PULSED POSITRON BEAM IN INVESTIGATION OF REACTOR STEELS

Vladimír Slugeň - Gottfried Kögel - Peter Sperr - Werner Triftshäuser

   The improved pulsed low-energy positron system (PLEPS) was used for positron lifetime spectroscopy in the investigation of irradiated nuclear reactor pressure vessel (RPV) steels microstructure. This system allows to study the microstructural changes in the region from 20 to 600 nm with small and very thin specimens by reducing the disturbing ⁶⁰Co contribution to minimum. Such disturbance was the limiting factor for investigation of high-irradiated RPV specimens in the past. In the frame of the so-called "Extended surveillance specimens program'' started at the 3^rd and 4^th units of the nuclear power plant (NPP) Bohunice (Slovakia) in 1994, well-defined specimens were placed into irradiation channels and taken out after 1, 2 and 3 years in operated VVER-440 reactor, respectively. Samples from RPV base material (15Kh2MFA) and weld material (Sv10KhMFT) were measured before and after irradiation by neutron fluency in the range from 7.8x10²³m^-2 up to 2.3x10²⁴m^-2. Results from PLEPS measurements were correlated with those from other spectroscopic methods (Mössbauer spectroscopies and HV10) and discussed in detail.

Keywords: nuclear safety, defects, positron annihilation, positron beam

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