Reactor performance and safety characteristics of ThN-UN fuel concepts in a PWR

Jacob P. Gorton; Benjamin S. Collins; Andrew T. Nelson; Nicholas R. Brown

doi:10.1016/j.nucengdes.2019.110317

Reactor performance and safety characteristics of ThN-UN fuel concepts in a PWR

Jacob P. Gorton, Benjamin S. Collins, Andrew T. Nelson, Nicholas R. Brown

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20 Scopus citations

Abstract

The reactor performance and safety characteristics of mixed thorium mononitride (ThN) and uranium mononitride (UN) fuels in a pressurized water reactor (PWR) are investigated to discern the potential nonproliferation, waste, and accident tolerance benefits provided by this fuel form. This paper presents results from an initial screening of mixed ThN-UN fuels in normal PWR operating conditions and compares their reactor performance to UO₂ in terms of fuel cycle length, reactivity coefficients, and thermal safety margin. ThN has been shown to have a significantly greater thermal conductivity than UO₂ and UN. Admixture with a UN phase is required because thorium initially contains no fissile isotopes. Results from this study show that ThN-UN mixtures exist that can match the cycle length of a UO₂-fueled reactor by using ²³⁵U enrichments greater than 5% but less than 20% in the UN phase. Reactivity coefficients were calculated for UO₂, UN, and ThN-UN mixtures, and it was found that the fuel temperature and moderator temperature coefficients of the nitride-based fuels fall within the acceptable limits specified by the AP1000 Design Control Document. Reduced soluble boron and control rod worth for these fuel forms indicates that the shutdown margin may not be sufficient, and design changes to the control systems may need to be considered. The neutronic impact of ¹⁵N enrichment on reactivity coefficients is also included. Due to the greatly enhanced thermal conductivity of the nitride-based fuels, the UN and ThN-UN fuels provide additional margin to fuel melting temperature relative to UO₂.

Original language	English
Article number	110317
Journal	Nuclear Engineering and Design
Volume	355
DOIs	https://doi.org/10.1016/j.nucengdes.2019.110317
State	Published - Dec 15 2019

Funding

This work was funded by the U.S. Department of Energy Office of Nuclear Energy Advanced Fuels Campaign. This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). This work was funded by the U.S. Department of Energy Office of Nuclear Energy Advanced Fuels Campaign. This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan).

Funders	Funder number
DOE Public Access Plan
U.S. Department of Energy Office of Nuclear Energy Advanced Fuels Campaign	DE-AC05-00OR22725
US Department of Energy
U.S. Department of Energy

Keywords

Accident tolerant fuel
Homologous temperature
Safety margin
Thorium nitride
Uranium nitride

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10.1016/j.nucengdes.2019.110317

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title = "Reactor performance and safety characteristics of ThN-UN fuel concepts in a PWR",

abstract = "The reactor performance and safety characteristics of mixed thorium mononitride (ThN) and uranium mononitride (UN) fuels in a pressurized water reactor (PWR) are investigated to discern the potential nonproliferation, waste, and accident tolerance benefits provided by this fuel form. This paper presents results from an initial screening of mixed ThN-UN fuels in normal PWR operating conditions and compares their reactor performance to UO2 in terms of fuel cycle length, reactivity coefficients, and thermal safety margin. ThN has been shown to have a significantly greater thermal conductivity than UO2 and UN. Admixture with a UN phase is required because thorium initially contains no fissile isotopes. Results from this study show that ThN-UN mixtures exist that can match the cycle length of a UO2-fueled reactor by using 235U enrichments greater than 5% but less than 20% in the UN phase. Reactivity coefficients were calculated for UO2, UN, and ThN-UN mixtures, and it was found that the fuel temperature and moderator temperature coefficients of the nitride-based fuels fall within the acceptable limits specified by the AP1000 Design Control Document. Reduced soluble boron and control rod worth for these fuel forms indicates that the shutdown margin may not be sufficient, and design changes to the control systems may need to be considered. The neutronic impact of 15N enrichment on reactivity coefficients is also included. Due to the greatly enhanced thermal conductivity of the nitride-based fuels, the UN and ThN-UN fuels provide additional margin to fuel melting temperature relative to UO2.",

keywords = "Accident tolerant fuel, Homologous temperature, Safety margin, Thorium nitride, Uranium nitride",

author = "Gorton, {Jacob P.} and Collins, {Benjamin S.} and Nelson, {Andrew T.} and Brown, {Nicholas R.}",

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AB - The reactor performance and safety characteristics of mixed thorium mononitride (ThN) and uranium mononitride (UN) fuels in a pressurized water reactor (PWR) are investigated to discern the potential nonproliferation, waste, and accident tolerance benefits provided by this fuel form. This paper presents results from an initial screening of mixed ThN-UN fuels in normal PWR operating conditions and compares their reactor performance to UO2 in terms of fuel cycle length, reactivity coefficients, and thermal safety margin. ThN has been shown to have a significantly greater thermal conductivity than UO2 and UN. Admixture with a UN phase is required because thorium initially contains no fissile isotopes. Results from this study show that ThN-UN mixtures exist that can match the cycle length of a UO2-fueled reactor by using 235U enrichments greater than 5% but less than 20% in the UN phase. Reactivity coefficients were calculated for UO2, UN, and ThN-UN mixtures, and it was found that the fuel temperature and moderator temperature coefficients of the nitride-based fuels fall within the acceptable limits specified by the AP1000 Design Control Document. Reduced soluble boron and control rod worth for these fuel forms indicates that the shutdown margin may not be sufficient, and design changes to the control systems may need to be considered. The neutronic impact of 15N enrichment on reactivity coefficients is also included. Due to the greatly enhanced thermal conductivity of the nitride-based fuels, the UN and ThN-UN fuels provide additional margin to fuel melting temperature relative to UO2.

KW - Accident tolerant fuel

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Reactor performance and safety characteristics of ThN-UN fuel concepts in a PWR

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Keywords

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