Nanoscale Precipitates in VVER-440-type Reactor Pressure Vessel Steels after Irradiation and Annealing


Nanoscale Precipitates in VVER-440-type Reactor Pressure Vessel Steels after Irradiation and Annealing

Böhmert, J.; Große, M.; Ulbricht, A.

The microstructural evolution of reactor pressure vessel (RPV) steel effected by neutron irradiation is not yet sufficiently understood. The issue, however, is highly relevant for a safe operation of nuclear power plants (NPP).
Investigations have been performed by the methods of analytical high-resolution transmission electron microscopy (AHRTEM), the small angle neutron scattering (SANS) and the anomalous small angle X-ray scattering (ASAXS). The materials selected represent two different state-of-the-art products of VVER-type RPV steels.
One material is typical for the first VVER-440/230 generation and has a quite high content of impurities. The second material consists of surveillance specimens manu factured by Skoda Pilsen for the VVER 440/213 NPP in Paks (Hungary). The materials were irradiated to fluences of 7 to 14x1023 n/m2 (E > 1 MeV) within a high flux channel of the VVER prototype VVER-2 in Rheinsberg (Germany), or in the surveillance position of the Paks NPP, respectively. Whereas the detection of irradiation-induced precipitates by AHRTEM was not successful in every case, SANS showed an increase in the scattering intensity after irradiation, which could be interpreted as caused by a bimodal size distribution of irradiation-induced precipitates. A high first peak of the distribution appears at a radius of the precipitates of 1 to 2 nm. This peak disappears after annealing and is especially high but also thermally unstable for charges with high copper content. ASAXS measu rements prove that these precipitates are vanadium rich. There is a clear correlation between the integral of the sieze distribution within the range of the first peak of the distribution curve and the hardness. The correlation is independent of the treatment or the fluence. This shows the fine-dispersed nano-scale precipitates are the reason of the irradiation hardening.

  • Lecture (Conference)
    Third International Ural Seminar, Radiation Damages Physics of Metals and Alloys, Abstracts, 21-27 February 1999, Snezhinsk, Russia, p. 32
  • Contribution to proceedings
    Third International Ural Seminar, Radiation Damages Physics of Metals and Alloys, Abstracts, 21-27 February 1999, Snezhinsk, Russia, p. 32

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Publ.-Id: 2574