2. Material degradation and ageing in BWR service and their mitigation

2.1 Material ageing and degradation

During prolonged operation, the (synergistic) effects of the thermo-mechanical and thermo-hydraulic loading, increased temperatures, reactor coolant and the irradiation field can progressively result in:

• changes of material properties (strength, toughness, corrosion resistance, etc.)

• initiation and propagation of cracks (SCC, fatigue)

• changes of component dimension/geometry (FAC, plastic deformations, distortions, etc.)

These slowly progressing, operation-induced changes or degradation/damage in the materials are called physical ageing. There are around 50 different potential degradation mechanism...