166
C. H. Pyeon
6.1.3 Discussion
6.1.3.1 Fission Reaction Rate Ratio
The region-wise contribution of energy was examined by MCNP6.1 and ENDF/BVII.1, for
237 Np and
241 Am fission reaction rates ratios to
235 U, with the use of reaction
rates normalized by summarizing entire reaction rates over the whole energy. For the
sake of comparison in Fig. 6.11, the energy distribution of
237 Np and
235 U fission
reaction rates are shown for the critical irradiation in the HEU-Pb zone shown in
Fig. 6.4a, demonstrating that
237 Np fission rate has high sensitivity to fission reactions
around a few MeV region as well as in the neutron spectrum of the HEU-Pb zone
shown in Fig. 6.5. Also,
235 U fission reactions were found to be dominant over the
thermal and epi-thermal neutron regions for critical irradiation in the HEU-Pb zone,
as shown in Fig. 6.11.
Fission reaction rates of
241 Am were acquired mainly in a few MeV region in
HEU-Pb and HEU-PE zones shown in Figs. 6.12 and 6.13, respectively, although
Fig. 6.11 Region-wise
contribution of energy of
237 Np and 235 U fission
reaction rates by MCNP
calculations in HEU-Pb zone
at critical state (Ref. [1])
10
-10
10
-9 10
-8 10
-7 10
-6 10
-5 10
-4 10
-3 10
-2 10
-1 10
0 10
1 10
2
0
0.02
0.04
0.06
0.08
0.10
0.12
Neutron energy [MeV]
Normalized fission reaction rate / lethargy
[Arbitray units]
235 U (10 g)
237 Np
235 U
237 Np
Fig. 6.12 Region-wise
contribution of energy of
241 Am and 235 U fission
reaction rates by MCNP
calculations in HEU-Pb zone
at critical state (Ref. [1])
10
-10
10
-9 10
-8 10
-7 10
-6 10
-5 10
-4 10
-3 10
-2 10
-1 10
0 10
1 10
2
0
0.02
0.04
0.06
0.08
0.10
0.12
235 U (5 g)
241 Am
235 U
241 Am
Neutron energy [MeV]
Normalized fission reaction rate / lethargy
[Arbitrary units]