The Swiss Research Program on Irradiation Embrittlement and Annealing of Reactor Pressure Vessel Steels

Abstract

The present research program on irradiation embrittlement and annealing of reactor pressure vessel (RPV) steels in Switzerland is carried out at the Paul Scherrer Institute for Reactor Research. The particular program structure and its relation to the concept for an improved surveillance program is described. Based on past experience with surveillance programs, especially for older plants, the main goal of the research program is determined by an effort to overcome identified shortcomings.Therefore the following topics are discussed: 1. Obtaining additional data to supplement those from specific surveillance capsules. 2. Understanding the mechanisms of irradiation embrittlement by microstructural investigations of the materials. 3. Investigations of the annealing-recovery behavior of irradiated RPV steels. 4. Validation efforts concerned with the transferability of test reactor and surveillance program results to the real RPV. Within the framework of bilateral research agreements, participation in research programs coordinated by the International Atomic Energy Agency (IAEA), and collaborative research with other Swiss and foreign institutions, a review of past and future activities is presented; the technical facilities (irradiations, mechanical testing, physical methods) and the advanced and new tools used in the investigations, especially those for the microstructural studies, are outlined and put into perspective. Finally, first results obtained in the research program are summarized.

Neutron induced damage in reactor pressure vessel steel: An X-ray absorption fine structure study

“…The neutron irradiation was performed in the 10 MW SAPHIR reactor [at a neutron flux of $ 4 Â 10 12 cm À2 (fast component >1 MeV)] in Switzerland according to the reactor parameters described in Ref. [18], and at various fluences in the range 0:85-5:0 Â 10 19 cm À2 . The irradiation temperature was controlled at 560 AE 5 K. Thermal annealing (at 735 K for a duration of 168 h) of irradiated samples was conducted in a hot cell under a protective gas atmosphere.…”

“…The displacement-per-atom (dpa) parameter was calculated in order to characterize the radiation damage level. For the calculations, the neutron flux spectrum [18] has been used as input to the SPECTER computer code [19]. A simplified calculation gave the dpa doses ranging from 1:2 Â 10 À2 to 7:1 Â 10 À2 dpa for 0.85 to 5:0 Â 10 19 cm À2 exposed specimens, respectively, if the threshold energy for Fe displacement is assumed to be 24 eV.…”

The effects of flux on the radiation-induced embrittlement of reactor pressure vessel steels: review of current understanding and application to high fluences

“…This MD contribution added increasingly to hardening at fluxes above 4 × 10 12 n.cm −2 s −1 . Data (Mader, 1995) from steels with <~0.01 wt% Cu confirmed that the appropriate trend occurred when only matrix damage was present, as illustrated in Figure 1.…”

“…In the 1990s Odette and co-workers exposed A533B-type steels of multiple compositions at high fluxes 5 × 10 11 -6 × 10 13 n.cm −2 s −1 , in the University of Virginia and PLUTO MTRs (the UV-P campaign) (Odette et al, 1993;Mader, 1995). They found that hardening at a given fluence in 0.4 wt% Cu steels decreased with increasing flux while that in 0.11-0.16 wt% Cu steels increased.…”

Effect of lead factors on the embrittlement of RPV SA-508 cl 3 steel

“…CRP damage is one of the two contributions to embrittlement better known experimentally. Both transmission electron microscopy (TEM) and techniques such as positron annihilation spectroscopy (PAS), Mössbauer spectroscopy (MS), thermoelectric power (TEP), anomalous small-angle X-ray scattering (ASAXS) [23] and small-angle neutron scattering (SANS) [22] have allowed the experimental characterization of the size of the precipitates, the relative number of these nanostructures, their composition and their volumetric fraction [19][20][21].…”