70
C. H. Pyeon
in the previous study [20], to get a better understanding of the time behavior of the
kinetic parameters.
Furthermore, most of the C/E values demonstrated a notably greater tendency
of the calculation results to the deep subcriticality attributable to the effect of the
spallation neutrons on neutron flux, whereas the value of Fiber #1 by the PNS method
showed a decreasing tendency.
3.2.2.2 Evaluation of β eff /
For the α-fitting method, prompt neutron decay constant α is easily deduced by
combining subcriticality ρ in pcm units, effective delayed neutron fraction β eff , and
neutron generation time as follows:
α =
β eff − ρ
Λ
.
(3.5)
Using the relationship between ρ and ρ $ in pcm and dollar units shown in Eq. (3.2),
respectively, ρ $ can be expressed as follows:
ρ $ = −
Λ
β eff
α −
β eff
Λ
.
(3.6)
Assuming that the experimental results of α and ρ $ validate the accuracy of
kinetics parameters, the value of was deduced by Eq. (3.6), as shown in Table 3.9,
with the combined use of the measured α and ρ $ , and the calculated β eff . Through
the experimental analyses of the ADS with spallation neutrons in KUCA, a previous
study [21] has clearly demonstrated that the value of β eff has a small effect on the evaluation of subcriticality in pcm units converted from that in dollar units, as compared
with the results of numerical subcriticality in pcm units. Here, considering the characteristics of β eff , attention was directed to another kinetic parameter, , obtained
with the combined use of α and ρ $ by varying the subcriticality. The deduction of
in Fiber #2 was based on Eq. (3.6), by using the value of β eff obtained from the
MCNP6.1 calculations, since the experimental results of Fiber #2 by the PNS method
showed a relatively good agreement with the numerical simulations, as described in
Sect. 3.2.2.1. As shown in Table 3.9, a comparison between the experimental and
the numerical values of demonstrated the same tendency as the acceptable relative
difference between MCNP6.1 and Fiber #2 by varying the subcriticality. Furthermore, using the experimental results of α and ρ $ of Fibers #1 and #2 by the PNS
method, the fitting lines (Fiber #1: ρ $ = −12.27E-03α +4.10; Fiber #2: ρ $ = −
6.82E-03α +1.27) by Eq. (3.5) were obtained with the values of the gradient (Fiber
#1: −12.27E-03; Fiber #2: −6.82E-03) of /β eff as shown in Fig. 3.11, as compared
with the results of MCNP6.1, Fibers #1 and #2 shown in Table 3.10. The experimental
fitting of Fiber #2 demonstrated good agreement with the MCNP6.1 calculations by
varying the subcriticality, although the relative difference between the experiments
C. H. Pyeon
in the previous study [20], to get a better understanding of the time behavior of the
kinetic parameters.
Furthermore, most of the C/E values demonstrated a notably greater tendency
of the calculation results to the deep subcriticality attributable to the effect of the
spallation neutrons on neutron flux, whereas the value of Fiber #1 by the PNS method
showed a decreasing tendency.
3.2.2.2 Evaluation of β eff /
For the α-fitting method, prompt neutron decay constant α is easily deduced by
combining subcriticality ρ in pcm units, effective delayed neutron fraction β eff , and
neutron generation time as follows:
α =
β eff − ρ
Λ
.
(3.5)
Using the relationship between ρ and ρ $ in pcm and dollar units shown in Eq. (3.2),
respectively, ρ $ can be expressed as follows:
ρ $ = −
Λ
β eff
α −
β eff
Λ
.
(3.6)
Assuming that the experimental results of α and ρ $ validate the accuracy of
kinetics parameters, the value of was deduced by Eq. (3.6), as shown in Table 3.9,
with the combined use of the measured α and ρ $ , and the calculated β eff . Through
the experimental analyses of the ADS with spallation neutrons in KUCA, a previous
study [21] has clearly demonstrated that the value of β eff has a small effect on the evaluation of subcriticality in pcm units converted from that in dollar units, as compared
with the results of numerical subcriticality in pcm units. Here, considering the characteristics of β eff , attention was directed to another kinetic parameter, , obtained
with the combined use of α and ρ $ by varying the subcriticality. The deduction of
in Fiber #2 was based on Eq. (3.6), by using the value of β eff obtained from the
MCNP6.1 calculations, since the experimental results of Fiber #2 by the PNS method
showed a relatively good agreement with the numerical simulations, as described in
Sect. 3.2.2.1. As shown in Table 3.9, a comparison between the experimental and
the numerical values of demonstrated the same tendency as the acceptable relative
difference between MCNP6.1 and Fiber #2 by varying the subcriticality. Furthermore, using the experimental results of α and ρ $ of Fibers #1 and #2 by the PNS
method, the fitting lines (Fiber #1: ρ $ = −12.27E-03α +4.10; Fiber #2: ρ $ = −
6.82E-03α +1.27) by Eq. (3.5) were obtained with the values of the gradient (Fiber
#1: −12.27E-03; Fiber #2: −6.82E-03) of /β eff as shown in Fig. 3.11, as compared
with the results of MCNP6.1, Fibers #1 and #2 shown in Table 3.10. The experimental
fitting of Fiber #2 demonstrated good agreement with the MCNP6.1 calculations by
varying the subcriticality, although the relative difference between the experiments