Neutron energy spectrum

dawn · November 27, 2024, 3:06pm

hello，I could use Openmc to tally ‌ the neutron flux spectrum，but how can I tally the neutron spectrum？

Shimwell · December 6, 2024, 2:16pm

I have some examples here that tally neutron spectrum on cells and surfaces

The key thing that is needed is an openmc.EnergyFilter()

dawn · January 4, 2025, 1:53pm

Dear Shimwell：First of all, thank you for your response. I apologize if I wasn’t clear. What I meant was that I would like to know the energy distribution of neutrons, so that I can calculate the average neutron energy.

Shimwell · January 4, 2025, 4:53pm

Ah sorry for misunderstanding.

But good news is I have an example for energy distribution of neutrons as well.

github.com/fusion-energy/neutronics-workshop

plotting neutron angle energy

opened 03:16PM - 01 Aug 23 UTC

shimwell

we could add an energy angle plot for the nuclear data section ```python # T…his example plots the probability of scattering angle for different incident neutron energies. import openmc import matplotlib.pyplot as plt from pprint import pprint import math nuc_path = "/home/jshimwell/ENDF-B-VIII.0-NNDC/h5_files/neutron/C12.h5" # /nuclear_data/ENDFB-8.0-NNDC_Au197.h5 gold = openmc.data.IncidentNeutron.from_hdf5(nuc_path) print(list(gold.reactions.values())) gold_elastic = gold[2] print(gold_elastic.products) neutron_out = gold_elastic.products[0] dist = neutron_out.distribution[0] pprint(list(gold.reactions.values())) fig, ax = plt.subplots() neutron_energy = dist.angle.energy # This loops through the incident neutron energies and the angular distributions # This loop also uses some python list slicing syntax # As the nuclear data goes to high energies (150MeV) we skip the last 15 entries of the list with the [:-15] part # As there are a lot of data points for lots of energies we are plotting every 50th neutron energy with [:::50] part for energy, angle in zip(dist.angle.energy[:-15][::50], dist.angle.mu[:-15][::50]): ax.plot(angle.x, angle.p, label=f"neutron energy={energy/1e6}MeV") import numpy as np def forward(x): vals = [] for v in x: vals.append(math.cos(v)) # return vals return np.array(vals) def inverse(x): vals = [] for v in x: vals.append(math.acos(v)) return np.array(vals) # (lambda x: math.degrees(math.acos(x)), lambda x: math.cos(math.radians(x)) secax = ax.secondary_xaxis('top', functions=(forward, inverse)) secax.set_xlabel('angle [degrees]') # plt.xlabel("scattering cosines") # plt.ylabel("probability") # plt.title("Neutron energy angle distribution of C12") # plt.legend(bbox_to_anchor=(1.01, 0.9)) # plt.tight_layout() plt.show()#savefig("angle_energy_c12.png", bbox_inches="tight", dpi=400) ```

dawn · January 4, 2025, 11:51pm

Dear Shimwell：Thank you once again for your response. The example you provided is excellent. I apologize for not being clear enough. As we know, in pressurized water reactors, due to the presence of moderators, neutrons are primarily thermal neutrons. In metal nuclear reactors, there is no moderator, so the neutron energy is higher. Therefore, I would like to compare the average neutron energy in these two types of reactor cores.I can only use OpenMC to calculate the flux distribution in different energy bins, but how can I obtain the average neutron energy for different reactor cores?

Shimwell · January 25, 2025, 9:17pm

You would need a model of each core. Run aaa simulation for each model and compare the results.

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Neutron energy spectrum

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