The problem with density units.（Materials.set_density）

User Support
1

Hello,

I converted the MCNP input content introduced by the ICSBEP handbook to the input card of OpenMC.
The density of OpenMC materials is set by MCNP setting density (material density == add each atomic density in the material),the result of the calculation is 1.02858 +/- 0.00100; then I change the material density to Materials.set_density(‘sum’), the result is 0.99872 +/- 0.00103,and very close to the MCNP result (1.0004±0.0008).
I don’t know what the reason is, can you tell me?
Atom_b_cm.py is the first described fiel, and sum.py is the changed file.

Best,
Tang

sum.py (3.06 KB)

atom_b_cm.py (3.26 KB)

2

Hello Tang,

It looks like the densities do not add up correctly for the fuel material. For “atom_b_cm.py” the total fuel density is set at 0.098 atom/b-cm. For “sum.py” the density adds up to 4.7214e-2 + 4.8872e-6 + 6.0830e-4 + 2.2531e-2 = 0.070 atom/b-cm. If you change the density in “atom_b_cm.py” to 0.07035 I expect you will find the same result.

Sterling

3

Thanks a lot!

Sterling Harper <smharper@mit.edu> 於 2019年4月27日 週六 上午12:11 寫道：