120
M. Yamanaka
On the basis of the validity of (β eff /Λ)
exp mentioned in Sect. 4.4.2, Eq. (4.55) can
be interpreted as a kind of Lambda ratio between the experiments and the calculations,
with the combined use of (β eff /Λ)
cal
super−critical and (β eff /Λ)
exp . Actually, the value of
(β eff /Λ)
exp obtained by the ADS experiments at KUCA can be used as an index
of in the near-critical configurations, and is, indeed, expected to be applied for
the validation of , by stochastic and deterministic calculations, at near-critical
configurations in a thermal neutron spectrum core.
4.5 Conclusion
A calculation methodology of β
RR
source by the k-ratio method with an external neutron
source has been proposed for the subcriticality estimation. Subcriticality measurements were carried at the KUCA-A cores to examine its applicability of the proposed
calculation methodology by varying the subcriticality and the external neutron
source. To confirm the validity of the proposed methodology, the eigenvalue calculations were firstly performed to estimate the multiplication factor k RR with reaction rates by MCNPX. Further, β
RR
eigen by the k-ratio method with reaction rates was
compared with the reference ones obtained by MCNP6.1, respectively. For the estimation of subcriticality by the fixed-source calculations, β
RR
source was observed to be
dependent on the variation of subcriticality and external neutron source. Finally, the
subcriticality with β
RR
source was acquired well ranging between about 0.99 and 0.97
in k eff and revealed the comparative tendency in the deep subcriticality through the
estimation with the use of β
RR
source obtained by the proposed calculation methodology.
In the methodology for estimating the value of β eff , the Rossi-α method was
applied to the neutron noise analyses at the PNS experiments with pulsed spallation
neutrons. With the fitting curve obtained by neutron noise analyses, the signals from
two detectors installed at the center of the core (optical fiber detector) and outside
the core (BF 3 detector) and the correction factors, β eff was measured and compared
with the value calculated by MCNP6.1. The optical fiber detector located at the core
center showed that the accuracy of the measured value, compared with the calculated
one, was within a relative difference of about 13% in the subcritical range of the ADS
operation around k eff = 0.93. The result with BF 3 detector installed outside the core
was not compared with the calculated one because of the low accuracy attributed to the
uncorrelated probability. The applicability of the measurement methodology based
on the Rossi-α method was demonstrated by the comparison between calculated and
measured β eff values in ADS experiments with spallation neutrons.
M. Yamanaka
On the basis of the validity of (β eff /Λ)
exp mentioned in Sect. 4.4.2, Eq. (4.55) can
be interpreted as a kind of Lambda ratio between the experiments and the calculations,
with the combined use of (β eff /Λ)
cal
super−critical and (β eff /Λ)
exp . Actually, the value of
(β eff /Λ)
exp obtained by the ADS experiments at KUCA can be used as an index
of in the near-critical configurations, and is, indeed, expected to be applied for
the validation of , by stochastic and deterministic calculations, at near-critical
configurations in a thermal neutron spectrum core.
4.5 Conclusion
A calculation methodology of β
RR
source by the k-ratio method with an external neutron
source has been proposed for the subcriticality estimation. Subcriticality measurements were carried at the KUCA-A cores to examine its applicability of the proposed
calculation methodology by varying the subcriticality and the external neutron
source. To confirm the validity of the proposed methodology, the eigenvalue calculations were firstly performed to estimate the multiplication factor k RR with reaction rates by MCNPX. Further, β
RR
eigen by the k-ratio method with reaction rates was
compared with the reference ones obtained by MCNP6.1, respectively. For the estimation of subcriticality by the fixed-source calculations, β
RR
source was observed to be
dependent on the variation of subcriticality and external neutron source. Finally, the
subcriticality with β
RR
source was acquired well ranging between about 0.99 and 0.97
in k eff and revealed the comparative tendency in the deep subcriticality through the
estimation with the use of β
RR
source obtained by the proposed calculation methodology.
In the methodology for estimating the value of β eff , the Rossi-α method was
applied to the neutron noise analyses at the PNS experiments with pulsed spallation
neutrons. With the fitting curve obtained by neutron noise analyses, the signals from
two detectors installed at the center of the core (optical fiber detector) and outside
the core (BF 3 detector) and the correction factors, β eff was measured and compared
with the value calculated by MCNP6.1. The optical fiber detector located at the core
center showed that the accuracy of the measured value, compared with the calculated
one, was within a relative difference of about 13% in the subcritical range of the ADS
operation around k eff = 0.93. The result with BF 3 detector installed outside the core
was not compared with the calculated one because of the low accuracy attributed to the
uncorrelated probability. The applicability of the measurement methodology based
on the Rossi-α method was demonstrated by the comparison between calculated and
measured β eff values in ADS experiments with spallation neutrons.