RPV annealing in WWER reactors

Irradiation embrittlement in RPVs mainly results in two consequences. First, it narrows the pressure-temperature operation window for normal operating conditions. Second, it limits RPV lifetime as the transition temperature of RPV materials cannot be higher than that determined from the pressurized thermal shock (PTS) calculations. Several mitigation measures can be applied to decrease radiation embrittlement of RPV beltline materials  

The principal scheme of the whole process of RPV material embrittlement before and after annealing is shown in Fig. 5.13. In this diagram, C means conservative shift , where the re-embrittlement rate is equal to the initial one, L means lateral (or horizontal) shift , where the re-embrittlement rate has shifted horizontally to the right from zero fluence, and V means vertical shift when the re-embrittlement rate is equal to the initial rate for lluences larger than those before annealing. Most of the experimental data lie between lateral and vertical shifts thus the lateral shift could be taken as a conservative one. In this diagram, two important parameters are included  

The residual value, ATT esiduai, in practice represents the efficiency of the annealing process. This value depends on annealing temperature and annealing time (holding at annealing temperature). Most experimental results have shown that an annealing temperature between 430 and 475 °C is sufficient for substantially efficient recovery of initial properties. Recovery time for efficient recovery was determined as a minimum of 100 hours. 

Irradiation Embrittlement of Reactor Pressure Vessels (RPVs) 

14 The effect of isothermal annealing on the recovery of mechanical properties in 15Kh2MFA steel irradiated to a fluence at 130°C. 

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