Analysis of the Temporal Response of Coupled Asymmetrical ZeroPower Subcritical Bare Metal Reactor Systems
Abstract
The behavior of symmetrical coupledcore systems has been extensively studied, yet there is a dearth of research on asymmetrical systems due to the increased complexity of the analysis of such systems. In this research, the multipoint kinetics method is applied to asymmetrical zeropower, subcritical, bare metal reactor systems. Existing research on asymmetrical reactor systems assumes symmetry in the neutronic coupling; however, it will be shown that this cannot always be assumed. Deep subcriticality adds another layer of complexity and requires modification of the multipoint kinetics equations to account for the effect of the external neutron source. A modified set of multipoint kinetics equations is derived with this in mind. Subsequently, the Rossialpha equations are derived for a tworegion asymmetrical reactor system. The predictive capabilities of the radiation transport code MCNP6 for neutron noise experiments are shown in a comparison to the results of a series of Rossialpha measurements performed by J. Mihalczo utilizing a coupled set of symmetrical bare highlyenriched uranium (HEU) cylinders. The ptrac option within MCNP6 can generate timetagged counts in a cell (listmode data). The listmode data can then be processed similarly to measured data to obtain values for system parameters such as the dual prompt neutronmore »
 Authors:
 Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
 Publication Date:
 Research Org.:
 Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
 Sponsoring Org.:
 USDOE Office of Environment, Health, Safety and Security (AU). Office of Nuclear Safety (AU30)
 OSTI Identifier:
 1367792
 Report Number(s):
 LAUR1725007
 DOE Contract Number:
 AC5206NA25396
 Resource Type:
 Technical Report
 Country of Publication:
 United States
 Language:
 English
 Subject:
 21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
Citation Formats
Klain, Kimberly L. Analysis of the Temporal Response of Coupled Asymmetrical ZeroPower Subcritical Bare Metal Reactor Systems. United States: N. p., 2017.
Web. doi:10.2172/1367792.
Klain, Kimberly L. Analysis of the Temporal Response of Coupled Asymmetrical ZeroPower Subcritical Bare Metal Reactor Systems. United States. doi:10.2172/1367792.
Klain, Kimberly L. 2017.
"Analysis of the Temporal Response of Coupled Asymmetrical ZeroPower Subcritical Bare Metal Reactor Systems". United States.
doi:10.2172/1367792. https://www.osti.gov/servlets/purl/1367792.
@article{osti_1367792,
title = {Analysis of the Temporal Response of Coupled Asymmetrical ZeroPower Subcritical Bare Metal Reactor Systems},
author = {Klain, Kimberly L.},
abstractNote = {The behavior of symmetrical coupledcore systems has been extensively studied, yet there is a dearth of research on asymmetrical systems due to the increased complexity of the analysis of such systems. In this research, the multipoint kinetics method is applied to asymmetrical zeropower, subcritical, bare metal reactor systems. Existing research on asymmetrical reactor systems assumes symmetry in the neutronic coupling; however, it will be shown that this cannot always be assumed. Deep subcriticality adds another layer of complexity and requires modification of the multipoint kinetics equations to account for the effect of the external neutron source. A modified set of multipoint kinetics equations is derived with this in mind. Subsequently, the Rossialpha equations are derived for a tworegion asymmetrical reactor system. The predictive capabilities of the radiation transport code MCNP6 for neutron noise experiments are shown in a comparison to the results of a series of Rossialpha measurements performed by J. Mihalczo utilizing a coupled set of symmetrical bare highlyenriched uranium (HEU) cylinders. The ptrac option within MCNP6 can generate timetagged counts in a cell (listmode data). The listmode data can then be processed similarly to measured data to obtain values for system parameters such as the dual prompt neutron decay constants observable in a coupled system. The results from the ptrac simulations agree well with the historical measured values. A series of case studies are conducted to study the effects of geometrical asymmetry in the coupling between two bare metal HEU cylinders. While the coupling behavior of symmetrical systems has been reported on extensively, that of asymmetrical systems remains sparse. In particular, it appears that there has been no previous research in obtaining the coupling time constants for asymmetricallycoupled systems. The difficulty in observing such systems is due in part to the inability to determine the individual coupling coefficients from measurement: unlike the symmetrical cases, only the product of the values can be obtained. A method is proposed utilizing MCNP6 tally ratios to separate the coupling coefficients for such systems. This work provides insight into the behavior of asymmetricallycoupled systems as the separation distance between the two cores is changed and also as the asymmetry is increased. As the asymmetry increases, both the slower and the faster observable prompt neutron decay constants increase in magnitude. The coupling time constants are determined from the measured decay constants. As the separation distance increases, both coupling coefficients decrease as expected. Based on these findings, an effective computational method utilizing MCNP6 and the Rossialpha technique can be applied to the prediction of asymmetrical coupled system measurements.},
doi = {10.2172/1367792},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 6
}

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