114
M. Yamanaka
4.4.1.3 Kinetics Parameters
For the α-fitting method [25], α is easily deduced by combining subcriticality (−ρ pcm )
in pcm units, β eff and as follows:
α =
β eff − ρ pcm
Λ
.
(4.50)
The relationship between ρ pcm and ρ $ is expressed with the use of β eff as follows:
ρ pcm = ρ $ β eff .
(4.51)
Substituting Eq. (4.51) for Eq. (4.50), β eff / can be expressed as follows:
β eff
Λ
=
α
1 − ρ $
.
(4.52)
The value of β eff / is easily deduced from the experimental results of α and ρ $ .
4.4.2 Results and Discussion
4.4.2.1 Eigenvalue Calculations
For transport, numerical calculations were performed by the Monte Carlo transport
code, MCNP6.1 together with nuclear data libraries, JENDL-4.0 and ENDF/B-VII.1.
Here, in MCNP6.1, since the effects of reactivity by neutron detectors (optical fiber
detectors, BF-3 detectors, fission chambers, and uncompensated ionization chambers) and control (safety) rods are not negligible, neutron detectors and control
(safety) rods were modeled precisely in the simulated geometry and transport calculations. The precision of numerical criticality in pcm units was attained by the eigenvalue calculations with a total of 5 × 10
8 histories (1 × 10
5 histories per cycle, 5
× 10
3 active cycles, and 1 × 10
2 skip cycles) and a statistical error of about 4 pcm.
Also, main kinetics parameters, β eff , and Rossi-α (termed β eff / in MCNP6.1)
values were obtained by the eigenvalue calculations, when obtaining the effective
multiplication factor by the k-code option.
To confirm the numerical precision of eigenvalue calculations by MCNP6.1,
excess reactivity and control rod worth (C1, C2, and C3) were compared with those
obtained from the experiments by the positive period method and the rod drop method,
respectively. The MCNP eigenvalue calculations in the critical state are not always
unit, differing from the experimental results in critical state obtained by nuclear data
accuracy and uniformed number density approximation in core materials, although
a critical core configuration is more closely simulated by MCNP. Thus, excess reactivity ρ
cal
excess in pcm units was numerically deduced by the difference between two
M. Yamanaka
4.4.1.3 Kinetics Parameters
For the α-fitting method [25], α is easily deduced by combining subcriticality (−ρ pcm )
in pcm units, β eff and as follows:
α =
β eff − ρ pcm
Λ
.
(4.50)
The relationship between ρ pcm and ρ $ is expressed with the use of β eff as follows:
ρ pcm = ρ $ β eff .
(4.51)
Substituting Eq. (4.51) for Eq. (4.50), β eff / can be expressed as follows:
β eff
Λ
=
α
1 − ρ $
.
(4.52)
The value of β eff / is easily deduced from the experimental results of α and ρ $ .
4.4.2 Results and Discussion
4.4.2.1 Eigenvalue Calculations
For transport, numerical calculations were performed by the Monte Carlo transport
code, MCNP6.1 together with nuclear data libraries, JENDL-4.0 and ENDF/B-VII.1.
Here, in MCNP6.1, since the effects of reactivity by neutron detectors (optical fiber
detectors, BF-3 detectors, fission chambers, and uncompensated ionization chambers) and control (safety) rods are not negligible, neutron detectors and control
(safety) rods were modeled precisely in the simulated geometry and transport calculations. The precision of numerical criticality in pcm units was attained by the eigenvalue calculations with a total of 5 × 10
8 histories (1 × 10
5 histories per cycle, 5
× 10
3 active cycles, and 1 × 10
2 skip cycles) and a statistical error of about 4 pcm.
Also, main kinetics parameters, β eff , and Rossi-α (termed β eff / in MCNP6.1)
values were obtained by the eigenvalue calculations, when obtaining the effective
multiplication factor by the k-code option.
To confirm the numerical precision of eigenvalue calculations by MCNP6.1,
excess reactivity and control rod worth (C1, C2, and C3) were compared with those
obtained from the experiments by the positive period method and the rod drop method,
respectively. The MCNP eigenvalue calculations in the critical state are not always
unit, differing from the experimental results in critical state obtained by nuclear data
accuracy and uniformed number density approximation in core materials, although
a critical core configuration is more closely simulated by MCNP. Thus, excess reactivity ρ
cal
excess in pcm units was numerically deduced by the difference between two