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Title: Characterization of the kinetics of NF 3-fluorination of NpO 2

Abstract

The exploitation of selected actinide and fission product fluoride volatilities has long been considered as a potentially attractive compact method for recycling used nuclear fuels to avoid generating the large volumes of radioactive waste arising from aqueous reprocessing . The most developed process uses the aggressive and hazardous fluorinating agents hydrogen fluoride (HF) and/or molecular fluorine (F 2) at high temperatures to volatilize the greatest fraction of the used nuclear fuel into a single gas stream. The volatilized fluorides are subsequently separated using a series of fractionation and condensation columns to recover the valuable fuel constituents and fission products. In pursuit of a safer and less complicated approach, we investigated an alternative fluoride volatility-based process using the less hazardous fluorinating agent nitrogen trifluoride (NF 3) and leveraging its less aggressive nature to selectively evolve fission product and actinide fluorides from the solid phase based on their reaction temperatures into a single recycle stream. In this approach, successive isothermal treatments using NF 3 will first evolve the more thermally susceptible used nuclear fuel constituents leaving the other constituents in the residual solids until subsequent isothermal temperature treatments cause these others to volatilize. During investigation of this process, individual neat used fuelmore » components were treated with isothermal NF 3 in an attempt to characterize the kinetics of each fluorination reaction to provide input into the design of a new volatile fluoride separations approach. In these directed investigations, complex behavior was observed between NF 3 and certain solid reactants such as the actinide oxides of uranium, plutonium, and neptunium. Given the similar thermal reaction susceptibilities of neptunium oxide (NpO 2) and uranium dioxide (UO 2) and the importance of Np and U, we initially focused our efforts on determining the reaction kinetic parameters for NpO 2. Characterizing the NF3 fluorination of NpO 2 using established models for gas-solid reactions [16] proved unsuccessful so we developed a series of successive fundamental reaction mechanisms to characterize the observed successive fluorination reactions leading to production of the volatile neptunium hexafluoride (NpF 6).« less

Authors:
ORCiD logo [1];  [1];  [1]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1236917
Report Number(s):
PNNL-SA-113410
Journal ID: ISSN 2158-3226
Grant/Contract Number:  
AC05-76RL01830
Resource Type:
Accepted Manuscript
Journal Name:
AIP Advances
Additional Journal Information:
Journal Volume: 5; Journal Issue: 12; Journal ID: ISSN 2158-3226
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Casella, Andrew M., Scheele, Randall D., and McNamara, Bruce K. Characterization of the kinetics of NF3-fluorination of NpO2. United States: N. p., 2015. Web. doi:10.1063/1.4939143.
Casella, Andrew M., Scheele, Randall D., & McNamara, Bruce K. Characterization of the kinetics of NF3-fluorination of NpO2. United States. doi:10.1063/1.4939143.
Casella, Andrew M., Scheele, Randall D., and McNamara, Bruce K. Wed . "Characterization of the kinetics of NF3-fluorination of NpO2". United States. doi:10.1063/1.4939143. https://www.osti.gov/servlets/purl/1236917.
@article{osti_1236917,
title = {Characterization of the kinetics of NF3-fluorination of NpO2},
author = {Casella, Andrew M. and Scheele, Randall D. and McNamara, Bruce K.},
abstractNote = {The exploitation of selected actinide and fission product fluoride volatilities has long been considered as a potentially attractive compact method for recycling used nuclear fuels to avoid generating the large volumes of radioactive waste arising from aqueous reprocessing . The most developed process uses the aggressive and hazardous fluorinating agents hydrogen fluoride (HF) and/or molecular fluorine (F2) at high temperatures to volatilize the greatest fraction of the used nuclear fuel into a single gas stream. The volatilized fluorides are subsequently separated using a series of fractionation and condensation columns to recover the valuable fuel constituents and fission products. In pursuit of a safer and less complicated approach, we investigated an alternative fluoride volatility-based process using the less hazardous fluorinating agent nitrogen trifluoride (NF3) and leveraging its less aggressive nature to selectively evolve fission product and actinide fluorides from the solid phase based on their reaction temperatures into a single recycle stream. In this approach, successive isothermal treatments using NF3 will first evolve the more thermally susceptible used nuclear fuel constituents leaving the other constituents in the residual solids until subsequent isothermal temperature treatments cause these others to volatilize. During investigation of this process, individual neat used fuel components were treated with isothermal NF3 in an attempt to characterize the kinetics of each fluorination reaction to provide input into the design of a new volatile fluoride separations approach. In these directed investigations, complex behavior was observed between NF3 and certain solid reactants such as the actinide oxides of uranium, plutonium, and neptunium. Given the similar thermal reaction susceptibilities of neptunium oxide (NpO2) and uranium dioxide (UO2) and the importance of Np and U, we initially focused our efforts on determining the reaction kinetic parameters for NpO2. Characterizing the NF3 fluorination of NpO2 using established models for gas-solid reactions [16] proved unsuccessful so we developed a series of successive fundamental reaction mechanisms to characterize the observed successive fluorination reactions leading to production of the volatile neptunium hexafluoride (NpF6).},
doi = {10.1063/1.4939143},
journal = {AIP Advances},
number = 12,
volume = 5,
place = {United States},
year = {2015},
month = {12}
}

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Works referenced in this record:

Fluoride volatility method for reprocessing of LWR and FR fuels
journal, January 2009


New reprocessing system for spent nuclear reactor fuel using fluoride volatility method
journal, January 2009


Fluorex reprocessing system for the thermal reactors cycle and future thermal/fast reactors (coexistence) cycle
journal, January 2005

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  • Progress in Nuclear Energy, Vol. 47, Issue 1-4, p. 380-388
  • DOI: 10.1016/j.pnucene.2005.05.037