PSI - Issue 68

Aleks Vainionpää et al. / Procedia Structural Integrity 68 (2025) 279–284 A. Vainionpää et al. / Structural Integrity Procedia 00 (2025) 000–000

281

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Table 2. Nominal parameters for the HTA and simulated PWR environments. Unit Air

PWR

Temperature T

°C

300 ± 3

300 ± 3

Relative humidity

%

< 30

-

Pressure P

bar

atmospheric

150 (min)

[Li] as LiOH [B] as B(OH)3

ppm ppm ppb

- - - - - -

2 ± 0.2

1000 ± 100

Dissolved Oxygen O2 Dissolved Hydrogen H2

< 5

cc∙kg-1

25 ± 5

pH300°C

6.95

Conductivity

µS cm-1

17–20

3. Results The primary crack initiation sites/paths, visible under/overload marks, and secondary cracks were identified from LOM/SEM fractography images, as shown in Figure 1. In this paper, specimens subjected to loading with and without VA loads are evaluated. For specimens without VA loads, the striation spacing was evaluated from the base load striations. For specimens subjected to VA loads, visible periodic under/overloads can be "mapped" on the fracture surface, which allows backwards tracking and reconstruction of crack progression history from the last under/overload down to the initiation site. Such "VA-maps" provide a consistent and precise method for evaluating the striation spacing and cycles-to-depth in VA-loaded specimens, as demonstrated in Figure 1. Crack depth as a function of cycle number, as well as the striation spacing between a pair of under/overloads can be accurately measured since the number of base load cycles per block (200) is known. Furthermore, the evaluation based on "VA-maps" can be faster than measuring and averaging base load striations from multiple locations. In addition to this, the base load striations can become faint or invisible due to oxides/scales or local microstructure, which may result in lack of reliable data points in some regions. The VA-marks are not as prone to become invisible due to oxidation.

Fig. 1. Example of a specimen tested with PUL-type VA-loading in PWR water. The periodic underloads are visible throughout the fracture surface and can be used to reconstruct the crack progression history.