DAGMC/index.html
I've never used it, but it purports to allow MCNP to simulate directly on CAD models.

 

[DEvens]

Re: Versions of VisEd. The executable that shipped with the last MCNP 5, and the one with up to MCNP 6.1, and the one that you get from the separate package, were identical. When I started having trouble I checked that I had the right version and compared all three. Down to the byte, identical.

Though I am Canadian, so might be under some kind of export restriction.

You won't be able to use CAD program files in MCNP without some sort of converter program. Either a built in utility in the CAD program, or another program. The format for CAD files will be drastically different. Different needs and different approach and different limitations.

You can check your CAD progs. Read the user manual or Google it. If no luck there you can Google up one of the mentioned projects to add CAD to MCNP.

If you find anything useful, even if it is a "that didn't work," I would be glad if you could post some info back here.