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Extra resources for Ageing of Nucl. Powerplant Compnts. - BWR Pressure Vessel Internals (IAEA TECDOC-1471)

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Fatigue behavior is related to a variety of parameters, such as stress range, mean stress, cycling frequency, surface roughness and environmental conditions. Cracks initiate at stress concentrations such as geometric notches and surface defects. Fatigue initiation curves indicate how many stress cycles it takes to initiate fatigue cracks in components. These curves are materials related and indicate the allowable number of stress cycles for applied cyclic stress amplitudes. Design curves for RPV materials are given in ASME Section III, Appendix I or respective national standards such as KTA 3204 or METI notification 501.

Stress corrosion cracking Stress corrosion cracking (SCC) is the term given to crack initiation and sub-critical crack growth of susceptible alloys under the influence of tensile stress and a “corrosive” environment. SCC is a complex phenomenon driven by the synergistic interaction of mechanical, electrochemical and metallurgical factors. BWR internals are potentially susceptible to two predominant forms of SCC. These are: (1) intergranular stress corrosion cracking (IGSCC) and (2) irradiation assisted stress corrosion cracking (IASCC).

44 TABLE 4-2a EPRI WATER CHEMISTRY GUIDELINES REACTOR WATER –NWC- POWER OPERATION (>10% Power) a Note: This table applies to site specific target components exposed to NWC environments or not protected to –230 mV(SHE) by HWC. 0 Chloride (ppb) Daily b >5 >20 >100 Sulfate (ppb) Daily b >5 >20 >100 Zinc (ppb) c --- Diagnostic Parameter Frequency of Measurement Oxygen (ppb) Continuously Silica (ppb) --- Co, Zn (Zinc plants only) d 60 65 Iron (ppb) Weekly Sample Monthly Comments --b --(e) Notes: (a) If HWC is not incorporated into the station chemistry program, an engineering evaluation should be performed to support the decision using an appropriate assessment methodology.

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Ageing of Nucl. Powerplant Compnts. - BWR Pressure Vessel Internals (IAEA TECDOC-1471)


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