Improving variance convergence rate in monte carlo eigenvalue simulations via delayed neutrons

Miao, Jilang; Forget, Benoit; Smith, Kord

doi:10.1016/j.anucene.2020.107376

Cited by 7 publications

(3 citation statements)

References 22 publications

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“…The persistence of stochastic effects at operating conditions might instead screen this state of the reactor and shall therefore be avoided. In this respect, the appearance of fission-induced correlations in nuclear systems has been extensively investigated [15,16,17,18]; furthermore, neutron clustering has drawn much attention in recent years, with a special emphasis on numerical (Monte Carlo) simulations [13,14,19,20,21,22,23]. Quantifying and characterizing fluctuations and spatial correlations in a low-power reactor has a theoretical and practical interest: the experimental validation of theoretical fluctuations and correlations models at low power would allow to scale them at higher powers, numericaly far from reach.…”

Section: Introductionmentioning

confidence: 99%

Patchy snapshots of nuclear chain reactions

Dumonteil¹,

Bahran

Cutler

et al. 2020

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Stochastic fluctuations of the neutron population within a nuclear reactor are typically prevented by operating the core at a sufficiently high power. This regime, where the evolution of the neutron density is essentially deterministic, is key for automatic protection and safety systems to safely detect unwanted power excursions during an accident, and to rapidly initiate a reactor trip procedure in case it is needed. Recent works, supported by numerical simulations, have however reported that, for large reactors, the branching nature of the fission reactions might induce strongly non-Poissonian patterns in the neutron spatial distribution, and that stochastic fluctuations might still persist at reactor powers close to operating conditions (startup phase). An international program conducted by LANL, IRSN and CEA was therefore setup to experimentally detect and characterize such fluctuations and correlations. An experiment took place in 2017 at the Reactor Critical Facility (RCF) of the Rensselaer Polytechnic Institute (USA). In this paper we will report the main findings of this experimental program, supported by stochastic models and by the development of a dedicated high-fidelity Monte Carlo simulation code. We will in particular describe and explain the strong patchiness in neutron power distributions measured at the RCF, as well as a peculiar 'blinking' behavior of the core, and discuss the consequences of these findings on nuclear safety.

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Section: Introductionmentioning

confidence: 99%

Patchy snapshots of nuclear chain reactions

Dumonteil¹,

Bahran

Cutler

et al. 2020

View full text Add to dashboard Cite

show abstract

“…The persistence of stochastic effects at operating conditions (in particular during the startup phase) might instead screen this state of the reactor and shall therefore be avoided. In this respect, the appearance of fission-induced correlations in nuclear systems has been extensively investigated [15,16,17,18]; furthermore, neutron clustering has drawn much attention in recent years, with a special emphasis on numerical (Monte Carlo) simulations [13,14,19,20,21,22,23]. Quantifying and characterizing fluctuations and spatial correlations in a low-power reactor has a theoretical and practical interest: the experimental validation of theoretical fluctuations and correlations models at low power would allow to scale them at higher powers, numericaly far from reach.…”

Section: Introductionmentioning

confidence: 99%

Patchy nuclear chain reactions

Dumonteil¹,

Bahran²,

Cutler³

et al. 2020

Preprint

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Stochastic fluctuations of the neutron population within a nuclear reactor are typically prevented by operating the core at a sufficient power, since a deterministic behavior of the neutron population is required by automatic safety systems to detect unwanted power excursions. Recent works however pointed out that, under specific circumstances, non-Poissonian patterns could affect neutron spatial distributions. This motivated an international program to experimentally detect and characterize such fluctuations and correlations, which took place in 2017 at the Rensselaer Polytechnic Institute Reactor Critical Facility. The main findings of this program will indeed unveil patchiness in snapshots of neutron spatial distributions -obtained with a dedicated numerical twin of the reactor-that support this first experimental characterization of the 'neutron clustering' phenomenon, while a stochastic model based on reaction-diffusion processes and branching random walks will reveal the key role played by the reactor intrinsic sources in understanding neutron spatial correlations.

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“…Some of the numerical simulations reported strong non-Poissonian patterns affecting neutron spatial distributions in decoupled nuclear systems, where the system size is larger than the typical length scale travelled by the neutrons. In particular, the occurrence of a spontaneous clustering of the neutron population has drawn much attention in recent years [7][8][9][10][11][12][13] and questions were raised as to whether this phenomenon was a simulation artifact or if it could be experimentally detected. It is known that a collection of independent particles that move, reproduce, and die may undergo wild fluctuations at the local and global scales inducing a characteristic patchiness in the spatial distribution of the individuals observed in the context of life sciences, including the spread of epidemics [14][15][16] , the growth of bacteria on Petri dishes 17,18 , the dynamics of ecological communities 19,20 , and the mutation propagation of genes 21,22 .…”

mentioning

confidence: 99%

Patchy nuclear chain reactions

et al. 2021

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Stochastic fluctuations of the neutron population within a nuclear reactor are typically prevented by operating the core at a sufficient power, since a deterministic (i.e., exactly predictable) behavior of the neutron population is required by automatic safety systems to detect unwanted power excursions. In order to characterize the reactor operating conditions at which the fluctuations vanish, an experiment was designed and took place in 2017 at the Rensselaer Polytechnic Institute Reactor Critical Facility. This experiment however revealed persisting fluctuations and striking patchy spatial patterns in neutron spatial distributions. Here we report these experimental findings, interpret them by a stochastic modeling based on branching random walks, and extend them using a “numerical twin” of the reactor core. Consequences on nuclear safety will be discussed.

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Improving variance convergence rate in monte carlo eigenvalue simulations via delayed neutrons

Cited by 7 publications

References 22 publications

Patchy snapshots of nuclear chain reactions

Patchy snapshots of nuclear chain reactions

Patchy nuclear chain reactions

Patchy nuclear chain reactions

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