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Engineering
Nuclear Engineering
MCNP FMESH for Plotting power distribution
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[QUOTE="Grelbr42, post: 6860929, member: 732225"] Some generic comments first. I notice you have a code with 10000 per cycle, 50 skipped cycles, and 200 cycles total. It is unlikely you will have good convergence. Check carefully what is happening in the output to see if you are getting good stats. You might want to increase the particle per cycle to 1E5 or even more. And you might want to increase the skipped cycles and total cycles as well. Do some testing and check the results for convergence. MCNP reports a variety of things to guide you about the stats. For FMESH, you will want to read carefully in the manual about using reflective surfaces. Your surfaces 500 and 501 are reflective. You can do it, you just need to be careful about normalization and such. You will also want to be reading carefully in the manual about setting up your FMESH. It imposes a tally on top of the model. You set up a grid in x-y-z that does not depend on the cell boundaries. Basically, you specify to the FMESH card the origin of your mesh, the x-axis of the mesh, and the intervals to mesh over in each of x, y, and z. By default, FMESH is going to give you the neutron flux in each mesh region. The normalization is going to be "per particle started." You can do neutrons or photons. You can add multipliers to produce various things. For example, you can use a multiplier that is the cross section for various interactions such that you get things like neutron capture, neutron scattering, and so on. You can then get the heat deposited in each grid. This will produce something like MeV per neutron started. To use this in CFD you are going to need to normalize it to give power, that is, energy per second. That means you will need the number of neutrons per second. Your reactor may provide you with this information. Or you may need to calculate it. For example: Suppose your reactor is operating at 1 kilo-Watt (1 kW). Then you need to work out the average energy per fission, typically in the range of 200 MeV, depending on design. You can get MCNP to work that out for you for a kcode calculation, check the manual. There are some steps involved. So you divide 1 kW by 200 MeV, convert the units, and it gives you neutrons per second. Keep in mind that's for the full core and you modeled 1/12. You multiply the value the FMESH gave you by the number of neutrons per second, and it converts it to a value per-second. [/QUOTE]
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MCNP FMESH for Plotting power distribution
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