Corrosion in pressurized water reactors (PWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 3

100 40

Fe
Cr
Ni
O

90

35

80

30

70

25

60

50 20

40

15

30

10

20

5

10

0 0

0 50 100

Position (nm)

150

2.1 EDX profi le on 304 L exposed to water (360°C, pH 325°C = 7.2).

Finally, passivation is the process of building a protective layer of oxide isolating
the surface of the material from the aggressive environment. Some corrosion
inhibitors help the formation of such layers. Figure 2.1 shows energy-dispersive
x-ray (EDX) analysis of the oxide formed on stainless steel exposed to water
at 360°C (−600 mV SHE , pH 325 ° C = 7.2). The passive fi lm is the 50 nm-thick layer
containing a signifi cant level of chromium at the surface of the metal.

￿ ￿ ￿ ￿ ￿ ￿

2.2 Pressurized water reactors and the main

types of corrosion

2.2.1 PWRs

A large variety of structural metals present in primary and secondary
circuits of PWRs suffer corrosion:

￿ Carbon steels are cheap iron-base metals with less than 1% of alloying

element present. These materials exhibit a poor resistance to corrosion
but their forming, machining and welding are superior.

￿ Low-alloy steels are iron-base metals containing a few percent of, for

example, nickel, chromium, molybdenum, vanadium, which are usually