Chapter 8
Sensitivity and Uncertainty of Criticality
Masao Yamanaka
Abstract Excess reactivity and control rod worth are generally considered important
reactor physics parameters for experimentally examining the neutron characteristics
of criticality in a core, and for maintaining safe operation of the reactor core in terms
of neutron multiplication in the core. For excess reactivity and control rod worth
at KUCA, as well as at the Fast Critical Assembly in the Japan Atomic Energy
Agency, special attention is given to analyzing the uncertainty induced by nuclear
data libraries based on experimental data of criticality in representative cores (EE1
and E3 cores). Also, the effect of decreasing uncertainty on the accuracy of criticality is discussed in this study. At KUCA, experimental results are accumulated by
measurements of excess reactivity and control rod worth. To evaluate the accuracy of
experiments for benchmarks, the uncertainty originated from modeling of the core
configuration should be discussed in addition to uncertainty induced by nuclear data,
since the uncertainty from modeling has a potential to cover the eigenvalue bias more
than uncertainty by nuclear data. Here, to investigate the uncertainty of criticality
depending on the neutron spectrum of cores, it is very useful to analyze the reactivity
of a large number of measurements in typical hard (EE1) and soft (E3) spectrum
cores at KUCA.
Keywords Sensitivity · Uncertainty · Criticality · Solid-moderated and
solid-reflected core
M. Yamanaka (B)
Institute for Integrated Radiation and Nuclear Science, Kyoto University, Osaka, Japan
e-mail: yamanaka.masao.6z@kyoto-u.ac.jp
© The Author(s) 2021
C. H. Pyeon (ed.), Accelerator-Driven System at Kyoto University Critical Assembly,
https://doi.org/10.1007/978-981-16-0344-0_8
215
Sensitivity and Uncertainty of Criticality
Masao Yamanaka
Abstract Excess reactivity and control rod worth are generally considered important
reactor physics parameters for experimentally examining the neutron characteristics
of criticality in a core, and for maintaining safe operation of the reactor core in terms
of neutron multiplication in the core. For excess reactivity and control rod worth
at KUCA, as well as at the Fast Critical Assembly in the Japan Atomic Energy
Agency, special attention is given to analyzing the uncertainty induced by nuclear
data libraries based on experimental data of criticality in representative cores (EE1
and E3 cores). Also, the effect of decreasing uncertainty on the accuracy of criticality is discussed in this study. At KUCA, experimental results are accumulated by
measurements of excess reactivity and control rod worth. To evaluate the accuracy of
experiments for benchmarks, the uncertainty originated from modeling of the core
configuration should be discussed in addition to uncertainty induced by nuclear data,
since the uncertainty from modeling has a potential to cover the eigenvalue bias more
than uncertainty by nuclear data. Here, to investigate the uncertainty of criticality
depending on the neutron spectrum of cores, it is very useful to analyze the reactivity
of a large number of measurements in typical hard (EE1) and soft (E3) spectrum
cores at KUCA.
Keywords Sensitivity · Uncertainty · Criticality · Solid-moderated and
solid-reflected core
M. Yamanaka (B)
Institute for Integrated Radiation and Nuclear Science, Kyoto University, Osaka, Japan
e-mail: yamanaka.masao.6z@kyoto-u.ac.jp
© The Author(s) 2021
C. H. Pyeon (ed.), Accelerator-Driven System at Kyoto University Critical Assembly,
https://doi.org/10.1007/978-981-16-0344-0_8
215