RTP TRIGA Reactor Kinetics Parameters from OpenMC

The current work uses Iterated Fission Probability (IFP) routine that was recently implemented in OpenMC to calculate reactor kinetics parameters. IFP is calculated from the product of the multiplication factors tracked across the L+1 generations of fission progenies. Since IFP is an excellent estimator of adjoint flux, it is able to calculate Λ_eff , β_eff and β_i of the reactor. OpenMC calculation of the reactor itself has k_eff = 1.01687 with an effective mean neutron generation time, Λ_eff = 44.82 μs. The effective delayed neutron fraction, β_eff that we get is 0.007235 or 723.5 pcm. Other calculations of β_eff using prompt methods for reactors with similar designs gave us values between 724 pcm to 752 pcm. Our own calculations using the prompt method in OpenMC gave us an effective delayed neutron fraction of 734.1 pcm. The group β_i that we obtain is 24 pcm, 131.4 pcm,124.1 pcm, 284.0 pcm, 112.7 pcm and 47.4 pcm respectively. If we strip away the influences of β_eff on β_i , by looking at only the abundances of each delayed neutron group, a_i ; we are able to see that the a_i is similar to the abundances of just ²³⁵U in the six group abundances of ENDF/B-VIII.0 evaluated cross section library. When we adopt a different evaluated cross section library in OpenMC, changes in β_i is due to the different β_eff and λ_i adopted in these libraries.