MCNP 6.2: Fission Product Recoil/Transport

[TheNE]

TL;DR Summary

Does MCNP 6.2 produce recoil fission products (capable of transport)?

I am trying to simulate fission product ejection from thin fissile films in gas filled detectors (fission chamber). Does MCNP 6.2 produce recoil fission products that will be transported through the system?

I have enabled "heavy ion physics" (#), tried options 3 and 5 for NCIA on the neutron physics card, tried KCODE, BURN, and nothing seems to transport the fission products in my problem (measured with a F4:# tally in a void immediately beyond the fissile mass).

Thank you very much in advance for your assistance with this.

MCNP INPUT

c test for fp production and subsequent transport
c cell cards
1 1 -19 -10 VOL=523.6 imp:n=1 imp:#=1
2 0 -11 10 imp:n=1 imp:#=1
3 0 11 imp:n=0 imp:#=0

c surface cards
10 so 5
11 so 10
12 so 15

c data cards
c SDEF ERG=2.5E-6 PAR=1 POS= 6 0 0
c NPS 5E6
KCODE 1E6 0.4 0 10
KSRC 4.9 0 0
c BURN TIME=10 MAT=1 POWER=1
MODE N # P
PHYS:N 100 0 0 j j j 5 -1 j j j 0 0
MPHYS ON
c U-235 / rho=19g/cc
m1 92235 1
c ===================================
F14:# 2
F24:# 1
F34:P 2

 

[Astronuc]

As far as I know, MCNP handles neutrons and photons. For ion reactions, there is a code, SRIM, Stopping and Range of Ions in Matter. http://www.srim.org/
http://www.srim.org/SRIM Book (Review Pages).htm

 

[TheNE]

LANL coupled MCNPX into their MCNP6 release, including heavy ion transport - but I am dumbfounded on why a "simple" problem is not producing recoil FPs. NCIA, KCODE, and BURN don't even sample recoil KEs for the FPs. It is especially odd, in that the ENDF libraries include all the data to perform this sampling.

Thank you for your $0.02 though, Astronuc. I'll have to compare ion ranges from MCNP to SRIM sometime.

Satriani all the way.

 

[Astronuc]

a "simple" problem is not producing recoil FPs.

I don't believe the problem of "simulate fission product ejection from thin fissile films" is so simple. Firstly, one would have to track the fission product through the fissile material layer, then track the range in the gas, and possibly into the other solid surface.

There are two groups of fission products, one light (primarily A: 90-101) and the other heavy (A: 143-132). The light atoms have a longer range (4-6 microns) in UO₂, while the heavier atoms have a shorter range 3-5 microns. The ranges would be slightly lower in U-metal.

Some common fp pairs (with 2 prompt neutrons) for fission of U-235 (U-236* upon n-capture) based on fission yield (fy) are:

34-Se-86 + 58-Ce-148, fy = 0.012
38-Sr-97, 96, 95, 94 + 54-Xe-137, 138, 139, 140 fy = 0.0319, 0.0481, 0.0432, 0.0351
39-Y-99,97 + 53-I-135, 137 fy = 0.0293, 0.0262
40-Zr-100 + 52-Te-134, fy = 0.0622, most probable
41-Nb-101 + 51-Sb-133, fy = 0.0226

Of course there are other reactions, since we look for Kr-85, Kr-87 and Kr-88, as well as Xe-133, Xe-135 and Xe-138 (as well as I-131 through I-135), when failure fuel is present.

Then one would have to consider which of the two fps escapes for a given fission reaction. One could have a fission reaction in which both fp stay within the fissile coating, especially if both track parallel to the surface, or are more than ~ 6 microns below the surface, and one could have U atoms (or other fps) being knocked out of the surface.

The total kinetic energy of both fps is about 168 MeV, so less then 0.72 MeV/nucleon.

And of course, various nuclei are produced by n-capture or beta decay during service life.