4 Effective Delayed Neutron Fraction
111
almost the same as the measured ones at shallow subcritical states (Cases I-1 to I-5).
At deep subcriticality, however, the λ-mode calculations showed a large difference
as compared with the experiments. Conversely, ω-mode calculations correctly evaluated the experiments in the whole range except for Case III, indicating that the
kinetics parameters were not correctly evaluated by the λ-mode calculation even for
target subcriticality in ADS for Case IV (k eff = 0.97).
Here, ρ
MCNP
$
by λ-mode calculation showed agreement with measured ρ $ even
in deep subcritical states, as shown in Figs. 4.7 and 4.8. Conversely, as shown in
Figs. 4.9 and 4.10, from the comparison of α values, it was observed that the large
discrepancy between experiments and calculations as subcriticality becomes deeper.
The discrepancy in the comparison between the experiment and the calculation was
considered attributable to value for estimating calculated α value by Eq. (4.45).
The difference of value between λ-mode and ω-mode calculations could be also
explained by comparing between ρ $ and β eff / since ρ $ values agreed between the
experiment and the λ-mode calculation more accurately than the results of β eff /
(Fig. 4.11).
4.3.3.2 Discussion
The discussion is focused on the variation of each kinetics parameter by the calculations toward the subcriticality. β eff and were compared in terms of the λ-mode
or the ω-mode calculation as shown in Fig. 4.12. The values of β eff were independent of subcriticality in ω-mode calculations; however, λ-mode calculations showed
a slightly increased tendency toward subcriticality. Notably, values revealed a
different tendency compared with β eff values under λ-mode and ω-mode calculations. Furthermore, β eff values were equivalent in Cases I-5 and IV; by contrast,
however, values were different even at almost the same subcritical states, indicating
that is sensitive to the size of the core and to the insertion of control rods.
Fig. 4.12 Relationship
between calculated β eff and
for subcriticality variation
(Ref. [15])
20
30
40
50
60
820
840
860
880
I-1
(523)
I-2
(607)
I-3
(910)
I-4
(673)
I-5
(1051)
II
(378)
III
(690)
IV
(1026)
V
(1159)
VI
(1238)
VII
(1669)
Generation time [ s]
Effective delayed neutron fraction
eff [pcm]
Case
(α value in ω-mode by PARTISN)
βeff
λ-mode in PARTISN
ω-mode in PARTISN
MCNP6.1
λ-mode in PARTISN
ω-mode in PARTISN
eff :
111
almost the same as the measured ones at shallow subcritical states (Cases I-1 to I-5).
At deep subcriticality, however, the λ-mode calculations showed a large difference
as compared with the experiments. Conversely, ω-mode calculations correctly evaluated the experiments in the whole range except for Case III, indicating that the
kinetics parameters were not correctly evaluated by the λ-mode calculation even for
target subcriticality in ADS for Case IV (k eff = 0.97).
Here, ρ
MCNP
$
by λ-mode calculation showed agreement with measured ρ $ even
in deep subcritical states, as shown in Figs. 4.7 and 4.8. Conversely, as shown in
Figs. 4.9 and 4.10, from the comparison of α values, it was observed that the large
discrepancy between experiments and calculations as subcriticality becomes deeper.
The discrepancy in the comparison between the experiment and the calculation was
considered attributable to value for estimating calculated α value by Eq. (4.45).
The difference of value between λ-mode and ω-mode calculations could be also
explained by comparing between ρ $ and β eff / since ρ $ values agreed between the
experiment and the λ-mode calculation more accurately than the results of β eff /
(Fig. 4.11).
4.3.3.2 Discussion
The discussion is focused on the variation of each kinetics parameter by the calculations toward the subcriticality. β eff and were compared in terms of the λ-mode
or the ω-mode calculation as shown in Fig. 4.12. The values of β eff were independent of subcriticality in ω-mode calculations; however, λ-mode calculations showed
a slightly increased tendency toward subcriticality. Notably, values revealed a
different tendency compared with β eff values under λ-mode and ω-mode calculations. Furthermore, β eff values were equivalent in Cases I-5 and IV; by contrast,
however, values were different even at almost the same subcritical states, indicating
that is sensitive to the size of the core and to the insertion of control rods.
Fig. 4.12 Relationship
between calculated β eff and
for subcriticality variation
(Ref. [15])
20
30
40
50
60
820
840
860
880
I-1
(523)
I-2
(607)
I-3
(910)
I-4
(673)
I-5
(1051)
II
(378)
III
(690)
IV
(1026)
V
(1159)
VI
(1238)
VII
(1669)
Generation time [ s]
Effective delayed neutron fraction
eff [pcm]
Case
(α value in ω-mode by PARTISN)
βeff
λ-mode in PARTISN
ω-mode in PARTISN
MCNP6.1
λ-mode in PARTISN
ω-mode in PARTISN
eff :