DPA calculation: damage-energy score

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1

Hi everyone,
I have a doubt on the damage-energy (MT=444) score tally units for dpa calculation. The quantity we should obtain tallying the damage energy, calculated by NJOY, is the damage energy production in units of [eV-barn] but the documentation says we should get directly something in units of eV. Can somebody clarify on this?
Thank you.
Lorenzo

2

Hi @lorenzo,

You are correct that the information from NJOY for damage energy is given in units of [eV-b]. This is the microscopic cross section value for damage energy of an isotope. Once multiplied by the number densities of a material, we can use the resulting macroscopic cross section (in units of [eV / cm]) to produce a reaction rate in units of [eV / source-particle].

You can see a similar situation for heating in the theory section. of the OpenMC documentation.

I hope this helps.

-Patrick

3

Hi @pshriwise;
Thank you for the prompt answer. If I got right, from NJOY we get [eV-barn] but from the damage-energy tally we get [eV-source]. The conversion is done by the tally itself, is that correct?
Lorenzo

4

Hi @lorenzo, correct. The conversion of these units happens during the simulation itself.

1 Like
6

Hi Patrick,

Sorry to revive this old thread but does this mean that for a DPA calculation but localized in a mesh tally mean that i can take the damage-energy tally in [eV-source] and multiply by source rate [neutrons-sec] to get E_d in the NRT-DPA equation? If this is the case the NRT-DPA equation will give me [displacements-s] so I would need to divide by the total number of atoms in that mesh cell. I can use atomic density [atoms-cm3] and volume of cell element [cm3] to find total number of atoms then that will give me [DPA/s] for that localized mesh element correct?

Also is there a way to get the damage cross sections?

This is a question because I am currently working of 3 dimensional neutronic simulations of fusion reactors and trying to have a mapping of the dpa however the results I am currently getting are orders of magnitude larger than what I am expecting.

Thanks,
Travis

7

Hi @thallam,

Based on the following equation for NRT-DPA

dpa = \frac{0.8 T_d}{2 E_d}

what the damage-energy score in OpenMC will provide is the total energy that causes material damage in eV (T_d in the equation above). From that point on your evaluation of the units and normalization is correct yes. And yes to get displacements per atom you’ll need to divide by the number of atoms in the volume associated with that tally bin (mesh element, cell, material, etc.).

The damage cross sections are provided to OpenMC by NJOY’s HEATR module and can be accessed/plotted like any other cross section in OpenMC yep.

image

Hope this helps.

-Patrick

8

Example for DPA might be useful neutronics-workshop/tasks/task_06_CSG_cell_tally_DPA at d8337142623ffe812b8c8e0470695661857db86a · fusion-energy/neutronics-workshop · GitHub

9

Thank you both,

Turns out my entire calculations were correct except when calculating the atomic densities of my material I was multiplying by a fraction in percent form rather than decimal form. This caused my final dpa calculations to be 2 magnitudes to large.

I am currently working on a workflow to utilize OpenMC to produce high fidelity 3D maps of fusion reactors to analyze different neutronics based parameters. I have written a couple of functions to open the .h5m file and my exodus file to extract the materials and block information. I have written these functions to hopefully handle any geometry given to it to post process tally data in the unstructured mesh easier. So with this I’m able to calculate the dpa in each cell in the volumetric mesh and display in a high fidelity 3D visualization.