Model Fuel Assembly w/ Gamma Source: Solving a Sampling Problem

[Gregorovych]

Hi everyone, I'm making a fuel assembly model and I would like to have a cylindrical gamma source on each fuel rod to measure the decay heat of a fuel assembly but I'm struggling to define the source since it is in a repeated structure. This is the geometry of my model:
Level 2 : cells 1, 2 3 and 4 corresponding to a fuel pin and is defined by universe 1
Level 1 : cell 5 which is a lattice made of universe 1 and universe 3 (filled by himself +universe 1) like this: lat=1 fill=-14:0 -14:0 0:0 11111111111
11131131111u=3
Level 0 : cell 6 filled by universe 3 and cell 7 defines the outside world

Then, I defined my source by giving an discrete energy distribution (corresponding to the highest gamma peaks), the cell definition and finally the axial and radial sampling limits (corresponding to the dimensions of the fuel rod):
SDEF ERG=D1 CEL=D3:D4 RAD=D5 EXT=D6 PAR=P (I will put only the cell def for clarity)

SI3 L (4<5[u=1]<6)
SP3 1 1 1 1 1 1... (# corresponding to all fuel rods)
SI4 L 1 2 3
SP3 1 0 0

When I'm running my code, the following message appears:
" entry 3 on SI -1141636198 for independent variable cel at the last sampled position 1.20045E-01 1.24405E-02 -2.41423E-01 appears incorrect. Expire parameter is the sampling efficiency in source cell 1 is too low. bad trouble in subroutine sourcb of mcrun source particle no. 1 starting random number = 6647299061401 the sampling efficiency in source cell 1 is too low. "

I understand that there is a problem at the beginning of the simulation when the program tries to sample the particles, but I don't know how to solve this problem. I already tried to use the lower the EFF parameter when defining my source but it is only taking more time to write me the same message. I think that the problem can come from the source path because I didn't completely understood how to define the source path.

Any and all info/suggestions would be gratefully received! Thank you in advance for your response!

 

[Alex A]

Your lattice should be 15 lines of 15 entries, and I see 2 lines of 11 entries, you have two SP3 cards, I'm guessing the second one should be an SP4 card? If you can't share your input file, can you cut it down until you have something you can share that produces the same error?

There are concepts here I don't understand, like lattices filled with themselves. I've dipped into the manual and the only mention of Sampling efficiency is a screaming nightmare.

 

[Gregorovych]

Here is my input file with the same error. I looked at the manual and I really don't know how the sampling efficiency is importamt for the simulation. Thank you for your help!

C ------------------- Cell cards ----------------------
c
c ********************Fuel rod ************************
c
1 1 -10.97 -1 u=1
2 2 -0.1785 1 -2 u=1
3 3 -6.49 2 -3 u=1
4 4 -1 3 u=1
c
c ******************** Location of water rods **************
c
5 4 -1 110 -120 130 -140 lat=1 fill=-14:0 -14:0 0:0
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 3 1 1 3 1 1 1 3 1 1 3 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 3 1 1 3 1 1 3 1 1 1 1
1 1 3 1 1 1 1 1 1 1 1 1 3 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 3 1 1 1 1 1 3 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 3 1 1 1 1 1 1 1 1 1 3 1 1
1 1 1 1 3 1 1 3 1 1 3 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 3 1 1 3 1 1 1 3 1 1 3 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 u=3
c
c ******************** Assembly ************************
c
6 4 -1 -100 fill=3
7 4 -1 100 -170
8 0 170

C ------------------- Surface cards ----------------------
c
c ********************** Fuel rod ************************
c
1 RCC -10.01 -10.01 -159.5 0 0 319 0.46
2 RCC -10.01 -10.01 -159.5 0 0 319 0.475
3 RCC -10.01 -10.01 -159.5 0 0 319 0.525
c
c ********************** Box (assembly) **********************
c
100 RPP -10.725 10.725 -10.725 10.725 -159.6 159.6
c
c ********************** Lattice for box-assembly **********************
c
110 px -10.725
120 px -9.295
130 py -10.725
140 py -9.295
c
c
170 RPP -11 11 -11 11 -170 170
c

C ------------------- Data cards ----------------------
c -------------------- Source -------------------------
Mode P
NPS 1000
IMP:P 1 1 1 1 1 1 1 0
SDEF CEL=D2:D3 RAD=D5 EXT=D6 PAR=P
c
c *********************** Cell definition ***********************
c
SI2 L (4<5[u=1]<6)
SP2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
c
SI3 L 1 2 3
SP3 1 1 1
c
c *********************** Radial sampling limits ***********************
c
SI5 0 0.46
SP5 -21 2
c
c *********************** Axial sampling limits ***********************
c
SI6 -159.5 159.5
SP6 -21 0
c
c ------------------------ Materials -------------------------
c
c *********************** Uranium oxide ***********************
c
M1 92238 -0.837425 $ fresh fuel : 88.15% uranium and 11.85 % oxygen
92235 -0.044075
8016 -0.1185
c
c *********************** Helium gap ***********************
c
M2 2004 1
c
c *********************** Zirconium alloy***********************
c
M3 40090 -0.5145
40091 -0.1122
40092 -0.1715
40094 -0.1738
40096 -0.028
c
c *********************** Water (demineralised) ***********************
c
M4 1001 -0.66667
8016 -0.33333

 

[Alex A]

Hi,

This forum messes up formatting, and that can cause things to fail. This is fairly short and I've tried to fix them but I'm getting errors that will not go away. Could you rename your input file to add .txt at the end and then attach to a post please.

