Brittle Strength of the VVER Pressure Vessel Steels under Operation Conditions

Complex of mechanical tests and fractographic studies of various sample types were conducted for VVER pressure vessel steels. The brittle fracture sources (origins) were revealed: “non-metallic inclusions” and “structural boundaries”. The computational-experimental technique for evaluation of the local normal stress parameter that characterizes strength of the origin was performed. Values of the local normal stressfor the “structural boundary” origin type was demonstrated to be decreasing after thermal and radiation embrittlement due to decreasing in cohesive strength of grain boundaries by virtue of thermo- and radiation- stimulated diffusion of the impurities to grains boundaries. Keywords: reactor pressure vessel, fractography, local normal stress, brittle fracture, origi

Case-control study of apoE gene polymorphism in young CHD patients and controls in the Serbian population

Apolipoprotein E displays polymorphism with three common alleles, e2, e3, and e4. The aim of this research was to determine apoE gene polymorphism in a group of healthy patients and a group of patients with CHD, and to reveal the relation between anthropometric and biochemical parameters and the apoE genotype. In CHD group significantly higher values of blood pressure, waist circumference, BMI and fat %, triglycerides, insulin (HOMA IR) and CRP were found. A statistically significant higher presence of the e3e4 genotype and e4 allele was detected in the CHD group. Statistically significant differences between waist circumference, BMI, insulin and HOMA IR were found between subjects with e3e3 and e3e4 genotypes

Einfluß der Zusammensetzung auf die Strahlenversprödung von Eisenlegierungen

The radiation embrittlement of the reactor pressure vessel is highly safety-relevant for VVER-type pressure vessels. The sensitivity against radiation embrittlement depends on the chemical composition of the pressure vessel steel. Using an irradiation experiment at surveillance positions in two Russian VVER 440-type reactors the effects of copper, phosphorus and nickel on the radiation embrittlement should be investigated. For that, eight mock-up alloys were selected. Their chemical composition varied between 0.015 and 0.42 % Cu, 0.002 and 0.039 % P, 0.01 and 1.98 % Ni, 0.09 and 0.37 % Si, and 0.35 and 0.49 % Mn. Charpy-V impact tests and tensile tests were performed with specimens machined from these alloys. The specimens were tested in the as-received state, in the irradiated state (fluence: 1x1019 and 8x1019 /cm2 [E>0.5 MeV]) an in the post-irradiation annealed state. In the as-received state, the alloys have a ferritic microstructure. Apart from Cu, the alloyed elements are solved in the matrix. Irradiation produces strong hardening and embrittlement. The effect increases with the Cu and P content. Ni causes an additional embrittlement. It is independent on the Ni concentration within the range of 1.1 to 2 % Ni and results in a shift of the ductile-brittle transition temperature of about 120 °C after a fluence of 1x1019 /cm2 by a flux of 4x1011 /cm2s. The shift does not depend on the Cu or P content. Furthermore the upper shelf energy is especially reduced by the Ni-rich alloys. For very low content of Cu and P these relations are not valid. The irradiation effect can be eliminated by annealing at 475 °C /100 h. For high content of Cu or P the recovery is incomplete, it remains a residue of 20 to 25 % of the irradiation effect. Ni has no influence on the recovery. Comparing the results of this study with the ones of the surveillance programmes of the VVER 440-type reactors, the alloys with low Ni content show the same irradiation behaviour as the weld metal. For the Ni rich alloys such well-walidated references are missing. The experiment is part of an extended research programme. It supposed to continue in order to gain information about the synergistic effects of these elements

Extended Analysis of VVER-1000 Surveillance Data.

Abstract not availableJRC.F-Institute for Energy (Petten

Fluence Rate Effects on Irradiation Embrittlement of Model Alloys.

Abstract not availableJRC.F-Institute for Energy (Petten

Fluence Rate Effects on Irradiation Embrittlement of Model Alloys

The Reactor Pressure Vessel (RPV) material of Nuclear Power Plants (NPP) is exposed to neutron irradiation during its operation. Such exposure generally induces degradation of the mechanical and physical properties of the materials: e.g. an increase of the ductile to brittle transition temperature (DBTT) and a decrease of the upper shelf impact energy. At a given irradiation temperature, dose and neutron spectrum, the sensivitity of materials to neutron irradiation depends on their chemical composition. In particular, elements like phosphorus, P, copper, Cu, and nickel, Ni play a key role in RPV steels. The effect of fluence rate on irradiation embrittlement of RPV materials is also a key issue for the ocrrect interpretation of accelerated data and surveillance data in view of reactor pressure vessel life assessment of nuclear reactors. Much effort was done in the last decades to tackle such issues and quite contradictory results have been obtained. Model alloys can successfully be used to study embrittlement mechanisms and the effect of fluence rate. A parametric study of the response to neutron irradiation of 32 different model alloys with systematic variation of elements (Ni from 0.004 to ~2 wt%, P from 0.001 to 0.039 wt%, Cu from 0.005 to ~1 wt%) was completed by some members of the European Network AMES. The irradiation of the 32 model alloys took place in the LYRA rig at the HFR of the JRC, Petten, The Netherlands. Some model alloys were also irradiated in commercial reactors, namely in Rovno Nuclear Power Plant (NPP), Ukraine, and Kola NPP in Russia. Data available on these model alloys are presented and analysed in this paper, proving to be very important for the study of fluence rate effect.JRC.F.4-Nuclear design safet

