Abstract
The subcritical multiplication factor
k
s
and the external neutron source efficiency
φ
∗
are important parameters in the accelerator-driven system (ADS) performance assessment. The theoretical relation between
k
s
and the effective multiplication factor
k
eff
in a subcritical system is discussed in different cases of subcritical system. On the basis of the theoretical background, the dependence of
k
s
and
φ
∗
on subcriticality, source position, and energy is numerically investigated using a simple thermal subcritical model. For the sake of experimental evaluation of
k
s
and
φ
∗
, the ADS experiments have been carried out in the subcritical systems combined with 14
MeV pulsed neutrons of the Kyoto University Critical Assembly (KUCA). The
k
s
and
φ
∗
parameters are successfully measured by utilizing the reaction rate distribution obtained by the optical fiber detectors in the subcritical system, within a relative difference of less than 7% and 12% for
k
s
and
φ
∗
, respectively, between measured and calculated values for most studied cases.