helo, I have simulated htr-10 with openmc. but I’m a little confused by the results. why does the neutron flux decrease when the number of pebble beds increases. Is this true?
when the number of pebble bed (fuel) increase from 16000 to 27000 in reactoe core, the flux in the same position decrease.
Hi Inagena, welcome back to the community.
I think it’s quite obvious that the neutron flux will decrease when you add identical fuel to the core with the same amount of thermal power.
We knew that our core thermal power would be equal to power/fission × SigFission × flux × core volume. Sorry for the oversimplification, but if you add the fuel, then your core volume will increase. To get the same core power, we will only need a smaller amount of neutron flux.
If you add another type of fuel, maybe you add a fueled pebble that contains a lot of fertile material, i.e. natural uranium or thorium, then the neutron flux could be increased since the fission reaction rate will change caused by the addition of fertile material, so the SigFission will be decreased. Then you will need more neutron flux to achieve a similar amount of core thermal power.
You can also check this out by changing the fissile loading of your pebble. If you use a higher fissile loading, then the neutron flux will be decreased because the fission reaction cross section increased, making the same amount of fission rate can be achieved with a lower neutron flux.
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