Irradiation Temperature, Flux and Spectrum Effects

Although great progress has been made in understanding the irradiation behaviour of reactor pressure vessel (RPV) steels, many aspects are still not fully understood. Large amount of data has been generated for understanding the effects of different irradiation conditions on material properties. The data needed for the long term operation of RPVs is almost always created by accelerated irradiations in test reactors, and due to insufficient knowledge on the damage interaction between the material and the high energy neutrons the potential bias of the conclusions on material properties in non-accelerated irradiation conditions can not be excluded. Important parameters for the extrapolation of results from accelerated irradiations to typical power irradiation conditions are the irradiation temperature, the neutron flux and the neutron spectrum. In particular, the effect of neutron flux on embrittlement behaviour is considered a complex phenomenon, and it seems to be dependent on the alloy composition, the neutron fluence range and the irradiation temperature. This paper will present the current knowledge on temperature, flux and spectrum effects, based on a recent literature survey and other relevant publications on the subject. It will explore the implications these effects may have for the safety evaluation of aged RPVs, in special for those exposed to long irradiation periods.JRC.DDG.F.5-Safety of present nuclear reactor

Study of PRIMAVERA Steel Samples by a Positron Annihilation Spectroscopy Technique

In the present article, a positron annihilation spectroscopy investigation of VVER-440/230 weld materials is discussed. Important characteristics of metals such as Fermi energy, concentration of electrons in the conduction band, size and concentration of defects were experimentally determined for three model materials with higher level of copper (0.16 wt.%) and phosphorus (0.027-0.038 wt.%). The impact of neutron irradiation and subsequent annealing on crystal lattice parameters was investigated. The experiments complement the published PAS studies of the radiation treated VVER materials as well as previous experiments on PRIMAVERA materials with the angular correlation of positron annihilation radiation (PAS-ACAR) measurements. The availability of the experimental reactor to prepare strong 64Cu positron sources provided for unique experimental conditions, such as good resolution of spectra (0.4 mrad) and reasonable short time of measurement (36hours). The present paper aims to contribute to further understanding of RVP steels behavior under irradiation conditions as well as annealing recovery procedures, which have already been applied at several VVER NPP units in Europe.JRC.F.5-Safety of present nuclear reactor

Einfluß der Zusammensetzung auf die Strahlenversprödung von Eisenlegierungen

The radiation embrittlement of the reactor pressure vessel is highly safety-relevant for VVER-type pressure vessels. The sensitivity against radiation embrittlement depends on the chemical composition of the pressure vessel steel. Using an irradiation experiment at surveillance positions in two Russian VVER 440-type reactors the effects of copper, phosphorus and nickel on the radiation embrittlement should be investigated. For that, eight mock-up alloys were selected. Their chemical composition varied between 0.015 and 0.42 % Cu, 0.002 and 0.039 % P, 0.01 and 1.98 % Ni, 0.09 and 0.37 % Si, and 0.35 and 0.49 % Mn. Charpy-V impact tests and tensile tests were performed with specimens machined from these alloys. The specimens were tested in the as-received state, in the irradiated state (fluence: 1x1019 and 8x1019 /cm2 [E>0.5 MeV]) an in the post-irradiation annealed state. In the as-received state, the alloys have a ferritic microstructure. Apart from Cu, the alloyed elements are solved in the matrix. Irradiation produces strong hardening and embrittlement. The effect increases with the Cu and P content. Ni causes an additional embrittlement. It is independent on the Ni concentration within the range of 1.1 to 2 % Ni and results in a shift of the ductile-brittle transition temperature of about 120 °C after a fluence of 1x1019 /cm2 by a flux of 4x1011 /cm2s. The shift does not depend on the Cu or P content. Furthermore the upper shelf energy is especially reduced by the Ni-rich alloys. For very low content of Cu and P these relations are not valid. The irradiation effect can be eliminated by annealing at 475 °C /100 h. For high content of Cu or P the recovery is incomplete, it remains a residue of 20 to 25 % of the irradiation effect. Ni has no influence on the recovery. Comparing the results of this study with the ones of the surveillance programmes of the VVER 440-type reactors, the alloys with low Ni content show the same irradiation behaviour as the weld metal. For the Ni rich alloys such well-walidated references are missing. The experiment is part of an extended research programme. It supposed to continue in order to gain information about the synergistic effects of these elements