RE: Stack Overflow Termination in fission experiment

Dear Jack

I ran your problem and observed the same issue, it runs with lead but
exceeds the size of the stack when using fissile material (U233). I
tried to use the LOW-NEUT card (WHAT (6)) to artificially limit the
fission neutron yield to 1 neutron (with a proportionally increased
weight) to limit the chain reaction. It did not solve the problem. I
then decreased the density of U233 to 0.05 g/cm3 as I suspected your
problem to be close to criticality. It did work in that case, in the
output file I had the following :

 Number of secondaries generated in inelastic interactions per beam =
particle:

 Prompt radiation Radioactive decays

   6.2000E+01 (100.%) 0.0000E+00 (100.%)

   3.4000E+00 ( 5.5%) 0.0000E+00 ( 0.0%) PROTON

   1.7800E+01 (28.7%) 0.0000E+00 ( 0.0%) PHOTON

   3.9900E+01 (64.4%) 0.0000E+00 ( 0.0%) NEUTRON

which seems ok to me starting with 1 GeV proton. However I am surprised
by the number of secondaries created by low energy neutrons as shown
below ... I suspect this is the cause of the stack overflow and I would
appreciate any comments from colleagues which are experienced with fixed
target experiments with protons.

 Number of secondaries created by low energy neutron per beam particle:

 Prompt radiation Radioactive decays

   1.8729E+05 (100.%) 0.0000E+00 (100.%)
   1.8545E+05 (99.0%) 0.0000E+00 ( 0.0%) NEUTRON
   2.7424E+02 ( 0.1%) 0.0000E+00 ( 0.0%) fission NEUTRON
   0.0000E+00 ( 0.0%) 0.0000E+00 ( 0.0%) PROTON
   1.5590E+03 ( 0.8%) 0.0000E+00 ( 0.0%) PHOTON

In general (I don t think this will solve your problem though), if you
are only interested by the neutron fluence (based on your USRBIN card
and not energy deposition) you could switch off the electromagnetic part
of the problem (EMF card) to reduce the number of secondaries in the
stack and decrease CPU time....

Joachim

________________________________

From: owner-fluka-discuss_at_mi.infn.it on behalf of
J.B.Benton_at_warwick.ac.uk
Sent: Wed 7/22/2009 5:59 PM
To: fluka-discuss_at_fluka.org
Subject: Stack Overflow Termination in fission experiment

Dear Fluka team,

I am new to fluka and while running a simulation i get the error message
"Stack overflow in Feeder. Execution terminated." I am unsure what this
means but i'm confident it is caused by my use of uranium 233 in a
low-mat
card. In this arrangement it is expected for the uranium to undergo
fission (sub-critically) and i encounter the same problem when
substituting for other fissionable materials (uranium 235, plutonium
etc.)
but not for regular materials such as uranium 238. Is this a limit of
the
code or can chain reactions be calculated successfully? I have attached
my
input file in case it is of use.

Thank you for your help.
Jack Benton
Received on Fri Jul 24 2009 - 09:31:41 CEST