The Space Dependence of Reactor Noise I-Theory

Sheff, J.R.; Albrecht, R.W.

doi:10.13182/nse66-a17638

Cited by 35 publications

(5 citation statements)

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“…When certain a higher prompt mode as well as a fundamental prompt mode are excited, such a higher term as the second term of the above equation can be added to the fundamental term of the power spectral density [25][26][27]. The prompt-neutron decay constant of the higher mode is represented by α H .…”

Section: Formula Applied To Present Analysesmentioning

confidence: 99%

Subcriticality

Hashimoto

2021

Accelerator-Driven System at Kyoto University Critical Assembly

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For a subcritical reactor system driven by a periodically pulsed spallation neutron source in KUCA, the Feynman-α and the Rossi-α neutron correlation analyses are conducted to determine the prompt neutron decay constant and quantitatively to confirm a non-Poisson character of the neutron source. The decay constant determined from the present Feynman-α analysis well agrees with that from a previous analysis for the same subcritical system driven by an inherent source. Considering the effect of a higher mode excited, the disagreement can be successfully resolved. The power spectral analysis on frequency domain is also carried out. Not only the cross-power but also the auto-power spectral density have a considerable correlated component even at a deeply subcritical state, where no correlated component could be previously observed under a 14 MeV neutron source. The indicator of the non-Poisson character of the present spallation source can be obtained from the spectral analysis and is consistent with that from the Rossi-α analysis. An experimental technique based on an accelerator-beam trip or restart operation is proposed to determine the subcritical reactivity of ADS. Applying the least-squares inverse kinetics method to the data analysis, the subcriticality can be inferred from time-sequence neutron count data after these operations.

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Section: Formula Applied To Present Analysesmentioning

confidence: 99%

Subcriticality

Hashimoto

2021

Accelerator-Driven System at Kyoto University Critical Assembly

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“…Neutron noise measurements generally require sensitive detectors to minimize detector shape or other spatial effects [6]. The BF3 detector has a sensitivity of 4.7×10 -2 counts/nth with an active length of 100 mm and a 7.5 mm diameter.…”

Section: Limitations and Motivation For Current Mode Measurementmentioning

confidence: 99%

Current Mode Neutron Noise Measurements in the Zero Power Reactor CROCUS

Pakari

Lamirand²,

Perret

et al. 2018

EPJ Web Conf.

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Abstract-The present article is an overview of developments and results regarding neutron noise measurements in current mode at the CROCUS zero power facility. Neutron noise measurements offer a non-invasive method to determine kinetic reactor parameters such as the prompt decay constant at criticality α = βeff / Λ, the effective delayed neutron fraction βeff, and the mean generation time Λ for code validation efforts. At higher detection rates, i.e. above 2×10 4 cps in the used configuration at 0.1 W, the previously employed pulse charge amplification electronics with BF3 detectors yielded erroneous results due to dead time effects. Future experimental needs call for higher sensitivity in detectors, higher detection rates or higher reactor powers, and thus a generally more versatile measurement system. We, therefore, explored detectors operated with current mode acquisition electronics to accommodate the need. We approached the matter in two ways: 1) By using the two compensated , also within 1σ agreement. The improvements to previous neutron noise measurements include shorter measurement durations that can achieve comparable statistical uncertainties and measurements at higher detection rates.

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“…This is because the peak data contain so slight contribution of the higher mode that the least-squares method cannot estimate two parameters of the second term of Equations (35) and (36). Akcasu et al [36] and Sheff et al [37] presented a general space-dependent formula of the power spectral density for a stationary neutron source, by employing the modal expansion technique. Analogous to their formulations, Equations (35) and (36) were extended to include a higher-mode contribution, where the sum over spatial modes was truncated at a dominant higher mode.…”

Section: Inference Of Prompt-neutron Decay Constant From Uncorrelatedmentioning

confidence: 99%

Power spectral analysis for a thermal subcritical reactor system driven by a pulsed 14 MeV neutron source

Sakon

Hashimoto

Sugiyama

et al. 2013

Journal of Nuclear Science and Technology

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A series of power spectral analyses for a thermal subcritical reactor system driven by a pulsed 14 MeV neutron source was carried out at Kyoto University Critical Assembly (KUCA), to determine the promptneutron decay constant of the accelerator-driven system (ADS). The cross-power spectral density between time-sequence signal data of two neutron detectors was composed of a familiar continuous reactor noise component and many delta-function-like peaks at the integral multiple of pulse repetition frequency. The prompt-neutron decay constant inferred from the reactor noise component of the cross-power spectral density was consistent with that obtained by a pulsed neutron experiment. However, the reactor noise component of the auto-power spectral density of each detector was hidden by a white chamber noise in the higher-frequency range and this feature resulted in a considerable underestimation of the decay constant. For several runs with a low pulse-repetition frequency, furthermore, we attempted to infer the decay constant from point data of the delta-function-like peaks. The analysis for a run under a slightly subcritical state resulted in the consistent decay constant; however, those for other runs under significantly subcritical states underestimated the decay constant. Considering the contribution of a spatially higher mode to the point data, the above underestimation was solved to obtain the consistent decay constant. While the Feynman-α formula for a pulsed neutron source is too complicated to be fitted directly to variance-to-mean ratio data, the present analysis on frequency domain is much simpler and the conventional formula based on the first-order reactor transfer function is available for fitting to power spectral density data.

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The Space Dependence of Reactor Noise I-Theory

Cited by 35 publications

References 0 publications

Subcriticality

Subcriticality

Current Mode Neutron Noise Measurements in the Zero Power Reactor CROCUS

Power spectral analysis for a thermal subcritical reactor system driven by a pulsed 14 MeV neutron source

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