Reaction rate vs Burnup.

General information etc.
Post Reply
Osama
Posts: 4
Joined: Thu Aug 30, 2018 5:17 pm
Security question 1: No
Security question 2: 93

Reaction rate vs Burnup.

Post by Osama » Sat Sep 05, 2020 7:29 pm

Dear all,

I have some questions, please:

1. When using

Code: Select all

det Totalflux dm Am
should I divide the result on the volume of Am material to get the total neutron flux in Am material integrated over space and energy (from 0 to infinity)?

2. To calculate the total microscopic reaction rate of Am-241 in the Am material I set the following detector setup:

Code: Select all

mat Am241 1.0 95241.09c 1.0
det TotalRR dm Am dr 1  Am241 


Here also should I divide the result on the volume of Am material? Is the result multiplied by the Am-241 atomic density? If yes, why the reaction rate of Am-241 is increasing with burnup? please see the Figs. below.

3. I use

Code: Select all

det TotalXS dm Am dr 1  Am241 dt 3 Totalflux
to calculate the total microscopic cross sections of Am-241 in the Am material. Is this the best way to do that? and the unit will be in [barn]?

Thanks in advance
Last edited by Osama on Sat Sep 05, 2020 7:32 pm, edited 1 time in total.

Osama
Posts: 4
Joined: Thu Aug 30, 2018 5:17 pm
Security question 1: No
Security question 2: 93

Re: Reaction rate vs Burnup.

Post by Osama » Sat Sep 05, 2020 7:31 pm

i
Attachments
OS_3.png
OS_3.png (7.44 KiB) Viewed 599 times
OS_2.png
OS_2.png (9.91 KiB) Viewed 599 times
Os_1.png
Os_1.png (8.25 KiB) Viewed 599 times

User avatar
Jaakko Leppänen
Site Admin
Posts: 2388
Joined: Thu Mar 18, 2010 10:43 pm
Security question 2: 0
Location: Espoo, Finland
Contact:

Re: Reaction rate vs Burnup.

Post by Jaakko Leppänen » Sun Sep 06, 2020 10:26 am

All cell flux detectors are integrated over volume, so the flux detector gives you the integral flux, reaction rate detector the integral reaction rate. So if you want your flux to be in units n/cm²s, you need to divide by volume, etc. For the calculation of microscopic cross sections this is not necessary, because you are calculating the ratio of two integral terms.

Also note that microscopic reaction rate is sometimes expressed in terms of reactions per atom, in which case you need to change the divider.
- Jaakko

Osama
Posts: 4
Joined: Thu Aug 30, 2018 5:17 pm
Security question 1: No
Security question 2: 93

Re: Reaction rate vs Burnup.

Post by Osama » Sun Sep 06, 2020 11:29 am

Dear Jaakko Leppänen,
Thank you for your reply.

Why we set the density to unity here?

Code: Select all

mat Am241 1.0 95241.09c 1.0
Is the response function

Code: Select all

dr 1 
means σ total [barn] * rho [atom/barn.cm]?
Also note that microscopic reaction rate is sometimes expressed in terms of reactions per atom, in which case you need to change the divider.
Did you mean reaction per sec, if yes, what will be the divider in this case?

Thanks

Ana Jambrina
Posts: 113
Joined: Tue May 26, 2020 5:32 pm
Security question 1: No
Security question 2: 7

Re: Reaction rate vs Burnup.

Post by Ana Jambrina » Sun Sep 06, 2020 1:05 pm

The ENDF reaction MT numbers are universal and related to isotopic cross sections. These reactions may not be used with materials consisting of more than one nuclide. The result is multiplied by the material atomic density and microscopic reaction rates can be calculated by setting the density to unity. (For further details: http://montecarlo.vtt.fi/download/Serpent_manual.pdf, section 7.1).

Check Serpent standard units for clarification: http://serpent.vtt.fi/mediawiki/index.p ... _constants.
- Ana

User avatar
Jaakko Leppänen
Site Admin
Posts: 2388
Joined: Thu Mar 18, 2010 10:43 pm
Security question 2: 0
Location: Espoo, Finland
Contact:

Re: Reaction rate vs Burnup.

Post by Jaakko Leppänen » Sun Sep 06, 2020 2:00 pm

To be precise, material density is used as a multiplier only for macroscopic reaction rates (negative response numbers). For microscopic rates the density in the material card plays no role.
- Jaakko

Osama
Posts: 4
Joined: Thu Aug 30, 2018 5:17 pm
Security question 1: No
Security question 2: 93

Re: Reaction rate vs Burnup.

Post by Osama » Mon Sep 07, 2020 1:04 am

Thank you for your reply.

Does anyone can explain this:

The input is

Code: Select all

det Totalflux dm Am
mat Am241 1.0 95241.09c 1.0
det TotalRR dm Am dr 1  Am241  
det TotalXS dm Am dr 1  Am241 dt 3 Totalflux
the output is

DETTotalflux = [
1 1 1 1 1 1 1 1 1 1 1.09991E+17 0.02933
];
DETTotalRR = [
1 1 1 1 1 1 1 1 1 1 2.37857E+18 0.02049
];
DETTotalXS = [
1 1 1 1 1 1 1 1 1 1 2.88750E+02 0.03870
];

Why DETTotalRR/DETTotalflux NOT equal the DETTotalXS ??
The volume of the Am material (cylinder) is 83.333 cm3.

User avatar
Jaakko Leppänen
Site Admin
Posts: 2388
Joined: Thu Mar 18, 2010 10:43 pm
Security question 2: 0
Location: Espoo, Finland
Contact:

Re: Reaction rate vs Burnup.

Post by Jaakko Leppänen » Mon Sep 07, 2020 8:34 am

Can you post the full input or send it o me by email?
- Jaakko

User avatar
Jaakko Leppänen
Site Admin
Posts: 2388
Joined: Thu Mar 18, 2010 10:43 pm
Security question 2: 0
Location: Espoo, Finland
Contact:

Re: Reaction rate vs Burnup.

Post by Jaakko Leppänen » Mon Sep 07, 2020 12:26 pm

My guess is, that there is some geometry error, possibly an overlap, related to material Am. If you replace "dm Am" with another material (e.g. "dm graphite") the results are consistent (TotalXS gives the same result as TotalRR/Totalflux).
- Jaakko

Post Reply