Irradiation ductile fracture toughness

Sulfur dioxide was the major volatile product and was used as a probe to correlate the radiation resistance with polymer structure. The use of biphenol in the polymer reduced G(SO ) by 60% compared with bisphenol A based systems (Bis-A PSF). Surprisingly, the isopro-pylidene group was shown to be remarkably radiation resistant. The ultimate tensile strain decreased with dose for all polysulfones investigated and the rate of decrease correlated well with the order of radiation resistance determined from volatile product measurements. The fracture toughness (K ) of Bis-A PSF also decreased with irradiation dose, but the biphenol based system maintained its original ductility. 

Key words fracture toughness, J-integral, master curve, irradiation, crack-arrest, embrittlement, Charpy impact, nil-ductility transition (NDT) temperature, pressurized water reactor (PWR). 

Mechanical properties of the in-core components change as a result of the fast neutron flux damage. The strength increases and ductility and fracture toughness decrease to shelf levels that are acceptable for service. Recent developments in pressure tube technology have made the pressure tubes more resistant to decreases in fracture toughness caused by irradiation. 

Wrought austenitic stainless steels do not exhibit the sharp ductile to brittle transition behavior characteristic of low alloy and carbon steels. Rather, toughness losses due to irradiation tend to accumulate with increasing fluence and saturate at levels >1x10 n/m. Until recently, there was little information available to quantify the effects of radiation embrittlement on RPVIs. New information [5.2] describes the results of a fracture toughness study performed on irradiated Type 304 stainless steel reactor internal material taken from... 

Neutron irradiation of steels used in the construction of nuclear reactor pressure vessels can lead to the embrittlement of these materials - an increase in the ductile-to-brittle transmission temperature and a decrease in the fracture energy - which can limit the NPP. Embrittlement is manifested as a reduction in the fracture toughness and a shift in the ductile-to-brittle transition temperature (DBTT) to higher values, as shown schematically in Figure 4.17. The upper limits on neutron fluence for RPV materials are listed in Table 4.12 [52]. 

Figure 10.8a shows the effect of irradiation on the tensile fracture stress with the corresponding effect on the Charpy impact toughness in Fig. 10.8b as a shift of the ductile-brittle transition to higher temperatures and... 

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