Edit, please still do that, but I note that when the version I've corrected is run in mcnp 5.1.6 or 6.1 they segfault, in mcnpx the error is the same as your error.

 

[anorlunda]

This forum messes up formatting

Use [CODE] [/CODE] tags.

For example, without CODE tags,
c ********************Fuel rod ************************
c
1 1 -10.97 -1 u=1
2 2 -0.1785 1 -2 u=1
3 3 -6.49 2 -3 u=1
4 4 -1 3 u=1

and with CODE tags.

c ********************Fuel rod ************************
c
1 1 -10.97 -1 u=1
2 2 -0.1785 1 -2 u=1
3 3 -6.49 2 -3 u=1
4 4 -1 3 u=1

 

[Gregorovych]

Thank you for your response. I have attached the input file (txt format) with the correct syntax + I used the code tags:
[CODE title="MCNP code"]
C ------------------- Cell cards ----------------------
c
c ********************Fuel rod ************************
c
1 1 -10.97 -1 u=1
2 2 -0.1785 1 -2 u=1
3 3 -6.49 2 -3 u=1
4 4 -1 3 u=1
c
c ******************** Location of water rods **************
c
5 4 -1 110 -120 130 -140 lat=1 fill=-14:0 -14:0 0:0
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 3 1 1 3 1 1 1 3 1 1 3 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 3 1 1 3 1 1 3 1 1 1 1
1 1 3 1 1 1 1 1 1 1 1 1 3 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 3 1 1 1 1 1 3 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 3 1 1 1 1 1 1 1 1 1 3 1 1
1 1 1 1 3 1 1 3 1 1 3 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 3 1 1 3 1 1 1 3 1 1 3 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 u=3
c
c ******************** Assembly ************************
c
6 4 -1 -100 fill=3
7 4 -1 100 -170
8 0 170

C ------------------- Surface cards ----------------------
c
c ********************** Fuel rod ************************
c
1 RCC -10.01 -10.01 -159.5 0 0 319 0.46
2 RCC -10.01 -10.01 -159.5 0 0 319 0.475
3 RCC -10.01 -10.01 -159.5 0 0 319 0.525
c
c ********************** Box (assembly) **********************
c
100 RPP -10.725 10.725 -10.725 10.725 -159.6 159.6
c
c ********************** Lattice for box-assembly **********************
c
110 px -10.725
120 px -9.295
130 py -10.725
140 py -9.295
c
c
170 RPP -11 11 -11 11 -170 170
c

C ------------------- Data cards ----------------------
c -------------------- Source -------------------------
Mode P
NPS 1000
IMP:P 1 1 1 1 1 1 1 0
SDEF CEL=D2:D3 RAD=D5 EXT=D6 PAR=P
c
c *********************** Cell definition ***********************
c
SI2 L (4<5[u=1]<6)
SP2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
c
SI3 L 1 2 3
SP3 1 1 1
c
c *********************** Radial sampling limits ***********************
c
SI5 0 0.46
SP5 -21 2
c
c *********************** Axial sampling limits ***********************
c
SI6 -159.5 159.5
SP6 -21 0
c
c ------------------------ Materials -------------------------
c
c *********************** Uranium oxide ***********************
c
M1 92238 -0.837425 $ fresh fuel : 88.15% uranium and 11.85 % oxygen
92235 -0.044075
8016 -0.1185
c
c *********************** Helium gap ***********************
c
M2 2004 1
c
c *********************** Zirconium alloy***********************
c
M3 40090 -0.5145
40091 -0.1122
40092 -0.1715
40094 -0.1738
40096 -0.028
c
c *********************** Water (demineralised) ***********************
c
M4 1001 -0.66667
8016 -0.33333[/CODE]

 

[Gregorovych]

Hello everyone,
I have found my problem :
So the basis of my cylinder is in x=-10.01 y=-10.01.
When I used the fact that POS=0 0 0, it has set the basis to x=0 y=0 z=0.
The code tries to find cell 1 (cause it is told to look for cell 1 on the CEL=d2 card) with the geometric data I
provide on the SDEF card: POS=0 0 0 RAD=D2 EXT=D3.

But it won't work out, cause cell 1 is defined with RCC, which basis is not on 0 0 0, as on the SDEF card. This is the cause of the error. The correct definition of my source is then:
[CODE title="MCNP:"]SDEF CEL=D1 POS=-10.01 -10.01 0 RAD=D2 EXT=D3 AXS=0 0 1 PAR=2
c
c *********************** Cell definition ***********************
c
SI1 L (1<5[u=1]<6)
SP1 D 1 204R
c
c *********************** Radial sampling limits ***********************
c
SI2 H 0 0.46
SP2 D -21 1
c
c *********************** Axial sampling limits ***********************
c
SI3 H -159.5 159.5
SP3 D 0 1[/CODE]

Thank you for your time!

 

[Alex A]

Ok, I made the following changes to make the input file work in linux,
Stripped windows line endings, this may not have been needed,
SI2 line exceeded 80 char limit, so I replaced that whole block with "SI2 1",
Removed tabs that X complained about, 5.1.6 and 6.1 were fine with them.

This produced a file that roughly generated your errors.

I'm out of my depth with your source description but the part that jumped out at me after a lot of messing was "CEL=D2:D3". It seems to me that you are trying to do an intersection between two distributions. When I changed that to just D2 all the weirdness went.

Cool you have it working now!