4 Effective Delayed Neutron Fraction
121
ADS experiments were carried out to evaluate β eff / values by varying detector
type, detector position, external neutron source, and subcriticality. The capability of
λ-mode and ω-mode calculations was examined by comparing directly measured ρ $ ,
α, and β eff / in the PNS experiment with the target subcriticality of ADS ranging
between 500 and 7500 pcm. The measurement of ρ $ and α indicated slight dependence on an external neutron source but not on any spatial effect except for the BF 3
detector located near the neutron source. In the experimental analyses, calculated ρ $
(λ-mode and ω-mode) showed good agreement with measured ρ $ within the whole
range of subcriticality; however, the value of α by the λ-mode calculation showed
a difference in the experiment at deep subcriticality. Conversely, α obtained by the
ω-mode calculation agreed with the experiments. The calculated results of β eff /
were compared with the measured ones to examine their capability under subcriticality variation; consequently, an agreement was observed between the experiments
and ω-mode calculations under a wide range of subcriticality. Notably, however,
the λ-mode calculations differed from the experiments even under slight subcriticality, implying the necessity of introducing ω-mode calculations in ADS design for
evaluating actual neutron multiplication factor in the subcritical system and kinetics
parameters.
Main kinetics parameters, α and ρ $ , were experimentally obtained from the
KUCA core, and β eff and , were numerically validated by MCNP6.1, at the nearcritical configurations: super-critical and subcritical states. The experimental value
of (β eff /Λ)
exp was then available for use as an index of in the near-critical configurations, with an attempt at the validation of by the numerical calculations. From
the results of experimental and numerical analyses, the importance of the experimental value of (β eff /Λ)
exp was emphasized for the verification of , since the
kinetics parameters were successfully obtained from the clean cores of near-critical
configurations (super-critical and subcritical states) in the thermal spectrum core.
References
1. Gozani T (1962) A modified procedure for the evaluation of pulsed source experiments in
subcritical reactors. Nukleonik 4:348
2. Yamanaka M, Pyeon CH, Misawa T (2016) Monte Carlo approach of effective delayed neutron
fraction by k-ratio method with external neutron source. Nucl Sci Eng 184:551
3. Yagi T, Misawa T, Pyeon CH (2011) A small high sensitivity neutron detector using a
wavelength shifting fiber. Appl Radiat Isot 69:176
4. Hendricks JS et al (2005) MCNPX user’s manual, version 2.5.0. LA-UR-05-2675
5. Chadwick MB, Obložinský P, Herman M et al (2006) ENDF/B-VII.0: next generation evaluated
nuclear data library for nuclear science and technology. Nucl Data Sheets 107:2931
6. Bretscher MM (1997) Perturbation independent methods for calculating research reactor kinetic
parameters. ANL/RERTR/TM30
121
ADS experiments were carried out to evaluate β eff / values by varying detector
type, detector position, external neutron source, and subcriticality. The capability of
λ-mode and ω-mode calculations was examined by comparing directly measured ρ $ ,
α, and β eff / in the PNS experiment with the target subcriticality of ADS ranging
between 500 and 7500 pcm. The measurement of ρ $ and α indicated slight dependence on an external neutron source but not on any spatial effect except for the BF 3
detector located near the neutron source. In the experimental analyses, calculated ρ $
(λ-mode and ω-mode) showed good agreement with measured ρ $ within the whole
range of subcriticality; however, the value of α by the λ-mode calculation showed
a difference in the experiment at deep subcriticality. Conversely, α obtained by the
ω-mode calculation agreed with the experiments. The calculated results of β eff /
were compared with the measured ones to examine their capability under subcriticality variation; consequently, an agreement was observed between the experiments
and ω-mode calculations under a wide range of subcriticality. Notably, however,
the λ-mode calculations differed from the experiments even under slight subcriticality, implying the necessity of introducing ω-mode calculations in ADS design for
evaluating actual neutron multiplication factor in the subcritical system and kinetics
parameters.
Main kinetics parameters, α and ρ $ , were experimentally obtained from the
KUCA core, and β eff and , were numerically validated by MCNP6.1, at the nearcritical configurations: super-critical and subcritical states. The experimental value
of (β eff /Λ)
exp was then available for use as an index of in the near-critical configurations, with an attempt at the validation of by the numerical calculations. From
the results of experimental and numerical analyses, the importance of the experimental value of (β eff /Λ)
exp was emphasized for the verification of , since the
kinetics parameters were successfully obtained from the clean cores of near-critical
configurations (super-critical and subcritical states) in the thermal spectrum core.
References
1. Gozani T (1962) A modified procedure for the evaluation of pulsed source experiments in
subcritical reactors. Nukleonik 4:348
2. Yamanaka M, Pyeon CH, Misawa T (2016) Monte Carlo approach of effective delayed neutron
fraction by k-ratio method with external neutron source. Nucl Sci Eng 184:551
3. Yagi T, Misawa T, Pyeon CH (2011) A small high sensitivity neutron detector using a
wavelength shifting fiber. Appl Radiat Isot 69:176
4. Hendricks JS et al (2005) MCNPX user’s manual, version 2.5.0. LA-UR-05-2675
5. Chadwick MB, Obložinský P, Herman M et al (2006) ENDF/B-VII.0: next generation evaluated
nuclear data library for nuclear science and technology. Nucl Data Sheets 107:2931
6. Bretscher MM (1997) Perturbation independent methods for calculating research reactor kinetic
parameters. ANL/RERTR/TM30