Specifying temperatures in MCNP

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In summary, when expressing temperature in the cell cards of MCNP, you must specify it in units of MeV by multiplying the temperature in Kelvin by the Boltzmann constant. This is also needed in the material cards, where you must attach the library generated at the correct temperatures. The list of library identifiers and temperatures can be found in a separate document. If you need temperatures that do not line up with the library temperatures, you can use the "makxsf" utility program or wait for the development of "on-the-fly" temperatures in a future version of MCNP. It is recommended to change the title of the post to something related to specifying temperatures in MCNP, as it has nothing to do with supercritical water reactors.
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Aly_19f
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Temperature in MCNP
How do I express the temperature in the cell cards of the MCNP?, Say the temperature of the fuel is 500K, how do I write it as the following PWR example?
 

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In the cell cards, you specify the temperature in units of MeV by multiplying the temperature in Kelvin by the Boltzmann constant 8.617e-11 MeV/K. For example, 600K would be "tmp=5.17020E-08"

However, this is not the only place you need to worry about temperatures. In the material cards, you need to attach the library generated at the correct temperatures. A list of the library identifiers and temperatures used to be included in the "Appendix G" of the users manual, but it has now moved to a separate document. There may be a newer version, but I have report LA-UR-17-20709.
If you are using the ENDF/B-VII.1 cross sections, ".80c" is at 293.6 K, ".81c" is at 600 K, ".82c" is at 900 K, etc.

Finally, you also need to make sure you are using the correct temperature S(alpha,beta) cards. These can be found in Appendix G also.

If you need temperatures that do not line up with the library temperatures, there is a utility program "makxsf" that you can use to interpolate existing libraries and create libraries at user specified temperatures.

There is also development work to allow "on-the-fly" temperatures, but I am not sure what the status of this is. It will probably be released in a future version of MCNP.
 
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I also suggest that you change the name of the post to something that has to do with specifying temperatures in MCNP. Your question has nothing to do with supercritical water reactors.
 
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rpp said:
I also suggest that you change the name of the post to something that has to do with specifying temperatures in MCNP. Your question has nothing to do with supercritical water reactors.
@rpp -- Can you propose a new title? I think the edit window for the OP has expired, but the Mentors can change the title still...
 
  • #5
berkeman said:
@rpp -- Can you propose a new title? I think the edit window for the OP has expired, but the Mentors can change the title still...
How about "Specifying temperatures in MCNP"?
 
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Done. Thanks!
 
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rpp said:
How about "Specifying temperatures in MCNP"?
rpp said:
I also suggest that you change the name of the post to something that has to do with specifying temperatures in MCNP. Your question has nothing to do with supercritical water reactors.
I'm very thankful to you, and I apologize for the fatal mistake of the title but I couldn't edit it when I saw your reply two days ago.
 
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1. How do I specify temperatures in MCNP?

To specify temperatures in MCNP, you can use the T card. This card allows you to input temperatures for specific materials or regions in your model. You can also use the TEMP keyword in the SURF and CELL cards to assign temperatures to surfaces and cells.

2. Can I specify a temperature gradient in MCNP?

Yes, you can specify a temperature gradient in MCNP by using the TEMP GRAD keyword in the SURF and CELL cards. This allows you to define a linear or exponential temperature gradient within a specific region or material.

3. How are temperatures treated in MCNP calculations?

In MCNP, temperatures are used to calculate the thermal neutron scattering cross sections and thermal neutron production rates. Temperatures also affect the material density and can impact the neutron transport calculations. It is important to accurately specify temperatures in MCNP for accurate results.

4. Can I use temperature-dependent cross sections in MCNP?

Yes, MCNP allows you to use temperature-dependent cross sections by using the ACE library. This library contains pre-calculated cross sections for various materials at different temperatures. You can specify the desired temperature and material composition to use these temperature-dependent cross sections in your MCNP model.

5. How do I verify the temperature settings in my MCNP model?

You can verify the temperature settings in your MCNP model by using the PRINT card with the T keyword. This will print out the temperatures that have been assigned to materials and regions in your model. You can also use the TEMP keyword in the PRINT card to print out the temperature-dependent cross sections used in your calculations.

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