MCNP6: Getting a "10 particles got lost" error

[a1234]

MCNP6 gives me a "10 particles got lost" error when I try to run the attached input file modeling a 3x3 fuel lattice surrounded in coolant. As I understand it, this error is usually related to the geometry/surface definitions of each component, but I'm unsure of what the source of the error is. The output file says "there appears to be no cell on the other side of the surface from cell 11 at that point," which makes me think the issue stems from the way the lattice was defined.

I'd appreciate it if somebody could help me figure out the source of the issue, or perhaps help me interpret the output file. Thanks.

 

[berkeman]

when I try to run the attached input file

I'm not seeing any file attachment. Maybe the format of the file is preventing it from uploading. If so, change the suffix to ".txt" to upload it, and mention what the suffix should be changed back to in order to run it.

 

[a1234]

The Geometry.txt file extension should be changed to .i to run it in MCNP.

 

[Alex A]

In universe 2, the outside of the cladding isn't defined as a cell. ie +(surface)4. Fixing this does not fix everything, but it does help.

Your last line for the fill is 31113 instead of 33333. I don't understand lattices, is this correct? (changing it does not seem to help)

I'll take another look tomorrow.

 

[a1234]

Redefined cell 11 as being +4 and being material 3 (coolant), but still getting the same error.
Yes, the last line in the fill should have been 3 3 3 3 3.

 

[Alex A]

In this, cell 11 is still the lattice cell. I just made a new cell number for the missing volume.

Ok, mcplot to the rescue. Running with ipz on the command line let's us click to see a default plot in the interactive viewer. We can then click on an area to see what cell it's defined as. The command "pz 0" then shows us a slice. The is immediately wrong, there are only two fuel rods. When you specified the lattice you put the z's first. The right thing to do is probably be to not specify z limits in cell 11 at all, it's a 2D lattice. I see examples in the manual that do this so I think this is, at worst, fine. I then put the z limits into the cell being filled. This was helpful, not a total fix, I'm not 100% it isn't just a mcplot issue.

Next we have the problem that the 5x5 lattice isn't big enough to fill the volume you've told it to fill. This means there is a shell of volume around the core that isn't assigned to any cell. Fixing this is just means tweaking the geometry until it matches the real thing, if this is based on a real thing.

I think at that point the leaks stopped. I had a source overflow that needed me to change the initial k guess, but I've messed with a lot of stuff in order to get it running on my system and to make things easily visible in mcplot. Btw, your control rod tube is very very narrow. I don't think I needed to do anything else to make it work.

 

[a1234]

Thank you so much for the help, I was able to get it to work!