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Title:Influence of zirconium hydride on the biaxial creep behavior of Zircaloy-4 cladding for interim dry storage of spent nuclear fuel
Author(s):Lan, Kuan-Che
Director of Research:Stubbins, James F
Doctoral Committee Chair(s):Stubbins, James F
Doctoral Committee Member(s):Heuser, Brent J; Allain, Jean Paul; Bellon, Pascal
Department / Program:Nuclear, Plasma, & Rad Engr
Discipline:Nuclear, Plasma, Radiolgc Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):zirconium alloys
Zircaloy-4
biaxial creep
hydride
dry storage
texture
EBSD
synchrotron
Abstract:Zircaloy-4 is widely used in light water reactors (LWRs) for fuel cladding applications because of its low absorption cross-section of the thermal neutron. The integrity is especially crucial for the containment of fission products in used nuclear fuel (UNF) during a long term storage. The creep rupture of high burnup UNF (>45 GWD/MTU) cladding is a concerning failure mechanism during long-term dry storage. A high amount of zirconium hydride deposited in the cladding matrix, which is accompanied by radiation damage accumulated at the high burnup limit, would degrade the mechanical performance of the cladding, particularly if radial hydrides occur. Hydrides normally occur in the circumferential orientation which is less likely to lead to cladding fraction than hydrides oriented radially. To better understand the influence of zirconium hydride on the biaxial thermal creep of Zircaloy-4 cladding, the pressurized tube technique is employed in this study to test the durability of the material. Test are performed on as-received Zircaloy-4 tubular specimens as well as as-hydrided ones with 300 wppm or 750 wppm hydrogen. The biaxial creep experiments are conducted at temperatures from 300 ◦C to 500 ◦C and at effective stresses from 40 MPa to 65 MPa. The hydriding process prior to creep tests induces the formation of fcc δ-hydride platelets along the circumferential direction of the tube. This alignment and phase structure of hydride show no significant change after biaxial creep tests. However, the relation between hydrogen concentration and creep strain rate at high temperature (500 ◦C) is opposite to that at low temperatures (< 500 ◦C). The synchrotron wide-angle X-ray scattering (WAXS) technique, as well as electron backscatter diffraction (EBSD) analysis, are applied to the sample crept at low temperatures for the study of the crystallographic orientation relationship. Most hydride grain orientation follows α-Zr(0002) || δ-hydride(111) relationship. This relationship is stable even after creep deformation. Through the post-creep, room temperature tensile tests on samples crept at low temperature, exhibit low ductility in the specimen with the high hydrogen concentration. The total elongation of Zircaloy-4 with 750 wppm H is about half of that of the as-received Zircaloy-4. These characterizations and observations demonstrate the influence of zirconium hydride on both the biaxial creep behavior and mechanical performance of Zircaloy-4 cladding. The goal of this study is to develop a better understanding of materials performance to support the design basis of interim and long-term dry storage facilities for up to 300 years.
Issue Date:2017-12-06
Type:Thesis
URI:http://hdl.handle.net/2142/99243
Rights Information:Copyright 2017 Kuan-Che Lan
Date Available in IDEALS:2018-03-13
Date Deposited:2017-12


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