Creep deformation of materials in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 12

3
Creep deformation of materials in
light water reactors (LWRs)

K. L. MURTY , North Carolina State University, USA,
S. GOLLAPUDI , Massachusetts Institute of Technology, USA,
K. RAMASWAMY , Bhabha Atomic Research Center, India,
M. D. MATHEW , Indira Gandhi Center for Atomic Research,
India and I. CHARIT , University of Idaho, USA

DOI : 10.1533/9780857097453.1.81

Abstract : The time-dependent deformation of materials or creep
governs the useful life of many engineering structures. It assumes
even higher signifi cance in the case of structures constituting a nuclear
reactor, wherein materials bombarded with neutrons develop defects
that assist faster diffusion leading to greater plastic deformation. As a
result, an understanding of the creep deformation process and factors
controlling it is necessary for gauging the usefulness of materials in a
nuclear reactor as well as for predicting life-times of various structures.
Thus in this work we discuss the various mechanisms of creep, the
rate controlling factors, deformation mechanism maps and useful life
prediction methodologies. We also identify a few cases where direct
application of simple creep correlations might not be feasible. Finally, we
discuss the various factors that control the creep behavior of materials in
light water reactors.

Key words : creep, diffusion creep, dislocation creep, deformation
mechanism maps, modeling, zirconium alloys, stainless steels, irradiation
creep.

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3.1 Introduction

Creep is time-dependent plastic strain under a constant load/stress at a
given temperature and often becomes the life limiting criterion for many
structures that experience loads and temperatures, and becomes signifi -
cant for materials in light water reactors (LWRs) due to imposed radiation
effects. A thorough understanding of the plastic deformation behavior of
materials is essential for the sound design of engineering structures. Fail-safe
designs are based on the ability to predict the response of a structure to
applied loads and ensuing plastic deformation. While brittle materials such
as ceramics fail after relatively low plastic strains, a signifi cant number of