118
M. Yamanaka
because of the slight difference in the number of fuel plates: 3016 and 3008. Also, in
terms of ENDF/B-VII.1, the three kinetics parameters were almost the same in the
two states.
At the subcritical state with 3000 fuel plates, three kinetics parameters showed
a meaningful change from the critical state, although the subcriticality was very
small and around the criticality (Table 4.22). Kinetic parameters α and ρ $ were
then obtained by the extended area ratio method and the least-square fitting method,
respectively, by varying the external neutron source: 14 MeV neutrons (Table 4.23)
and spallation neutrons (Table 4.24). Also, as shown in Tables 4.23 and 4.24, detector
position dependency was revealed interestingly: the results of Fiber #1 and BF-3 #3
were rather good, and on the contrary, those of Fiber #2, BF-3 #1, and BF-3 #3 looked
problematic.
Table 4.23 Measured prompt neutron decay constants α [s −1 ] deduced by least-square fitting
method, subcriticality ρ $ [$] (dollar units) by extended area ratio method, and β eff / [s −1 ] by
α-fitting method (# of HEU plates: 3000; subcritical core with 14 MeV neutrons in Fig. A4.3a)
(Ref. [23])
Detector
α [s −1 ]
ρ $ [$]
(β eff Λ)
exp [s −1 ]
C/E
BF-3 #1
294.78 ± 29.27
0.0228 ± 0.0070
288.20 ± 93.30
0.88 ± 0.29
BF-3 #2
226.96 ± 23.31
0.0158 ± 0.0054
223.44 ± 79.47
1.14 ± 0.41
BF-3 #3
258.58 ± 12.34
0.0194 ± 0.0027
253.66 ± 37.32
1.00 ± 0.15
Fiber #1
248.38 ± 39.04
0.0207 ± 0.0056
243.36 ± 72.07
1.04 ± 0.31
Fiber #2
229.95 ± 14.51
0.0200 ± 0.0032
225.45 ± 38.73
1.13 ± 0.19
Fiber #3
273.99 ± 26.24
0.0261 ± 0.0056
267.02 ± 62.56
0.95 ± 0.22
MCNP6.1 with JENDL-4.0: β eff = 806 ± 10 [pcm], = 31.71 ± 0.07 [μs], (β eff /Λ)
cal
J40 (MCNP6.1)
= 254.05 ± 3.07 [s -1 ]; C/E = (β eff /Λ)
cal
J40 / (β eff /Λ)
exp
Table 4.24 Measured prompt neutron decay constants α [s −1 ] deduced by least-square fitting
method, subcriticality ρ $ [$] (dollar units) by extended area ratio method, and β eff / [s −1 ] by
α-fitting method (# of HEU plates: 3000; subcritical core with spallation neutrons in Fig. A4.6a)
(Ref. [23])
Detector
α [s −1 ]
ρ $ [$]
(β eff /Λ)
exp [s −1 ]
C/E
BF-3 #1
276.25 ± 7.17
0.0900 ± 0.0011
253.43 ± 7.25
1.00 ± 0.03
BF-3 #2
300.62 ± 7.03
0.0966 ± 0.0011
274.13 ± 7.15
0.93 ± 0.03
BF-3 #3
259.96 ± 6.00
0.0899 ± 0.0011
238.53 ± 6.18
1.07 ± 0.03
Fiber #1
283.79 ± 15.38
0.0973 ± 0.0025
258.62 ± 15.49
0.98 ± 0.06
Fiber #2
360.05 ± 64.85
0.1139 ± 0.0087
323.24 ± 63.19
0.79 ± 0.15
Fiber #3
269.83 ± 26.36
0.1392 ± 0.0039
236.85 ± 24.04
1.07 ± 0.11
MCNP6.1 with JENDL-4.0: β eff = 806 ± 10 [pcm], = 31.71 ± 0.07 [μs], (β eff /Λ)
cal
J40 (MCNP6.1)
= 254.05 ± 3.07 [s -1 ]; C/E = (β eff /Λ)
cal
J40 / (β eff /Λ)
exp
M. Yamanaka
because of the slight difference in the number of fuel plates: 3016 and 3008. Also, in
terms of ENDF/B-VII.1, the three kinetics parameters were almost the same in the
two states.
