TEM examination of phases formed between U–Pu–Zr fuel and Fe

Abstract

Exposure to high temperatures and irradiation results in interaction and interdiffusion between fuel and cladding constituents that can lead to formation of undesirable brittle or low-melting point phases. A diffusion couple study has been conducted to understand fuel-cladding interaction occurring between U-22Pu-4Zr (in wt%) fuel and pure Fe at elevated temperatures. The phases formed within fuel cladding chemical interaction (FCCI) layer have been characterized in the transmission electron microscope (TEM). The phases formed within FCCI layer have been identified as Fe 2 U (Fd-3m), FeU 6 (I4/mcm), Fe 2 Zr (Fd-3m), FeZr 2 (I4/mcm), Fe 2 Pu (Fd-3m), UZr 2 (P6/mmm), β-Zr (Im-3m), and ZrO 2 (Fm-3m).

Fuel-Cladding Interaction Between U-Pu-Zr Fuel and Fe

“…The Zr-rich precipitates, stabilized by dissolved impurities such as N, O, and C, have been observed in a variety of transmutation fuels. [14][15][16][17][18][19][20] In previous studies, these Zr-rich precipitates were assumed to be a-Zr that formed during alloy preparation because of the interstitial impurities present in the feedstock. [14] Our previous investigation of the U-Pu-Zr fuel showed the formation of Zr precipitates in the vicinity of the specimen surface.…”

“…[14] Our previous investigation of the U-Pu-Zr fuel showed the formation of Zr precipitates in the vicinity of the specimen surface. [20] It is believed that migration of zirconium to the surface of the sample during annealing leads to the separation of Zr phase from the matrix and formation of a thin layer on the surface of the fuel. [15] Formation of this oxygenated surface upon exposure of the sample to air combined with migration of Zr toward the oxygen upon heating of the specimen results in formation of the a-Zr.…”

“…The summary of all observed phases is provided in Table I. Our previous investigation of the phases and microstructure in U-Pu-Zr fuel, with compositions [20] In the investigation of U-23Pu-9Zr fuel, the fuel matrix consisted of d-UZr 2 , b-Pu, and (U, Zr)ht phases. [20] Upon annealing of the fuel in contact with the cladding, d-UZr 2 and (U, Zr)ht phases disappear and only b-Pu phase remains.…”

“…Our previous investigation of the phases and microstructure in U-Pu-Zr fuel, with compositions [20] In the investigation of U-23Pu-9Zr fuel, the fuel matrix consisted of d-UZr 2 , b-Pu, and (U, Zr)ht phases. [20] Upon annealing of the fuel in contact with the cladding, d-UZr 2 and (U, Zr)ht phases disappear and only b-Pu phase remains. However, b-Pu no longer comprises a majority of the fuel matrix but is present in the form of more or less globular precipitates surrounded by the Fe 2 Zr phase ( Figure 7).…”

Atomic-scale modeling of twinning disconnections in zirconium

“…This potential, developed for bulk hcp Zr with a special emphasis on stacking faults controlling dislocation dissociation, has already been shown to give a reliable description of Zr plasticity. [22][23][24][25][26][27][28] Ab initio calculations were performed with the VASP code, 29 using the Perdew-Becke-Erzenhof 30 parameterization for the GGA exchange and correlation functional. The interactions between the core and outer electrons are modeled through the projector augmented wave approximation, considering valence (5s 2 4d 2 ) and semicore electrons (4s 2 4p 6 ) in the outer shell.…”