Nuclear Science User Facilities 108 Destructive PIE Major changes were implemented in the procedure to prepare metal- lography samples for these pins as compared to previous PIE investiga- tions carried out on FO-2 pins. It is known that with increasing burnup, part of the fission products, particu- larly cesium and molybdenum, leave the fuel matrix and accumulate in the fuel-to-cladding gap, forming the so-called joint oxyde gaine (JOG) . Historical electron probe micro- analyzer (EPMA) data  and ther- modynamic calculations  suggest Cs2MoO4 as one of the major compo- nents of the JOG.The compound is highly hygroscopic and tends to dissolve rapidly when in contact with water, which was the main cutting fluid used in the past.The new sample preparation procedure uses non-water-based solutions and cleaning with ethanol—thus allowing Figure 5. High-magnification image (200×) showing the formation of JOG and metallic rivers around one of the fuel cracks. Figure 4. Low magnification cross section images (50x) from pin K06 at different axial positions. (a) Relative axial position 0.5 (peak power node) and (b) 0.05.