Fine structure behaviour of VVER-1000 RPV materials under irradiation

Metals, 2022

The existing knowledge about the effect of neutron irradiation on the mechanical properties of reactor pressure vessel steels under reactor service conditions relies to a large extent on accelerated irradiations realized by exposing steel samples to a higher neutron flux. A deep understanding of flux effects is, therefore, vital for gaining service-relevant insight into the mechanical property degradation. The existing studies on flux effects often suffer from incomplete descriptions of the irradiation-induced microstructure. Our study aims to give a detailed picture of irradiation-induced nanofeatures by applying complementary methods using atom probe tomography, positron annihilation, small-angle neutron scattering and transmission electron microscopy. The characteristics of the irradiation-induced nanofeatures and the dominant factors responsible for the observed increase of Vickers hardness are identified. Microstructural changes due to high flux conditions are smaller nm-sized ...

2014

In this paper the influence of fast neutron flux on the structural features and properties of VVER-1000 reactor pressure vessel steels was studied. It is shown that for high Ni steels the flux effect is due to hardening and non-hardening mechanisms of radiation embrittlement.

Atomic Energy, 2004

In work on minisamples of the fifth complex of the No. 3 unit of the Kola nuclear power plant it is shown that for neutron fluence 4•10 23 m-2 (operation for approximately 10 yr), neutron flux density 3•10 15 sec-1 •m-2 and copper content 0.03% and 0.09% in the metal the shifts of the cold-brittleness temperature are 50 and 120°C, respectively. Under the same irradiation conditions but with neutron flux density 3•10 16 sec-1 •m-2 , this shift for standard samples is 50°C. These results attest to the state of the vessel material at a given moment in time.

Nuclear Engineering and Design, 1995

The dependence of the mechanical properties on the depth position in the unirradiated state and after irradiation up to neutron fluences of approximately 5 x 1018 and 70 x 1018 cm -2 (E> 0.5 MeV) is tested on a forging made out of VVER 440 reactor pressure vessel (RPV) steel 15CrMoV. The near-surface position shows a higher strength and a lower transition temperature than the positions greater than 1/4 wall thickness. Irradiation does not change these differences in a significant manner. The testing of specimens from the 1/4 depth position within the surveillance programme, as normally laid down in the legal rules relating to nuclear power plants, results in a conservative safety assessment against brittle failure up to the EOL fluence. On taking into account fluence attenuation, the flux effect, etc., the toughness gradually increases from the inside to the outside of the wall after longer RPV operating times. 0029-5493/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSDI 0029-5493(95)01073-4 132 J. B6hmert et al. / Nuclear Engineering and Design 159 (1995)

Scripta Metallurgica, 1984

MRS Proceedings, 2000

ABSTRACTAs part of a broad effort to understand the mechanisms of irradiation embrittlement in reactor pressure vessels steels, irradiation hardening and microstructural evolution in simple model Fe-0.9Cu-1.0Mn, Fe-0.9Cu and Fe alloys irradiated with 3.2 MeV protons at 300°C are compared to the corresponding changes in hardening produced by neutron irradiation over a similar dose range of 0.0004 to 0.015 dpa. In the case of the proton irradiated samples, Vickers hardness was measured at a 25 g load and the microstructures were characterized using small angle x-ray scattering (SAXS). In spite of the much higher dpa rate for protons (3 × 10−7 dpa/s compared to neutron rates of about 10−9 to 10−10 dpa/s) as well as very different primary recoil spectra, the observed hardening-dose response is very similar in both cases. The large increase in hardness in the alloys with 0.9% copper, and the SAXS data are consistent with precipitation of coherent copper-rich features accelerated by irrad...

