PSI - Issue 22

Maksym Zarazovskii et al. / Procedia Structural Integrity 22 (2019) 305–312 Maksym Zarazovskii and Yaroslav Dubyk / Structural Integrity Procedia 00 (2019) 000 – 000

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The second example is related to the initial CBT and its effect on the irradiation embrittlement. Fig. 5 shows the examples of radiation embrittlement definition of base metal of Unit #1 RPV of Zaporizhzhya NPP based on the CTB shift ideology. We can see, that depending of initial CTB we can obtain as slight embrittlement, as the absence of embrittlement.

Fig. 4. The CTB curves of weld #3 of Unit 1 RPV of South-Ukrainian NPP

Fig. 5. Example of radiation embrittlement definition of base metal of Unit #1 RPV of Zaporizhzhya NPP based on the CTB shift ideology.

It should be noted, that initial CTB is random value, which inherent data scatter. Related to the base metal of Unit #1 RPV of Zaporizhzhya NPP, itself we can do estimation, based on the principle of conservatism. But, what if we have the only one point of initial CTB, for instance the lowest (the realization of the SS program differs from one reactor to another, and in half cases we have the only one initial CTB)? Then, according to the actual normative, in some cases we must to make illogical conclusions. Therefore, the usage of actual CBT data and its scatter (obtained directly from Charpy V-notched impact tests) instead of the CTB shift ideology should be the progressive way of adequate CTB curve prediction. Also, it is important to note, that in modern methodologies of RPV brittle fracture assessment in the WWER countries disregard the chemical factor for embrittlement estimation. The one way of its consideration, is developed by Orynyak et al. (2015). The paper presents CTB dependence on the neutron fluence and chemical composition of WWER-1000 RPV beltline welds as well as a new methodology of CTB curve prediction for WWER-1000 RPV welds. Obtained chemical factor contradicts with VERLIFE’s (2008) ones for probabilistic RPV brittle fracture assessment. The dependence can be used as for deterministic RPV brittle strength assessment as well as for probabilistic ones. Proposed methodology is expected to be the basis in the modern Ukrainian normative of RPV integrity assessment since it reduces the unreasonably high conservatism inherent to the RPV project, to a more reasonable level and consider a chemical factor.