At the subcritical state with 3000 fuel plates, three kinetics parameters showed
a meaningful change from the critical state, although the subcriticality was very
small and around the criticality (Table 4.22). Kinetic parameters α and ρ $ were
then obtained by the extended area ratio method and the least-square fitting method,
respectively, by varying the external neutron source: 14 MeV neutrons (Table 4.23)
and spallation neutrons (Table 4.24). Also, as shown in Tables 4.23 and 4.24, detector
position dependency was revealed interestingly: the results of Fiber #1 and BF-3 #3
were rather good, and on the contrary, those of Fiber #2, BF-3 #1, and BF-3 #3 looked
problematic.
Table 4.23 Measured prompt neutron decay constants α [s −1 ] deduced by least-square fitting
method, subcriticality ρ $ [$] (dollar units) by extended area ratio method, and β eff / [s −1 ] by
α-fitting method (# of HEU plates: 3000; subcritical core with 14 MeV neutrons in Fig. A4.3a)
(Ref. [23])
Detector
α [s −1 ]
ρ $ [$]
(β eff Λ)
exp [s −1 ]
C/E
BF-3 #1
294.78 ± 29.27
0.0228 ± 0.0070
288.20 ± 93.30
0.88 ± 0.29
BF-3 #2
226.96 ± 23.31
0.0158 ± 0.0054
223.44 ± 79.47
1.14 ± 0.41
BF-3 #3
258.58 ± 12.34
0.0194 ± 0.0027
253.66 ± 37.32
1.00 ± 0.15
Fiber #1
248.38 ± 39.04
0.0207 ± 0.0056
243.36 ± 72.07
1.04 ± 0.31
Fiber #2
229.95 ± 14.51
0.0200 ± 0.0032
225.45 ± 38.73
1.13 ± 0.19
Fiber #3
273.99 ± 26.24
0.0261 ± 0.0056
267.02 ± 62.56
0.95 ± 0.22
MCNP6.1 with JENDL-4.0: β eff = 806 ± 10 [pcm], = 31.71 ± 0.07 [μs], (β eff /Λ)
cal
J40 (MCNP6.1)
= 254.05 ± 3.07 [s -1 ]; C/E = (β eff /Λ)
cal
J40 / (β eff /Λ)
exp
Table 4.24 Measured prompt neutron decay constants α [s −1 ] deduced by least-square fitting
method, subcriticality ρ $ [$] (dollar units) by extended area ratio method, and β eff / [s −1 ] by
α-fitting method (# of HEU plates: 3000; subcritical core with spallation neutrons in Fig. A4.6a)
(Ref. [23])
Detector
α [s −1 ]
ρ $ [$]
(β eff /Λ)
exp [s −1 ]
C/E
BF-3 #1
276.25 ± 7.17
0.0900 ± 0.0011
253.43 ± 7.25
1.00 ± 0.03
BF-3 #2
300.62 ± 7.03
0.0966 ± 0.0011
274.13 ± 7.15
0.93 ± 0.03
BF-3 #3
259.96 ± 6.00
0.0899 ± 0.0011
238.53 ± 6.18
1.07 ± 0.03
Fiber #1
283.79 ± 15.38
0.0973 ± 0.0025
258.62 ± 15.49
0.98 ± 0.06
Fiber #2
360.05 ± 64.85
0.1139 ± 0.0087
323.24 ± 63.19
0.79 ± 0.15
Fiber #3
269.83 ± 26.36
0.1392 ± 0.0039
236.85 ± 24.04
1.07 ± 0.11
MCNP6.1 with JENDL-4.0: β eff = 806 ± 10 [pcm], = 31.71 ± 0.07 [μs], (β eff /Λ)
cal
J40 (MCNP6.1)
= 254.05 ± 3.07 [s -1 ]; C/E = (β eff /Λ)
cal
J40 / (β eff /Λ)
exp