Performance of U-Pu-Zr fuel cast into zirconium molds

Abstract

U-3Zr and U-20.5Pu-3Zrwere injectioncast into Zr tubes, or sheaths, rather than into quartz molds and clad in 316SS. These elements and standard-castU-IOZr and U-19Pu-10Zr elements were irradiatedin EBR-II to 2 at.% and removed for interim examination. Measurments of axial growth at indicate that the Zr-sheathed elements exhibited significantlyless axial elongation than the standard-castelements (1.3 to 1.8 % versus 4.9 to 8.1 %). Fuel material extruded through the ends of the Zr sheaths, allowing the low-Zr fuel to contact the cladding in some cases. Transverse metallographic sections reveal cracks in the Zr sheath through which fuel extruded and contacted cladding. The sheath is not a sufficient barrier between fuel and cladding to reduce FCCl, and any adverse effects due to increasedFCCI will be evident as the elements attain higher burnup.

A US perspective on fast reactor fuel fabrication technology and experience part I: metal fuels and assembly design

“…In addition, Zr-sheathed fuel slugs exhibited significantly less axial elongation than did standard cast fuel slugs, while producing no significant increases in fission gas pressure or volume [48]. However, residual cracks were observed in the Zr metal periphery of the fuel slugs; thus, the mold does not serve as an adequate barrier to fuel/cladding interdiffusion.…”

Fuels for sodium-cooled fast reactors: US perspective

“…Studies of U-PuZr and cladding interdiffusion found that interdiffusion zones would melt under simulated transient conditions at temperatures as low as 675°C, leading to cladding penetration and breach [33,39]. The beneficial effects of Zr at the fuel/cladding interface were exhibited in various ways (e.g., [40]). The practical effects of these phenomena were manifest in limits derived through conservative application of analytical methods to determine Limiting Conditions of Operation (LCOs) of EBR-II fueled with a U-Pu-Zr driver core [41].…”

Performance of FCCI barrier foils for U–Zr–X metallic fuel

“…Effectiveness of a Zr liner in mitigating pellet cladding interaction (PCI) for boiling water reactor (BWR) fuel is well established [14]. Crawford et al fabricated a U-Pu-Zr fuel rod by injection casting into Zr sheath tubes [12]. When irradiated in the EBR-II up to 6 at.% burnup, the Zr-sheathed fuel showed good performance.…”

“…Ferritic martensitic steels (FMS) such as HT9 and T91 are considered as candidate cladding materials for a SFR fuel due to their excellent irradiation performance [11]. Recently, a thin coating on the inside wall of cladding has been proposed to retard any interaction between the metallic fuel and its cladding [12,13]. Effectiveness of a Zr liner in mitigating pellet cladding interaction (PCI) for boiling water reactor (BWR) fuel is well established [14].…”

“…When irradiated in the EBR-II up to 6 at.% burnup, the Zr-sheathed fuel showed good performance. Tokiwai et al reported that the interdiffusion between U-Zr and HT9 was reduced when a ZrN layer or a V foil were formed on the HT9 cladding [12]. Keiser and Cole compared the out-of-pile diffusion couples tests of Zr or V disks against a 65U-19Pu-9Zr-2.5Mo-2.5Ru-2Nd alloy (compositions in wt%) [15].…”