WWER steels

Other reference temperatures using To have been developed for WWER steels. For example, the TACIS IRLA project has defined different values of RTto as follows (Ballesteros and Brumovsky, 2001) ... 

Similar but varying results accrue as a result of other sensitizing elements, such as nickel, manganese, silicon and phosphorus. Moreover, the effects are similar for the WWER steels, with copper and phosphorus being the dominant elements present in the WWER-440 reactors, but with nickel and manganese being the dominant elements present in the WWER-1000 reactors. 

In a manner similar to the effects of irradiation on the CVN impact toughness, the fracture toughness is reduced by irradiation and exhibits a transition temperature shift as well as a reduction in/i and tearing modulus. Examples of these effects are shown in Figs 10.9a (Nanstad et al, 1992) and 10.9b Hiser et al, 1984) for two western RPV steels, while the effects on WWER steels are similar. As with CVN impact toughness, the effects of irradiation on the fracture toughness of RPV steels are dependent on the radiation sensitivity of the material which is primarily determined by the specific chemical composition. 

Within FP-5 project RETROSPEC work will be done to improve the evaluation of the neutron doses induced in reactor structural materials in those cases where no or unreliable data from surveillance specimens are available (for example the older generation of WWER-440 type reactors). The objectives of this project are to develop procedures and guidelines for retrospective dosimetry which are independent of the type of steel and of the time elapsed after removing the material from the reactor. 

B.Timofeev, M. Brumovsky, and U. von Estorff, Certification Report oflSKhlMFA/ 15Cr2MoVA Steel and its Welds for WWER Reactor Pressure Vessels, IRC 57754, Petten, Netherlands EUR 24581 EN, Luxemburg, 2010. 

Steels for WWER-type RPVs are of low-alloyed type, mostly with bainitic microstructure, and thus their radiation damage nature is, in principle, identical with all other RPV steels, with matrix damage, formation of copper-rich precipitates and solute segregation in grain boundaries. Additionally, in materials with a high nickel content, the existence of a late blooming phase is not excluded. 

The beltUne regions of the WWER-440A -213 (i.e. second generation) pressure vessels were also manufactured from 15Kh2MFAA steel, but most of the V-213 pressure vessels have low phosphorus and copper contents and are similar in impurity content to the WWER-1000 pressure vessels with strict requirements on the residual element (copper, phosphorus, arsenic, tin and antimony) content, i.e. their steel and welds are of 15Kh2NMFAA quality. Thus, radiation embrittlement does not seem to be a limiting factor... 

Original trend curves given in the Russian Code have been updated in the last several years, and the current situation can be found either in the last IAEA VERLIFE procedure or in the leading Russian document. The values of Ap, n and a for specified temperatures of irradiation of materials for WWER-440 RPVs from 15Kh2MFA-type steel are given in Table 5.1. The upper boundary for 15Kh2MFA(A) materials and their welding joints... 

Embrittlement of RPVs in WWER-type reactors 111 Table 5.1 Values of irradiation embrittlement of steel 15Kh2MFA... 

Plots of fracture toughness, /(j, results for irradiated (a) western RPV steels (Sokolov and Nanstad, 1999) and (b) WWER-440 steels (Brumovsky, 2001). The data are normalized to To. 

Amayev A D, Kryukov A M and Sokolov M A (1993), Recovery of the transition temperature of irradiated WWER 440 vessel metal by annealing, pp. 369-379 in Radiation Embrittlement of Nuclear Reactor Pressure Vessel Steels An International Review (Fourth Volume), ASTM STP1170, L E Steele, ed., American Society for Testing and Materials, Philadelphia, PA. 

In 2005, Debarberis et al. developed a semi-mechanistic model applicable to the WWER RPV steels. The embrittlement mechanisms, matrix damage, Cu-precipitation and phosphorus segregation were considered, resulting in the following equation ... 

Plate VII (Chapter 10) Plot of fracture toughness data for WWER-440 RPV steels, showing that data from both types of steels are well described by the Master Curve. Note KCJ here is equivalent to Kj, (Brumovsky and Ballesteros, 2002). 

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