I'm trying to calculate heat deposition fractions in a simple geometry using the dr -4 and dr -8 response functions. From what I understand, dr -4 includes all neutron-driven reactions that produce heat, including fission and captures. dr -8 should be just fissions, and thus always less than dr -4. For some reason, using the below input, I see a dr -8 detector giving higher output than a dr -4 on the same material, both with volumes normalized correctly.

In this very simple geometry (3 concentric cubes), I set the power to 20 kilowatts (set power 20e3), and then let serpent run.

Code: Select all

```
set title "Simple heat deposition"
set acelib "sss_endfb7u.xsdata"
set declib "sss_endfb7.dec"
set nfylib "sss_endfb7.nfy"
% UMo fuel
mat fuel -17.0 vol 512.
92235.06c 80.0
Mo-nat.06c 20.0
% iron metal and some hydrogen
mat iron -13.0 vol 1352.
1001.06c .1
Fe-nat.06c .9
% I acknowledge that water S(a,b) libs shouldnt be used with zirc hydride...
mat zrh -5.6 moder hsab 1001 vol 2232.
Zr-nat.06c 1.0
1001.06c 1.6
therm hsab lwj3.11t
% Cube of UMo fuel encased in zirc hydride and iron
surf 1 cuboid -4.0 4.0 -4.0 4.0 -4.0 4.0
surf 2 cuboid -7 7 -7 7 -7 7
surf 3 cuboid -8 8 -8 8 -8 8
set bc 2
cell 1 0 fuel -1
cell 2 0 zrh 1 -2
cell 3 0 iron 2 -3
cell 4 0 outside 3
det modNtPow dr -4 zrh dv 2232.
det fuelNeutPower dr -4 fuel dv 512.
det fuelFissPower dr -8 fuel dv 512.
det shieldNeutPower dr -4 iron dv 1352
% 20 kilowatts
set power 20e3
plot 1 500 500
mesh 1 500 500
set pop 2000 50 10
```

Code: Select all

```
DETmodNtPow = [
1 1 1 1 1 1 1 1 1 1 3.09235E-01 0.00465
];
DETfuelNeutPower = [
1 1 1 1 1 1 1 1 1 1 2.92318E+03 0.00689
];
DETfuelFissPower = [
1 1 1 1 1 1 1 1 1 1 3.33515E+03 0.00690
];
DETshieldNeutPower = [
1 1 1 1 1 1 1 1 1 1 3.52345E+01 0.00737
];
```

Any help is greatly appreciated!