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I The submitted menucript has been authored by a contractor of the U.S. Government under contract No. W.31-109-ENG-38. Accordingly, the U. ,q. Government retains e ','_' +_ _1. or rlmro<:luce the published form of trois contribution, or allow others to do f.o, for U. S. Government t_Jrposes.

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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.