the neutron spectrum in eigenvalue mode is singular. In addition to this, the neutron
spectrum at the fuel region evaluated in eigenvalue mode is almost the same among
different subcritical states, because there is no change in fuel composition through
the experiment. Neutron spectrum at the fuel region evaluated in time-dependent
mode changes as a function of elapsed time after the injection of D-T neutrons, but
the shape of the spectrum becomes stable after around 1e
À4 s, although the
1E-4
1E-3
1E-2
1E-1
1E+0
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
Neutron flux [arb. unit]
distance from T-target [cm]
Fast (>100keV)
Thermal (<4eV)
Fig. 13.2 Neutron flux distribution evaluated in eigenvalue mode (13 fuel rods)
1E-3
1E-2
1E-1
1E+0
1E+1
1E+2
1E+3
1E+4
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
Neutron flux [arb. unit]
Distance from T-target [cm]
1e-6 [sec]
1e-5 [sec]
1e-4 [sec]
1e-3 [sec]
2e-3 [sec]
3e-3 [sec]
Fuel Region
Reflector Region
Reflector Region
Fig. 13.3 Neutron flux distribution evaluated in time-dependent mode (fast energy range, 13 fuel
rods)
132
T. Kitada et al.