Question on CXs for tritium breeding with ORIGEN/COUPLE

[Martin Nieto]

I am using the ORIGEN/COUPLE modules of SCALE 6.2 to estimate tritium breeding on lithium oxide. I use COUPLE to generate a reaction library for a problem-specific 238-group neutron flux with energy bins compatible with the ORIGEN CX libraries. I searched for the 6Li(n, alpha)T cross-section on NDS IAEA database and I weight it with my flux energy distribution, getting a cross-section of 2.5 barns. The COUPLE output file reports, for the same flux energy structure, 5.64 barns. I checked with the reaction 3H(n,p)T to see if the source of discrepancy was somehow my COUPLE input. My manual calculation gives, for the same neutron flux structure, 10.9 barns, while the COUPLE output reports 11.62. Here is the relevant fragment of COUPLE Output, with the relevant cross-sections highlighted

20030 to  20040  1.43759E-05      mt= 102

20030 to  10030  1.16203E+01      mt= 103

20030 to  10010  1.35030E+02      mt= 103  byproduct

20030 to  10020  3.85550E-03      mt= 104

20030 tot-cap    1.16222E+01

30060 to  10010  2.13814E-03      mt=  24

30060 to  20040  2.39352E+00      mt=  32

30060 to  10020  3.94633E-02      mt=  32  byproduct

30060 to  30070  9.47261E-05      mt= 102

30060 to  20060  4.50613E-04      mt= 103

30060 to  10030  5.64228E+00      mt= 105  byproduct

30060 tot-cap    2.39407E+00

Any feedback will be greatly appreciated. Thank you.

[Steve Skutnik]

Hi Martin,

Could you provide some more info on your input? Specifically, are you able to provide the weighting spectrum you are using?

SCALE uses JEFF/3.0-A for light element reactions (like the ones you indicate above), but these are pretty linear over most of the range, so it seems like the data source shouldn't be a primary factor.

Also, I assume you mean He-3 (n,p); correct?

[Martin Nieto]

Here is a copy of my input file. A library file is generated first based on the neutron spectrum, and then irradiation is done for 10 days at constant flux, with intermediate decay steps.

[Will Wieselquist]

Hello Martin,

I used just the COUPLE part from your attached input focusing on the Li-6 mt=105. This is actually the Li-6 (n,t) reaction.  

30060 to  10030  5.64228E+00      mt= 105  byproduct

Our JEFF data shows this

We realized a problem with the COUPLE output for byproducts and fixed in SCALE 6.2.3 where at the time of the printout, not all byproduct data was fully resolved. This extended back to 6.1.3. We removed the byproduct output lines in 6.2.3. This output is "on-the-fly" COUPLE telling you what it is evaluating. We prefer the printout option "1$$ a14 1", e.g.

1$$ a2 0 a14 1 a15 -1 a16 8 a18 238 e t

for understanding the data that actually gets put on the library. This data is organized by daughter, so to check the byproduct (tritium=t) of the (n,t) reaction, see the highlighted value.

  h  3   10030  1.084E-03      h  2   10020 2.862E-06  he  3   20030 8.222E+00  li  6   30060 1.783E+00  li  7   30070 1.092E-02
                              be  9   40090 2.939E-04   b 10   50100 9.136E-03   b 11   50110 2.345E-04   c 13   60130 7.645E-05
                               n 14   70140 8.126E-04   n 15   70150 3.500E-04   o 17   80170 3.007E-05   o 18   80180 1.540E-08
                               f 19   90190 1.160E-03  ne 21  100210 2.472E-05  na 22  110220 5.352E-07  na 23  110230 6.561E-05

This compares well with a hand calculation using your spectrum with our JEFF 238 data plotted in Fulcrum and the exported to a spreadsheet.

I also ran the COUPLE cases with SCALE 6.1.3 and 6.2.0-6.2.3 to inspect the output (attached). There are no significant differences I saw except for the byproduct information output:

30060 to  10030  5.64228E+00      mt= 105  byproduct

which isn't there in 6.2.3 and later. 6.3.0 will include a pretty substantial modernization of COUPLE (available from within the "lib" block in ORIGEN) so we didn't want to put to much effort on tracking down why the byproduct information lines weren't correct--they are correct on the library and that is the important thing.

To close the loop, if you look at the "real" product of Li-6(n,t) = alpha, you'll see this.

 he  4   20040  0.000E+00     he  3   20030 1.609E-05  li  6   30060 1.804E+00  li  7   30070 1.126E-02  be  7   40070 3.457E-02
                              be  9   40090 3.108E-03  be 10   40100 2.589E-04   b 10   50100 6.367E+00   b 11   50110 6.811E-04
                               c 12   60120 1.472E-02   c 13   60130 2.015E-03   c 14   60140 1.258E-04   n 14   70140 9.605E-03

Why is the production of he4 from li6 1.804 barns but the production of tritium from li6 is only 1.783 barns? It turns out there is another reaction Li-6(n,n'd) which also produces an alpha (mt=32) and finally an n,2nalpha (mt=24) for completeness.

Finally, I noticed in your ORIGEN input you have lines like:

 lib {
   file = "${INPDIR}/cx.f33" pos=1
 }

ORIGEN actually does not know how to expand the ${INPDIR} environment variable. It is expecting a real file name. So you can just change this to:

 lib {
   file = "ft33f001" pos=1
 }

Best,

Will Wieselquist

SCALE Team