Why Does MCNP Show Absorptions in a Stainless Steel Cell with No Fuel?

[Gold13]

I am currently using KCode and modeling a fuel array (Lattice), reflector array (Lattice), and a Stainless steel reflector (Cell filled with Stainless steel, simple geometry). The cells are situated right next to one another, such as 3 squares of similar sizes which make a rectangle. All surrounded by perfect reflector boundaries except past the stainless steel cell.

Originally I was studying the albedo of different materials in the reflector array. I was then tasked with seeing what absorptions were occurring, other than fission. I used the F4 detector and then added the Fm4 (cell multiplier). I ran it got results, and then tried some tests for sanity.

My scenario/question: I ran the multiplier card out in the stainless steel cell and asked it for interactions (absorptions other than fission) with my fuel material. I expected there to be none bc there is no fuel present and MCNP printed that there were interactions. So, has anyone used this card before and maybe is there a simple explanation as to why I would see these results?

 

[_coyote_]

My understanding is that the Fm4 card is used to determine the total number of interactions within a certain cell. It can then be used to assess the neutron flux in the cell. So, I'm assuming the results I got were from the neutrons coming from the surrounding cells and being absorbed by the stainless steel wall. This would suggest that the neutrons were spilling out of the fuel array and into the stainless steel cell, which would make sense since the cells are right next to each other.

 

[raining Pete]

Hi there,

I haven't personally used the multiplier card in MCNP before, but from what I understand, it is used to calculate the number of secondary particles produced in a cell. So even though there is no fuel present in the stainless steel cell, there may still be interactions happening between the particles and the steel. This could be due to scattering or other types of interactions.

Another possibility is that there could be some small amount of impurities or contaminants in the stainless steel that are causing these interactions. Have you tried running the simulation with a different material for the stainless steel cell to see if you get the same results?

I would also suggest checking the input parameters and making sure everything is set up correctly. Sometimes small errors or typos can lead to unexpected results.

Hopefully this helps a bit. Good luck with your simulation!