Nuclear fuel cladding system

The invention provides an elongated slender fuel element of cylindrical form having a locally flexible metallic sheath, a plurality of close-fitting nuclear fuel pellets in end-to-end stacked array therein, having longitudinal expansion relief provision in the ends of at least some pellets to substantially preclude differential axial expansion between pellet and sheath in operation, and a low-shear lining layer composed of siloxane lacquer or graphite interposed between the pellets and the sheath at the peripheral adjoining surfaces thereof to facilitate peripheral distribution of stresses in the sheath to reduce the likelihood of rupture failures extending longitudinally of the sheath due to a concentration of peripheral sheath expansion stresses