Protein-ion Interactions: Simulations of Bovine Serum Albumin in Physiological Solutions of NaCl,KCl and LiCl

Specific interactions that depend on the nature of electrolytes are observed when proteins and other molecules are studied by potentiometric, spectroscopic and theoretical methods at high salt concentrations. More recently, it became clear that such interactions may also be observed in solutions that can be described by the Debye-Hückel theory, i.e., at physiological (0.1 mol dm⁻³) and lower concentrations. We carried out molecular dynamics simulations of bovine serum albumin in physiological solutions at T=300 and 350 K. Analysis of the simulations revealed some differences between LiCl solutions and those of NaCl and KCl. The binding of Li⁺ ions to the protein was associated with a negative free energy of interaction whereas much fewer Na⁺ and K⁺ ions were associated with the protein surface. Interestingly, unlike other proteins BSA does not show a preference to Na⁺ over K⁺. Quantum chemical calculations identified a significant contribution from polarisation to the hydration of Li⁺ and (to a lesser degree) Na⁺, which may indicate that polarisable force-fields will provide more accurate results for such systems.     

Crack initiation and arrest in a pressurized thermal shock test for a model pressure vessel made of VVER-440 reactor pressure vessel steel

A joint pressure vessel integrity research programme involving three partners is being carried out during 1990–1995. The partners are the Central Research Institute of Structural Materials “Prometey” from Russia, IVO International Ltd (IVO) from Finland, and the Technical Research Centre of Finland (VTT). The main objective of the research programme is to increase the reliability of the VVER-440 reactor pressure vessel safety analysis. This is achieved by providing material property data for the VVER-440 pressure vessel steel, and by producing experimental understanding of the crack behaviour in pressurized thermal shock loading for the validation of different fracture assessment methods. The programme is divided into four parts: pressure vessel tests, material characterization, computational fracture analyses, and evaluation of the analysis methods. The testing programme comprises tests on two model pressure vessels with artificial axial outer surface flaws. The first model vessel had circumferential weld seam at the mid-length of the vessel. A special embrittling heat treatment is applied to the vessels before tests to simulate the fracture toughness at the end-of-life condition of a real reactor pressure vessel. The sixth test on the first model led to crack initiation followed by arrest. After the testing phase, material characterization was performed. Comparison of calculated and experimental data generally led to a good correlation, although the work is being continued to resolve the discrepancies between the measured initiation and arrest properties of the material.     

Descriptive characteristics of different types of test for irradiation embrittlement

Within the IAEA coordinated programme on optimizing of reactor pressure vessel surveillance programmes and their analysis, phase 3, a specially tailored radiation sensitive correlation monitor material, a Japanese steel plate with code designation JRQ, a French forging material (FFA) and a Japanese forging material (JFL) were selected for the investigations to be carried out in Finland.Based on the evaluation of the experimental results it was demonstrated that dynamic fracture toughness transition shift is equivalent to the Charpy-V shift, but the static fracture toughness transition shift may be considerably larger than the dyanamic shift. Thus, Charpy-V is not suitable for estimating the static fracture toughness transition shift.These findings have a strong impact upon the design of future surveillance programmes.     

Role of lubrication oil in particulate emissions from a hydrogen-powered internal combustion engine

Recent studies suggest that trace metals emitted by internal combustion engines are derived mainly from combustion of lubrication oil. This hypothesis was examined by investigation of the formation of particulate matter emitted from an internal combustion engine in the absence of fuel-derived soot. Emissions from a modified CAT 3304 diesel engine fueled with hydrogen gas were characterized. The role of organic carbon and metals from lubrication oil on particle formation was investigated under selected engine conditions. The engine produced exhaust aerosol with log normal-size distributions and particle concentrations between 10(5) and 10(7) cm(-3) with geometric mean diameters from 18 to 31 nm. The particles contained organic carbon, little or no elemental carbon, and a much larger percentage of metals than particles from diesel engines. The maximum total carbon emission rate was estimated at 1.08 g h(-1), which is much lower than the emission rate of the original diesel engine. There was also evidence that less volatile elements, such as iron, self-nucleated to form nanoparticles, some of which survive the coagulation process.     

Experience of irradiation embrittlement in the Loviisa reactor pressure vessels

The water gap between the wall and the core of the RPV (Reactor Pressure Vessel) in a VVER-440 plant is small compared with typical Western type LWR₅. The neutron fluence on the RPV wall is, consequently, much higher in a VVER-440 plant. In older VVER-440 plants the material of the RPV, especially the horizontal core weld, contains so much impurities (P- and Cu-content) that the irradiation embrittlement has become a problem. On bases of fracture mechanics analyses in Loviisa, IVO has been forced to make several measures to ensure safe operation of the plants. According to IVO's current understanding, both plants may be in operation for the design life without annealing of the RPVs.     

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. A 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, especially for those exposed to long irradiation periods.     

E-mail classification with machine learning and word embeddings for improved customer support

Neural Computing and Applications - Classifying e-mails into distinct labels can have a great impact on customer support. By using machine learning to label e-mails, the system can set up queues...     

Neutron Embrittlement of WWER Reactors: EC-Supported Projects

Results of the implementation of programs on the evaluation of the service life of reactor pressure vessels of NPPs are considered with the account of neutron embrittlement. Data on strength of WWER-440 reactor pressure vessels with a high and moderate content of detrimental impurities (copper and phosphorus) have been analyzed. For the welds of WWER-1000 reactor, drawbacks in the manufacture, dosimetry, and test procedures of surveillance specimens are shown. To ensure safe operation of reactor pressure vessels, new projects have been undertaken, focusing on the effect of neutron embrittlement of steel on the integrity of structures and on advanced experimental methods of studying material strength.     

Neutron embrittlement of VVER reactor pressure vessels—recent results, open issues and new developments

Decisions regarding the verification of design plant lifetime involve a determination of the component and circuit condition. Neutron embrittlement of reactor pressure vessels (RPV) becomes a crucial consideration for continued safe plant operation. Since 1991, the European Commission (EC) has financed a significant number of projects in this area, in particular through the TACIS and PHARE programmes. In Nuclear Safety support programmes the countries mainly concerned are Russia, Ukraine, Armenia, and Kazakhstan for the TACIS programme, and Bulgaria, Czech Republic, Hungary, Slovak Republic, Lithuania, Romania and Slovenia for the PHARE programme. The corresponding results of these projects on neutron embrittlement have contributed to a better understanding of the available data and their uncertainties. Recent confirmations of the irradiation temperatures of the surveillance specimens in the operating VVER nuclear power plants show that the surveillance specimens can be used further for the validation of the current and the expected neutron embrittlement. Taking into account the latest results as a baseline for the development of the necessary material data to be used for upgraded RPV integrity assessment, two new TACIS projects are being launched, jointly with Russia and Ukraine, whose scope is:

• Upgrading the surveillance databases.

• Acquisition of new impact test and toughness results on reconstituted surveillance specimens, including the evaluation of the Mater Curve Approach.

• Further validation tests of the shape of the fracture toughness curve and the base and weld metal and characterization of the cladding.

• Preparation of some selected upgraded RPV integrity assessments, with insights on the latest approved methodology.

The paper summarizes the major conclusions of the recent completed EC projects, reviews the remaining major open issues in the field of reliable determination of fracture toughness properties of the operating VVER RPVs, and details the scope of the new projects.