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Title: Conceptual moderator studies for the Spallation Neutron Source short-pulse second target station

Abstract

We identified candidate moderator configurations for a short-pulse second target station (STS) at the Oak Ridge National Laboratory Spallation Neutron Source (SNS) using a global optimizer framework built around the MCNPX particle transport code. Neutron brightness metrics were selected as the figure-of-merit. We assumed that STS would use one out of six proton pulses produced by an SNS accelerator upgraded to operate at 1.3 GeV proton energy, 2.8 MW power and 60 Hz repetition rate. The simulations indicate that the peak brightness can be increased by a factor of 5 and 2.5 on a per proton pulse basis compared to the SNS first target station for both coupled and decoupled para-hydrogen moderators, respectively. Additional increases by factors of 3 and 2 were demonstrated for coupled and decoupled moderators, respectively, by reducing the area of neutron emission from 100 × 100 mm2 to 20 × 20 mm2. Furthermore, this increase in brightness has the potential to translate to an increase of beam intensity at the instruments’ sample positions even though the total neutron emission of the smaller moderator is less than that of the larger. This is especially true for instruments with small samples (beam dimensions). The increased fluxes in themore » STS moderators come at accelerated poison and de-coupler burnout and higher radiation-induced material damage rates per unit power, which overall translate into lower moderator lifetimes. Our first effort decoupled group moderators into a cluster collectively positioning them at the peak neutron production zone in the target and having a three-port neutron emission scheme that complements that of a cylindrical coupled moderator.« less

Authors:
ORCiD logo [1];  [1]; ORCiD logo [1];  [1]; ORCiD logo [1];  [1]
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  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Instrument and Source Division
Publication Date:
Research Org.:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1326471
Alternate Identifier(s):
OSTI ID: 1420629
Grant/Contract Number:  
AC05-00OR22725; 7540
Resource Type:
Accepted Manuscript
Journal Name:
Review of Scientific Instruments
Additional Journal Information:
Journal Volume: 87; Journal Issue: 6; Journal ID: ISSN 0034-6748
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY

Citation Formats

Gallmeier, F. X., Lu, W., Riemer, B. W., Zhao, J. K., Herwig, K. W., and Robertson, J. L. Conceptual moderator studies for the Spallation Neutron Source short-pulse second target station. United States: N. p., 2016. Web. doi:10.1063/1.4953612.
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Gallmeier, F. X., Lu, W., Riemer, B. W., Zhao, J. K., Herwig, K. W., & Robertson, J. L. Conceptual moderator studies for the Spallation Neutron Source short-pulse second target station. United States. https://doi.org/10.1063/1.4953612
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Gallmeier, F. X., Lu, W., Riemer, B. W., Zhao, J. K., Herwig, K. W., and Robertson, J. L. Tue . "Conceptual moderator studies for the Spallation Neutron Source short-pulse second target station". United States. https://doi.org/10.1063/1.4953612. https://www.osti.gov/servlets/purl/1326471.
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@article{osti_1326471,
title = {Conceptual moderator studies for the Spallation Neutron Source short-pulse second target station},
author = {Gallmeier, F. X. and Lu, W. and Riemer, B. W. and Zhao, J. K. and Herwig, K. W. and Robertson, J. L.},
abstractNote = {We identified candidate moderator configurations for a short-pulse second target station (STS) at the Oak Ridge National Laboratory Spallation Neutron Source (SNS) using a global optimizer framework built around the MCNPX particle transport code. Neutron brightness metrics were selected as the figure-of-merit. We assumed that STS would use one out of six proton pulses produced by an SNS accelerator upgraded to operate at 1.3 GeV proton energy, 2.8 MW power and 60 Hz repetition rate. The simulations indicate that the peak brightness can be increased by a factor of 5 and 2.5 on a per proton pulse basis compared to the SNS first target station for both coupled and decoupled para-hydrogen moderators, respectively. Additional increases by factors of 3 and 2 were demonstrated for coupled and decoupled moderators, respectively, by reducing the area of neutron emission from 100 × 100 mm2 to 20 × 20 mm2. Furthermore, this increase in brightness has the potential to translate to an increase of beam intensity at the instruments’ sample positions even though the total neutron emission of the smaller moderator is less than that of the larger. This is especially true for instruments with small samples (beam dimensions). The increased fluxes in the STS moderators come at accelerated poison and de-coupler burnout and higher radiation-induced material damage rates per unit power, which overall translate into lower moderator lifetimes. Our first effort decoupled group moderators into a cluster collectively positioning them at the peak neutron production zone in the target and having a three-port neutron emission scheme that complements that of a cylindrical coupled moderator.},
doi = {10.1063/1.4953612},
journal = {Review of Scientific Instruments},
number = 6,
volume = 87,
place = {United States},
year = {Tue Jun 14 00:00:00 EDT 2016},
month = {Tue Jun 14 00:00:00 EDT 2016}
}
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https://doi.org/10.1063/1.4953612
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Works referenced in this record:

The extended Q -range small-angle neutron scattering diffractometer at the SNS
journal, July 2010

Unperturbed moderator brightness in pulsed neutron sources
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Irradiation effects in liquid methane used as a neutron moderator
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journal, December 2011

Neutronics of pulsed spallation neutron sources
journal, February 2003

Moderator poison design and burn-up calculations at the SNS
journal, June 2008

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