Research and development on accelerator-driven transmutation system at JAERI

Maarof

et al. 2013

Large negative reactivity of a subcritical system driven by a pulsed 14 MeV neutron source has been measured in the Kyoto University Critical Assembly. The subcriticality of the accelerator-driven system (ADS) ranged in effective multiplication factor roughly from 0.98 to 0.92, which corresponded to an operational range of an actual ADS proposed by Japan Atomic Energy Agency. As the measurement technique, pulsed neutron method, power spectral analysis for pulsed neutron source, accelerator-beam trip method were employed. From neutron count decay data obtained by the pulsed neutron experiment, not only the promptneutron decay constant of fundamental mode but also a higher spatial mode could be derived. The subcriticality was also determined from the fundamental decay constant. The measured cross-power spectral density consisted of a familiar correlated reactor-noise component and many uncorrelated delta-functionlike peaks at the integral multiple of pulse repetition frequency. The fundamental prompt-neutron decay constant, i.e., the subcriticality determined from the latter uncorrelated peaks was consistent with that obtained by the above pulsed neutron experiment. However, the magnitude of the former correlated component was reduced with an increase in the subcriticality and eventually this component became almost white at deeply subcritical state ranging in the multiplication factor under 0.95. Consequently, the determination of the decay constant from the correlated component was impossible under such a subcritical state. As data analysis method for the beam trip experiment, both the conventional integral count method and the least-squares inverse kinetics method (LSIKM) were employed. The LSIKM analysis led to the consistent subcriticality with that obtained by the pulsed neutron experiment, while the integral count method significantly underestimated the subcriticality. This underestimation originated from a residual background count, which was maintained after the beam trip. The LSIKM was mostly not influenced by such a slight count rate.

Section: Cross-power Spectral Analysismentioning

confidence: 99%

“…Research and development of accelerator-driven system (ADS) has become of great interest in recent years [1][2][3][4][5][6][7][8]. The reactor system is operated at a subcritical state to enhance nuclear safety.…”

Section: Introductionmentioning

confidence: 99%

Measurement of large negative reactivity of an accelerator-driven system in the Kyoto University Critical Assembly

Sakon

Maarof

et al. 2013

“…ADS is expected to provide capabilities for power generation, nuclear waste transmutation, and a reliable neutron source for research purposes [4][5][6][7][8]. The reactor system is operated at a subcritical state to enhance nuclear safety and is driven by a spallation neutron source to achieve the above capabilities.…”

Section: Introductionmentioning

confidence: 99%

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

Sakon

Sugiyama

et al. 2013

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.

“…[1][2][3] ADS is expected to provide capabilities for power generation, nuclear waste transmutation, and a reliable neutron source for research purposes. [4][5][6][7][8] The reactor system is operated at a subcritical state to enhance nuclear safety and is driven by a spallation neutron source to achieve the above capabilities. The subcritical reactivity of the system indicates a safety margin from the viewpoint of criticality safety and governs a power gain of the system to the source neutron input.…”

Section: Introductionmentioning

confidence: 99%

Determination of Subcritical Reactivity of a Thermal Accelerator-Driven System from Beam Trip and Restart Experiment

Taninaka

Pyeon

et al. 2011

An experimental technique based on an accelerator-beam trip or restart operation is proposed to determine the subcritical reactivity of an accelerator-driven system (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. A series of beam trip and restart experiments with 14 MeV neutrons were carried out in a thermal ADS of Kyoto University Critical Assembly (KUCA), to demonstrate the applicability of the proposed technique. The subcriticalities evaluated using neutron counters far from the DT target were consistent with those obtained in a previous pulsed neutron experiment. However, a counter placed close to the target significantly overestimated the subcriticality. The present technique is expected to be available for subcriritcality measurement at startup and shutdown of various ADSs.