MCNP6.2 - SSW and surfaces defining universe boundaries

[19matthew89]

TL;DR Summary

Is SSW card able to track neutrons crossing surfaces defining universes?

Hi everyone,

I am using SSW card.
Although the manual is very clear about the fact that the cells used in SSW card have to belong to the lowest level, the manual is not that clear the surfaces.
Is SSW able to track particles crossing surfaces defining higher level universes?

Let's assume this code:

1 1  -1.0 10:-11
2 1  -1.0 11 -10 FILL=20
3 2  -2.7 -12 U=20
4 1  -1.0 12  U=20

C Surfaces
10 PZ 50
11 PZ -50
12 CZ 2

C Materials
M1      1001      0.6665667   $water                                                                   
        1002      0.000100                                                                       
        8016      0.3332063                                                                       
        8017      0.000127
      
M2      13027     1   $Al

May I write

 SSW -12 (3) -10 (3) 11 (3)

if I want to record all the particle entering the cylinder of basis at +50, -50 and of radius 2?
Or do I need to have auxiliary planes used in the universe U=20?

Moreover if I need to track particles through surfaces which have been transformed first via a TRCL, do I need to give the original surface, or the modified one. For instance, in the example above let's assume I applied a transformation TRCL at the cell 3, which surface do I need to specify

 SSW -3012 (3)

if I want to track the particles accross the lateral surface? Because I'd expect so, but when I tried a simple run it gave me error exactly saying that "surface 3012 not defined". So I am a bit puzzled.

Thanks in advance

 

[member38644]

Hello,

Thank you for your question about MCNP6.2 and SSW card. The SSW card is used to define a special weight window for a specific cell or group of cells. The surfaces used in the SSW card should belong to the lowest level of the cell hierarchy. This means that the surfaces should be defined in the same cell or in a cell below the cell where the SSW card is used.

In your example code, the surfaces 10, 11, and 12 are defined in cell 1, which is the lowest level cell. So, you can use these surfaces in the SSW card for cell 1. However, if you want to use the same surfaces in the SSW card for cell 3, you will need to define them again in cell 3 or in a lower level cell. This is because cell 3 is above cell 1 in the cell hierarchy.

For your second question, you can write SSW -12 (3) -10 (3) 11 (3) to track particles entering the cylinder at +50, -50, and of radius 2. You do not need to use auxiliary planes in the universe U=20 for this.

If you need to track particles through transformed surfaces, you should use the original surface in the SSW card. In your example, you should use SSW -3012 (3) to track particles across the lateral surface after applying the transformation TRCL at cell 3.

I hope this helps clarify your questions. Please refer to the MCNP manual for more detailed information on using the SSW card. Thank you.