Overview of ageing and degradation issues in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 338

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Overview of ageing and degradation issues
in light water reactors (LWRs)

K. L. MURTY , North Carolina State University, USA and
K. RAMASWAMY , Bhabha Atomic Research Center, India

DOI : 10.1533/9780857097453.1.3

Abstract : A typical light water reactor (LWR) has components like the
clad, the internals, the reactor pressure vessel (RPV), the heat exchanger
tubes, etc., made from different materials. Some of these components
experience pressure and temperature effects while others experience
an additional contribution from high neutron fl ux. These components
undergo degradation to various extents based on the severity of
service conditions and their inherent material properties. This chapter
presents an overview of the various deformation modes that materials
are known to undergo under reactor operating conditions, and the
known theoretical or empirical relations between the crucial material
and environmental parameters are outlined. Materials degradation
phenomena briefl y described in the chapter include radiation damage,
plastic deformation, fracture and fatigue, following which radiation effects
on these phenomena, as well as corrosion are enumerated. Degradation
mechanisms of concern to specifi c nuclear reactor structures are detailed
in the last section with emphasis on fuel, cladding and internals.

Key words : nuclear reactor, damage, degradation, hydride embrittlement,
life prediction, mechanical property, creep, fatigue, fracture, irradiation
creep, corrosion, irradiation assisted stress corrosion.

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1.1 Introduction

This chapter provides a review of materials ageing and degradation encoun-
tered in light water reactors (LWRs). Ageing of any engineering structure -
through exposure to pressure, temperature and environment - can manifest
as changes in the material properties which may be classifi ed into three
major categories: (1) changes in dimensions or shape of the structure, (2)
changes in material weight due to oxidation, corrosion and erosion and (3)
changes in physical or mechanical properties without any noticeable change
in dimensions. The in-service component(s) may undergo more than one
of the above changes simultaneously, and when these changes affect plant
safety, production effi ciency or economy they are viewed as degradation. In
a thermal energy based power plant (nuclear or fossil fi red), various energy