Overview of ageing and degradation issues in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 392

(a)

3.6

11

25.1

5

0.1

0.4

54.8

Crud/Corr Debris Fabricat Gr-R Fret

Handling PCI-SCC Unknown

(b) 24%

32%

9%

4%

31%

Crud/Corr Debris Fabricat PCI-SCC Unknown

1.34 Fuel leaker causes in (a) PWRs and (b) BWRs. 92

around 87% of fuel failures in BWRs while a relatively low proportion
(9%) was noted to be due to PCI/SCC. Many of these issues are dealt in
detail in Part II of this volume.

￿ ￿ ￿ ￿ ￿ ￿

1.4.3 PWR internals

The internals (fl ux thimble tube, lock bars, baffl e bolts and re-entrant cor-
ners) are made from austenitic stainless steels of type SA304, 316 or 347.
The insignifi cantly low swelling behaviour, observed from the limited tests
conducted in environments that are more severe than those of a PWR, is
believed to be associated with irradiation-induced formation of very fi ne
precipitates (such as G phase, carbides and

' phase) in high number density
whose interfaces act as effi cient sinks to irradiation-induced vacancies and
thereby the agglomeration of the vacancies is suppressed. 92

γ