Corrosion in pressurized water reactors (PWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 1

2
Corrosion in pressurized water
reactors (PWRs)

T. COUVANT , EDF R&D, France

DOI : 10.1533/9780857097453.1.70

Abstract : Corrosion is one of the major obstacles to extending the
lifetime of nuclear power plants within agreed safety requirements. A
large variety of the structural metals present in primary and secondary
circuits of pressurized water reactors (PWRs) suffer corrosion. Uniform
corrosion, fl ow-accelerated corrosion (FAC), pitting, stress corrosion
cracking (SCC), environmentally assisted fatigue and hydrogen
embrittlement can all affect the major components of PWRs, despite
stringent selection of materials for component manufacture. Remedies
can vary: adjusting water chemistry, reducing superfi cial strains and
stresses, replacing materials or changing microstructures. Experience
in the fi eld has demonstrated that increasing chromium content is an
effi cient strategy: to date nickel alloys containing 30% chromium exhibit
very good resistance to corrosion such as SCC. It can be shown that
tendency to corrosion can largely depend on manufacturing conditions.

Key words : corrosion, austenitic alloys, pressurized water reactors,
primary water, cracking.

2.1 Introduction
We begin the chapter with an outline of the history and fundamental prin-
ciples of corrosion.

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2.1.1 History

Corrosion and its effects have been observed since the fi rst steps in metal-
lurgy. Corrosion damage increased with the use of iron over the centuries. In
1830, de la Rive (1801-1873) showed that bimetallic junctions suffered fast
corrosion due to impurities present in zinc. Later, Faraday (1791-1867) cor-
related the current fl ow with the associated rate of corrosion. In the 1930s,
Wagner (1901-1977) showed that the uniform dissolution of metals did not
require separate anodic and cathodic sites but that metal dissolution and
the accompanying cathodic reaction can occur randomly with respect to
space and time over the surface. In the 1950s, Pourbaix (1904-1998) edited a
series of major diagrams giving the domain of stability of many elements as
a function of potential and pH.