2 Subcriticality
47
The Degweker’s factor (m 2 − m
2
1 )/m
2
1 of 0.067 ± 0.011, which is a quantitative indication of the non-Poisson character, could be determined from the present Rossi-α
analysis.
The power spectral analysis on frequency domain was conducted in the same Acore as the above Feynman-α and Rossi-α analyses. Not only the cross-power but also
the auto-power spectral density had a considerable correlated noise component even
at a deeply subcritical state, where no correlated component could be observed under
a pulsed DT(14 MeV) neutron source. The non-Poisson character of the spallation
source must enhance the correlation amplitude of these power spectral densities. The
Degweker’s factor of 0.082 ± 0.021 could be determined from the present analysis
and was consistent with that obtained by the above Rossi-α analysis.
An experimental technique based on accelerator-beam trip and restart operation
was proposed to determine the subcritical reactivity of ADS. A series of these experiments was performed in a subcritical thermal core of KUCA. The results demonstrated the applicability of the proposed technique to the thermal ADS of KUCA.
We expect the proposed technique to be applied for an actual ADS in start-up or
shut-down operation.
References
1. Nakajima K, Sano T, Hohara S et al (2021) Feynman-α and Rossi-α analyses for a subcritical reactor system driven by a pulsed spallation neutron source in Kyoto University Critical
Assembly. J Nucl Sci Technol 58:117
2. Nakajima K, Sano T, Takahashi et al (2020) Source multiplication measurements and neutron
correlation analyses for a highly enriched uranium subcritical core driven by an inherent source
in Kyoto University Critical Assembly. J Nucl Sci Technol 57:1152
3. Nagaya Y, Okumura K, Sakurai T et al (2016) MVP/GMVP Version3: general purpose Monte
Carlo codes for neutron and photon transport calculations based on continuous energy and
multigroup methods. JAEA-Data/Code 2016-018
4. Nagaya Y, Okumura K, Mori T (2015) Recent developments of JAEA’s Monte Carlo code
MVP for reactor physics applications. Ann Nucl Energy 82:85
5. Shibata K, Iwamoto O, Nakagawa T et al (2011) JENDL-4.0: a new library for nuclear science
and technology. J Nucl Sci Technol 48:1
6. Rana YS, Degweker SB (2009) Feynman-alpha and Rossi-alpha formulas with delayed
neutrons for subcritical reactors driven by pulsed non-poisson sources. Nucl Sci Eng 162:117
7. Williams MMR (1974) Random processes in nuclear reactors. Pergamon Press, Oxford, UK,
pp 26–49
8. Degweker SB, Rana YS (2007) Reactor noise in accelerator driven systems-II. Ann Nucl Energy
34:463
9. Okuda R, Sakon A, Hohara S et al (2016) An improved Feynman-α analysis with a movingbunching technique. J Nucl Sci Technol 53:1647
10. Tonoike K, Miyoshi Y, Kikuchi T et al (2002) Kinetic parameter βeff/ measurement on low
enriched uranyl nitrate solution with single unit cores (600ϕ, 280T, 800ϕ) of STACY. J Nucl
Sci Technol 39:1227
11. Taninaka H, Hashimoto K, Pyeon CH et al (2010) Determination of lambda-mode eigenvalue
separation of a thermal accelerator-driven system from pulsed neutron experiment. J Nucl Sci
Technol 47:376
47
The Degweker’s factor (m 2 − m
2
1 )/m
2
1 of 0.067 ± 0.011, which is a quantitative indication of the non-Poisson character, could be determined from the present Rossi-α
analysis.
The power spectral analysis on frequency domain was conducted in the same Acore as the above Feynman-α and Rossi-α analyses. Not only the cross-power but also
the auto-power spectral density had a considerable correlated noise component even
at a deeply subcritical state, where no correlated component could be observed under
a pulsed DT(14 MeV) neutron source. The non-Poisson character of the spallation
source must enhance the correlation amplitude of these power spectral densities. The
Degweker’s factor of 0.082 ± 0.021 could be determined from the present analysis
and was consistent with that obtained by the above Rossi-α analysis.
An experimental technique based on accelerator-beam trip and restart operation
was proposed to determine the subcritical reactivity of ADS. A series of these experiments was performed in a subcritical thermal core of KUCA. The results demonstrated the applicability of the proposed technique to the thermal ADS of KUCA.
We expect the proposed technique to be applied for an actual ADS in start-up or
shut-down operation.
References
1. Nakajima K, Sano T, Hohara S et al (2021) Feynman-α and Rossi-α analyses for a subcritical reactor system driven by a pulsed spallation neutron source in Kyoto University Critical
Assembly. J Nucl Sci Technol 58:117
2. Nakajima K, Sano T, Takahashi et al (2020) Source multiplication measurements and neutron
correlation analyses for a highly enriched uranium subcritical core driven by an inherent source
in Kyoto University Critical Assembly. J Nucl Sci Technol 57:1152
3. Nagaya Y, Okumura K, Sakurai T et al (2016) MVP/GMVP Version3: general purpose Monte
Carlo codes for neutron and photon transport calculations based on continuous energy and
multigroup methods. JAEA-Data/Code 2016-018
4. Nagaya Y, Okumura K, Mori T (2015) Recent developments of JAEA’s Monte Carlo code
MVP for reactor physics applications. Ann Nucl Energy 82:85
5. Shibata K, Iwamoto O, Nakagawa T et al (2011) JENDL-4.0: a new library for nuclear science
and technology. J Nucl Sci Technol 48:1
6. Rana YS, Degweker SB (2009) Feynman-alpha and Rossi-alpha formulas with delayed
neutrons for subcritical reactors driven by pulsed non-poisson sources. Nucl Sci Eng 162:117
7. Williams MMR (1974) Random processes in nuclear reactors. Pergamon Press, Oxford, UK,
pp 26–49
8. Degweker SB, Rana YS (2007) Reactor noise in accelerator driven systems-II. Ann Nucl Energy
34:463
9. Okuda R, Sakon A, Hohara S et al (2016) An improved Feynman-α analysis with a movingbunching technique. J Nucl Sci Technol 53:1647
10. Tonoike K, Miyoshi Y, Kikuchi T et al (2002) Kinetic parameter βeff/ measurement on low
enriched uranyl nitrate solution with single unit cores (600ϕ, 280T, 800ϕ) of STACY. J Nucl
Sci Technol 39:1227
11. Taninaka H, Hashimoto K, Pyeon CH et al (2010) Determination of lambda-mode eigenvalue
separation of a thermal accelerator-driven system from pulsed neutron experiment. J Nucl Sci
Technol 47:376