TY - GEN
T1 - Kinetics of the high temperature oxygen exchange reaction on 238PuO2 powder
AU - Whiting, Christofer E.
AU - Du, Miting
AU - Felker, L. Kevin
AU - Wham, Robert M.
AU - Barklay, Chadwick D.
AU - Kramer, Daniel P.
PY - 2015
Y1 - 2015
N2 - Mechanisms and kinetics of the oxygen exchange reaction were studied on PuO2. Results indicate that the oxygen exchange behavior of PuO2 is quite complex. Exchange rates are influenced by three different mechanisms: a chemical reaction that is occurring within the bulk and not at the material surface, the surface mobility of active species/defects, and the actual exchange of surface adsorbed oxygen with lattice oxygen ions. Determining which mechanism dominates the overall exchange rate appears to be a complex function including at least temperature and specific surface area. The fastest exchange rate is controlled by an internal chemical reaction and can be obtained when the specific surface area of the PuO2 and exchange temperatures are high. The rate of this internal chemical reaction should be independent of most particle and atmospheric characteristics, including: specific surface area, oxygen partial pressure, total pressure, particle size, and grain size. As temperature and/or specific surface area decrease, eventually the surface mobility mechanism becomes slow enough to control the exchange rate. As temperature and/or specific surface area decrease further, the exchange rate will enter a regime where the surface mobility and surface exchange mechanisms become competitive, and eventually the surface exchange mechanism will become slow enough to completely dominate the exchange rate. These two surface mechanisms are observed to have a dependence on the specific surface area of the PuO2. Strong similarities are observed between the oxygen exchange behavior of CeO2 and PuO2. This suggests that CeO2 is a very good surrogate for PuO2 in this regard and means that the extensive oxygen exchange experiments performed on CeO2 can be used to predict the behavior of PuO2. Exposure of the PuO2 to high temperatures (≥ 600 oC) may cause a reduction in the specific surface area of the material due to initial phase sintering. Upon exposure to 1000 oC for ∼3 hours, the surface of the PuO2 appears to have stabilized enough that exposure to lower temperatures does not have a significant impact on the surface over the short term. Activation energies are obtained for the internal chemical reaction and the surface mobility reaction.
AB - Mechanisms and kinetics of the oxygen exchange reaction were studied on PuO2. Results indicate that the oxygen exchange behavior of PuO2 is quite complex. Exchange rates are influenced by three different mechanisms: a chemical reaction that is occurring within the bulk and not at the material surface, the surface mobility of active species/defects, and the actual exchange of surface adsorbed oxygen with lattice oxygen ions. Determining which mechanism dominates the overall exchange rate appears to be a complex function including at least temperature and specific surface area. The fastest exchange rate is controlled by an internal chemical reaction and can be obtained when the specific surface area of the PuO2 and exchange temperatures are high. The rate of this internal chemical reaction should be independent of most particle and atmospheric characteristics, including: specific surface area, oxygen partial pressure, total pressure, particle size, and grain size. As temperature and/or specific surface area decrease, eventually the surface mobility mechanism becomes slow enough to control the exchange rate. As temperature and/or specific surface area decrease further, the exchange rate will enter a regime where the surface mobility and surface exchange mechanisms become competitive, and eventually the surface exchange mechanism will become slow enough to completely dominate the exchange rate. These two surface mechanisms are observed to have a dependence on the specific surface area of the PuO2. Strong similarities are observed between the oxygen exchange behavior of CeO2 and PuO2. This suggests that CeO2 is a very good surrogate for PuO2 in this regard and means that the extensive oxygen exchange experiments performed on CeO2 can be used to predict the behavior of PuO2. Exposure of the PuO2 to high temperatures (≥ 600 oC) may cause a reduction in the specific surface area of the material due to initial phase sintering. Upon exposure to 1000 oC for ∼3 hours, the surface of the PuO2 appears to have stabilized enough that exposure to lower temperatures does not have a significant impact on the surface over the short term. Activation energies are obtained for the internal chemical reaction and the surface mobility reaction.
KW - Kinetics
KW - Oxygen exchange
KW - Plutonium (IV) oxide
KW - Reaction mechanisms
UR - http://www.scopus.com/inward/record.url?scp=85027691267&partnerID=8YFLogxK
M3 - Conference contribution
AN - SCOPUS:85027691267
T3 - Nuclear and Emerging Technologies for Space, NETS 2015
SP - 152
EP - 159
BT - Nuclear and Emerging Technologies for Space, NETS 2015
PB - American Nuclear Society
T2 - 2015 Nuclear and Emerging Technologies for Space, NETS 2015
Y2 - 23 February 2015 through 26 February 2015
ER -