ISSN: 1546-962X
Published Online: 16 September 2008
Page Count: 16

Influence of Structure Changes in E110 Alloy Claddings on Ductility Loss Under LOCA Conditions

Nikulin, S. A.
Professor, Head of Department, Moscow State Institute of Steel and Alloys, MSSP Department, Moscow,

Rozhnov, A. B.
Senior Lecturer, Moscow State Institute of Steel and Alloys, MSSP Department, Moscow,

Belov, V. A.
Post Graduate Student, Moscow State Institute of Steel and Alloys, MSSP Department, Moscow,

Lyaschenko, N. V.
Post Graduate Student, Moscow State Institute of Steel and Alloys, MSSP Department, Moscow,

Nikulina, A. V.
Chief Expert, FSUE A. A. Bochvar VNIINM, Moscow,

Mal‘gin, A. G.
Engineer and Post Graduate Student, FSUE A. A. Bochvar VNIINM, Moscow,

(Received 15 March 2007; accepted 3 April 2008)

Abstract

Microstructural changes are analyzed in specimens of E110 cladding tubes that have varying total impurity contents and differing residual ductility after interaction with steam at 1100 and 1200°C to 10–18 % ECR. It is shown that characteristics of the microstructure and the fracture behavior of tube specimens substantially depend on attendant impurities (C, Si, Ni, P, Cl, etc.). The total content of impurities available in the E110 alloy tubes varied from 35 to 140 ppm. With an increase in steam temperature from 1100 to 1200°C the influence of impurities on ductility of the tubes becomes weaker. The results of X-ray spectral examinations of niobium and oxygen distributions and microhardness measurements within the cladding wall after high temperature oxidation are presented. Methods of optical and electron microscopy were used to quantitatively analyze the interrelation between microstructural changes and fractures characteristics as a result of interaction with the high temperature steam environment. This work has suggested the likely reason for the losses of ductility in the studied specimens is the different contents of impurities that govern the types of microstructures formed as a result of the β →α transformation in the prior-β region of the specimens. The primary microstructural characteristics that govern the residual ductility of the E110 specimens is the morphology of the α phase platelets in the prior-β region (parallel plate or basket weave), and the quantity and brittleness of a second “dark” phase precipitate in the prior-β region.

Keywords:
LOCA, zirconium alloys, residual ductility, impurities, microstructure, fractography

Paper ID: JAI101148
DOI: 10.1520/JAI101148
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