Air oxidation of yttrium hydride as a high temperature moderator for thermal neutron spectrum fission reactors

K. Kane; X. Hu; P. Stack; P. Mouche; B. Brigham; E. Sooby; B. Pint

doi:10.1016/j.jnucmat.2021.153166

Air oxidation of yttrium hydride as a high temperature moderator for thermal neutron spectrum fission reactors

K. Kane, X. Hu, P. Stack, P. Mouche, B. Brigham, E. Sooby, B. Pint

Materials Science and Technology Div

Research output: Contribution to journal › Article › peer-review

11 Scopus citations

Abstract

Yttrium hydride (YH_x) is an attractive moderator material for thermal neutron spectrum fission reactors requiring a small reactor core volume and has been selected as the neutron moderator for the Transformational Challenge Reactor (TCR), an advanced gas-cooled microreactor. Before YH_x can be used in this application, it is important to understand the material response to off-normal conditions. In the present study, 550–650 °C isothermal dry air oxidation was performed to simulate a depressurized loss of force circulation (DLOFC) event. The oxidation was performed using thermogravimetric analysis (TGA) on bulk crack-free YH_x coupons. Oxidation studies were also performed on Y coupons to elucidate the impact of H on oxidation. Both the chemistry and distribution of processing impurities were found to strongly affect oxidization behavior on a batch-to-batch basis. Regardless of batch, YH_x oxidized at a significantly lower rate than Y at all temperatures, and the lower rate was directly correlated with increased hydride content. Metallic Y exhibited complex exponential kinetics, whereas YH_x also exhibited complex kinetics but gained considerably less mass. According to literature reports on protonic and native-ion conductivities of Y₂O₃ and mass spectrometry analysis of gaseous reaction products formed during the oxidation of YH_x, a mechanism for the reduced oxidation rate of yttrium hydride is suggested.

Original language	English
Article number	153166
Journal	Journal of Nuclear Materials
Volume	556
DOIs	https://doi.org/10.1016/j.jnucmat.2021.153166
State	Published - Dec 1 2021

Funding

The authors would like to thank Matt Kurley III and Truls Norby for discussing results and providing valuable insight during analysis, and also to Cory Parker and Dino Sulejmanovic for providing technical review. Much thanks is given to Rose Raney, who was a technical editor on the manuscript, and Solaire O. Astora and P.T. Sun for their helpful incandescence during the long and arduous journey. This research was sponsored by the Transformational Challenge Reactor Program of the US Department of Energy, Office of Nuclear Energy. Support for the UTSA faculty participating in this work is funded by a Nuclear Regulatory Commission Faculty Development Grant, award number 31310018M0046.

Keywords

High temperature oxidation
Metal hydride
Transformational challenge reactor
Yttrium hydride
moderator
yttria

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title = "Air oxidation of yttrium hydride as a high temperature moderator for thermal neutron spectrum fission reactors",

abstract = "Yttrium hydride (YHx) is an attractive moderator material for thermal neutron spectrum fission reactors requiring a small reactor core volume and has been selected as the neutron moderator for the Transformational Challenge Reactor (TCR), an advanced gas-cooled microreactor. Before YHx can be used in this application, it is important to understand the material response to off-normal conditions. In the present study, 550–650 °C isothermal dry air oxidation was performed to simulate a depressurized loss of force circulation (DLOFC) event. The oxidation was performed using thermogravimetric analysis (TGA) on bulk crack-free YHx coupons. Oxidation studies were also performed on Y coupons to elucidate the impact of H on oxidation. Both the chemistry and distribution of processing impurities were found to strongly affect oxidization behavior on a batch-to-batch basis. Regardless of batch, YHx oxidized at a significantly lower rate than Y at all temperatures, and the lower rate was directly correlated with increased hydride content. Metallic Y exhibited complex exponential kinetics, whereas YHx also exhibited complex kinetics but gained considerably less mass. According to literature reports on protonic and native-ion conductivities of Y2O3 and mass spectrometry analysis of gaseous reaction products formed during the oxidation of YHx, a mechanism for the reduced oxidation rate of yttrium hydride is suggested.",

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author = "K. Kane and X. Hu and P. Stack and P. Mouche and B. Brigham and E. Sooby and B. Pint",

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AU - Kane, K.

AU - Hu, X.

AU - Stack, P.

AU - Mouche, P.

AU - Brigham, B.

AU - Sooby, E.

AU - Pint, B.

PY - 2021/12/1

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N2 - Yttrium hydride (YHx) is an attractive moderator material for thermal neutron spectrum fission reactors requiring a small reactor core volume and has been selected as the neutron moderator for the Transformational Challenge Reactor (TCR), an advanced gas-cooled microreactor. Before YHx can be used in this application, it is important to understand the material response to off-normal conditions. In the present study, 550–650 °C isothermal dry air oxidation was performed to simulate a depressurized loss of force circulation (DLOFC) event. The oxidation was performed using thermogravimetric analysis (TGA) on bulk crack-free YHx coupons. Oxidation studies were also performed on Y coupons to elucidate the impact of H on oxidation. Both the chemistry and distribution of processing impurities were found to strongly affect oxidization behavior on a batch-to-batch basis. Regardless of batch, YHx oxidized at a significantly lower rate than Y at all temperatures, and the lower rate was directly correlated with increased hydride content. Metallic Y exhibited complex exponential kinetics, whereas YHx also exhibited complex kinetics but gained considerably less mass. According to literature reports on protonic and native-ion conductivities of Y2O3 and mass spectrometry analysis of gaseous reaction products formed during the oxidation of YHx, a mechanism for the reduced oxidation rate of yttrium hydride is suggested.

AB - Yttrium hydride (YHx) is an attractive moderator material for thermal neutron spectrum fission reactors requiring a small reactor core volume and has been selected as the neutron moderator for the Transformational Challenge Reactor (TCR), an advanced gas-cooled microreactor. Before YHx can be used in this application, it is important to understand the material response to off-normal conditions. In the present study, 550–650 °C isothermal dry air oxidation was performed to simulate a depressurized loss of force circulation (DLOFC) event. The oxidation was performed using thermogravimetric analysis (TGA) on bulk crack-free YHx coupons. Oxidation studies were also performed on Y coupons to elucidate the impact of H on oxidation. Both the chemistry and distribution of processing impurities were found to strongly affect oxidization behavior on a batch-to-batch basis. Regardless of batch, YHx oxidized at a significantly lower rate than Y at all temperatures, and the lower rate was directly correlated with increased hydride content. Metallic Y exhibited complex exponential kinetics, whereas YHx also exhibited complex kinetics but gained considerably less mass. According to literature reports on protonic and native-ion conductivities of Y2O3 and mass spectrometry analysis of gaseous reaction products formed during the oxidation of YHx, a mechanism for the reduced oxidation rate of yttrium hydride is suggested.

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KW - Metal hydride

KW - Transformational challenge reactor

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Air oxidation of yttrium hydride as a high temperature moderator for thermal neutron spectrum fission reactors

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