I was hoping you guys could help me with transient simulations. I read a lot of stuff here but I don't think there are any posts covering my questions.
I am running C5G7 benchmark simulations. The benchmark is supercritical by definition (k_eff=1.17129); so in order to run the transients I have to limit them and I decided to do it by using gcut. As it turns out, depending on which gcut value I use, I get different fission rate values. You can see below the fission rate values I got for a 0.01s transient without any changes to the initial state (initial fission rate was 3.05E+10 ± 8.20E-06):
gcut / fission rate
15 / 1.40E+08 ± 0.00317
30 / 1.45E+09 ± 0.00754
45 / 1.23E+10 ± 0.03956
60 / 1.05E+11 ± 0.05976
I then increased the boron content to try and run a subcritical transient simulation (k_eff=0.98631) so I wouldn't have to limit it with gcut, and once again I got a weird value: initial fission rate was 3.04E+10 ± 1.80E-06 and the transient fission rate was 1.01012E+08 ± 0.01073. Again, no changes were made on the geometry/materials.
I also tried increasing population for all the cases, which didn't affect the fission rate. I used in all inputs:
Code: Select all
set delnu 1 set bala 1 set gcu -1 set impl 0 0 0