Journal of Nuclear Materials, 1995

The methodologies published earlier for predicting the upper shelf energy (USE) of full size Charpy specimens based on subsize test data appear to work satisfactorily for either highly ductile materials (USE > 200 J) or relatively brittle materials (USE ~ 100 J). A methodology is proposed here that works well for pressure vessel weld materials in both unirradiated and irradiated conditions having USE in the intermediate region (100 J < USE < 200 J). The methodology uses partitioning of the USE into two components, USE 0 and AUSE (= USE -USEp). USEp is the absorbed energy for a specimen fatigue-precracked to half the width. The predicted value of the USE of full-size specimens is a sum of two terms. The first term is equal to the product of the normalized AUSE of the subsize specimen and the full-size normalization factor for AUSE. The second term is equal to the product of the normalized USEp of the subsize specimen and the fracture volume of the full-size precracked specimen. The predicted values were within about 10% of the measured values for both unirradiated and irradiated materials. 0022-3115/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0022-3 115(95)00050-X

Journal of Nuclear Materials, 2000

The objective of this work is to examine the susceptibility to hardening and embrittlement of Fe7.5/11CrWTaV reduced-activation (RA) and conventional 9/12Cr±Mo martensitic steels as a function of¯uence up to 10 dpa and irradiation temperature in the range of 250±450°C. For this purpose, materials were irradiated in the Osiris Reactor (Saclay) at 325°C for various doses ranging from 0.8 dpa to a maximum dose of 8±9 dpa. Available data concern the evolution of tensile properties for doses from 0.8 to 3.4 dpa. On the other hand, RA-steels were irradiated as Charpy V and tensile specimens in the high¯ux reactor (HFR) at Petten at temperatures ranging from 250°C to 450°C with a dose of about 2.4 dpa. Ó

IOP Conference Series: Materials Science and Engineering, 2016

Influence of neutron irradiation on RPV steel degradation are examined with reference to the possible reasons of the substantial experimental data scatter and furthermorenonstandard (non-monotonous) and oscillatory embrittlement behavior. In our glance this phenomenon may be explained by presence of the wavelike component in the embrittlement kinetics. We suppose that the main factor affecting steel anomalous embrittlement is fast neutron intensity (dose rate or flux), flux effect manifestation depends on state-of-the-art fluence level. At low fluencies radiation degradation has to exceed normative value, then approaches to normative meaning and finally became sub normative. Data on radiation damage change including through the ex-service RPVs taking into account chemical factor, fast neutron fluence and neutron flux were obtained and analyzed. In our opinion controversy in the estimation on neutron flux on radiation degradation impact may be explained by presence of the wavelike component in the embrittlement kinetics. Therefore flux effect manifestation depends on fluence level. At low fluencies radiation degradation has to exceed normative value, then approaches to normative meaning and finally became sub normative. Moreover as a hypothesis we suppose that at some stages of irradiation damaged metal have to be partially restored by irradiation i.e. neutron bombardment. Nascent during irradiation structure undergo occurring once or periodically transformation in a direction both degradation and recovery of the initial properties. According to our hypothesis at some stage(s) of metal structure degradation neutron bombardment became recovering factor. As a result oscillation arise that in tern lead to enhanced data scatter.

Journal of Nuclear Materials, 1999

In order to clarify the mechanism of the large increment of DBTT due to low temperature neutron irradiation, the mechanical properties and the microstructural evolution were investigated in vanadium binary alloys irradiated in JMTR. From a series of microhardness tests conducted on these alloys after irradiation at 90±200°C, the hardness increased with increasing irradiation temperature, except for V±5Ti and V±5Nb. However, the hardening decreased with increasing irradiation temperature from 350°C to 400°C. The dislocation loops were observed by TEM after irradiation from 90°C to 200°C, while no void was observed at these irradiation temperatures. Positron annihilation spectroscopy (PAS) exhibited the nucleation of vacancy clusters in undersized binary alloys. The dislocation loop density increased with increasing irradiation temperature. It is considered that the irradiation hardening is mainly caused by dislocation loops. It has also been suggested that interstitial oxygen promote dislocation loop nucleation since interstitial oxygen and solute atoms interacted strongly and bound at around 200°C leading to enhanced nucleation of interstitial loops. Ó