4 Factor formula parameters

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Four factors formula

Hi Paul and Adam, Happy new year 2014. Out of curiosity, I wanted to reproduce the value of K_infinity from reaction rate tallies. I adopted the indc-usa-107 problem 1 from benchmarks-master examples. Results: (see attached files) The four factors formula underestimates K_infinity. While comparing to results of MCNP, I found that the reproduction factor η is strongly underestimated by OpenMC even if the results for ν Σ f are the same for both the two codes. Whereas the thermal utilization fa…