Surveillance welds

Depending on the amount of weld material in a given heat, many different RPV and surveillance welds could have been made with each unique combination. Similarly, different flux lots could also have been qualified with the same heat of weld wire. Once a welding procedure was qualified, this procedure was typically used for many welds over a time period that could span several years. 

A/ 7iMDTof Japanese PWR surveillance weld metals as a function of neutron fluence. 

The surveillance welds were not actual RPV welds but had been made by reproducing the RPV manufacturing process with appropriate weld parameters and consumables. 

Figure 6 shows the histogram of localized AE events vs axial position for the same time period as in fig.5. The location of the AE source corresponds, within source location errors (< 10-15 cm), to one of the welds under surveillance. The weld was known by ultrasonic examination to be affected by internal discontinuities. However, the position of the source could also correspond to one of the hangers. The steps observed in EA event accumulation have taken place during steady load operation, which normally corresponds to very low background noise conditions. This type of event, however, has not been observed afterwards. 

Calculation of the so-called fluence factor of the copper impact into the transition temperature shift confirms that for the value fluence about 0.0002 dpa saturation of this factor is observed already. The attempt to separate out the embitterment data into the two components of CEC and AfDg was carried out . It was found that the copper component remains unchanged already due irradiation 0.0005 dpa at 190-200°C of weld surveillance material. Similar analysis for PWR submerged-arc weld material following accelerated irradiation at temperatures in the range 255-315°C shows that copper contribution remains unchanged after irradiation with dose of 0.01 dpa. 

Again, hot work is that type of work that involves welding, grinding, cutting, and other flame- or potential spark-producing activity that might be performed in the vicinity of processes covered by the process safety management rule. The hot work permits provide for fire safety in conjunction with that type of work and typically include written authorizations and procedures for special controls and surveillance requirements. Most important is the coordination of maintenance and operations. 

To provide flexibility in the surveillance program, archive materials are set aside to permit testing and analysis in the future. Test stock (comprising base metal, weld metal and HAZ material) sufficient to fill two capsules is to be retained with full documentation and identification. 

Table 4.5 gives an example of the content of capsules of 900 MWe reactors. Charpy V-notch tests are used to monitor all the materials. Additional tensile and fracture toughness tests are carried out for base and weld metals. Most reactors have four surveillance capsules to cover their design lifetime (40 years), except the first series of six 900MWe reactors known as CPO which have eight capsules. Generally, capsules are planned to be removed so that irradiation at quarter, half, three-quarters and completion of the component design end-of-life fluence can be achieved (Brillaud and Hedin, 1992 Chas et al, 2004). Table 4.6 shows the lead factors, defined by... 

Relationship between nickel and copper contents of base metals and welds monitored in the French surveillance program. Circled symbols refer to Chooz-A materials. 

Transition temperature shifts versus fluence for base metals, weld metals, heat-affected zones and correlation monitor material from French surveillance program. 

Taking into account the fourth withdrawn capsules of the standardized CPY reactors (27 capsules exposed in reactor between 14 and 17 years with a lead factor close to 3 for standard fuel management), the mean base metal shift is close to 60 °C for a mean fluence of 7 x lO n/cm. The corresponding weld metal shift is close to 54°C for a mean fluence of 5.5 x 10 n/cm. The published dataset (Brillaud and Hedin, 1992), updated according to surveillance reports in force today, and augmented with Tm shifts is given in Table 4.7. 

Table 4.13 Japanese PWR surveillance database (weld metal)...

The neutron flux level for the PWR surveillance program is approximately 10 n/cm s ( > 1 MeV). The highest fluence of the PWR surveillance data is about 6 x 10 n/cm (E > IMeV) as of 2012. The transition temperature shifts, ARTndtS, of all the PWR surveillance data are plotted in Fig. 4.12 for base metals and Fig. 4.13 for weld metals as a function of neutron fluence. In general, ARTndt increases with fluence, but the values of the shift are not very high. The highest ARTndt values for base metal and weld metal are 88 °C and 131 C, respectively. The transition temperature shift depends mainly on the copper content of steel, and it increases with the copper content. 

Transition temperature shifts versus fluence for weld metals from German FWR surveillance results (Langer ef a ., 2000). 

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