Views of TAGSI on effects of neutron irradiation on ductile tearing in ferritic steels

The paper reviews information pertaining to effects of neutron irradiation on “upper-shelf” Charpy impact behaviour and on elastic/plastic fracture mechanics characterising parameters, again for “upper shelf” conditions, in which the initiation and early growth of a crack involve ductile tearing. The hardening and associated reduction in strain-hardening capacity induced by irradiation gives rise to a decrease in Charpy upper shelf energy. Effects on J-based parameters are more complicated. The material resistance parameters tend to increase for low dose, but decrease at high dose, when the decrease in crack-tip ductility outweighs the effect of hardening. High doses can produce “fast shear” fracture, which propagates rapidly and is therefore more likely to induce brittle cleavage fracture. The situation is exacerbated if the irradiation also promotes inter-granular segregation and fracture, hence reducing the local brittle fracture stress. For the levels of irradiation experienced by the types of UK civil reactors in operation, no fracture instability is expected to arise as a result of ductile fracture mechanisms alone.     

The effect of warm prestressing on proof tested pressure vessels

The beneficial effects of warm prestressing of cracked pressure vessels using a proof test are investigated using experimental and theoretical evidence. An approach based on the reloading capacity is proposed which is dependent on only two parameters: the extent of prior unloading and the fracture toughness. A simple lower bound failure criterion is given which avoids most of the uncertainties in input data which are usually associated with integrity assessments. The approach is validated using available experimental failure data.     

Views of TAGSI on the effects of gamma irradiation on the mechanical properties of irradiated ferritic steel reactor pressure vessels

The paper reviews and analyses the effects of gamma irradiation dose on the properties of ferritic steels used in reactor pressure vessels (RPVs). It explains factors that affect the embrittlement of a RPV steel induced by combinations of fast neutrons, thermal neutrons, and gamma irradiation.

TAGSI were asked to consider the effects of gamma irradiation dose on the properties of steels used in reactor pressure vessels. TAGSI endorsed the use of the MCBEND code to calculate gamma fluxes and energetic gamma ray displacement cross-sections calculated using either Baumann or Alexander methods. TAGSI endorsed the calculation of the materials property changes due to an additional gamma dose using trend curves based on empirical correlation to neutron-induced damage (where k_γ1±0.25).     

Views of TAGSI on the principles underlying the assessment of the mechanical properties of irradiated ferritic steel Reactor Pressure Vessels

The principles are reviewed which underlie trend curve development for irradiated ferritic Reactor Pressure Vessel steels where the dominant embrittlement mechanism is cluster hardening. The extent to which the form of the equations employed reflect the underlying physical mechanism is assessed.     

TAGSI views on aspects of crack arrest philosophies for pressure vessels with thicknesses up to 100 mm

As part of its ongoing technical programme the UK nuclear industry's Technical Advisory Group on Structural Integrity (TAGSI) was asked to comment on three issues concerning use of crack arrest arguments in structural integrity assessments for pressure vessel applications. The paper summarises the content of the TAGSI discussions and conclusions.     

Oxygen efficiency with regard to carbon capture

Carbon capture is often discussed in the literature with the sole focus on power processes, despite the fact that carbon dioxide emissions from other sources are just as relevant for the impact on the atmosphere. Furthermore, some carbon capture methods are relatively inefficient when applied to power production processes. Carbon capture should preferably be performed where the cost is as low as possible, i.e. not necessarily from power production processes. As an example, carbon capture using combustion with pure oxygen is far more energy efficient if it is used together with lime kilns or cement kilns than together with power production processes. A new concept termed “oxygen efficiency” is introduced in this paper. It describes the amount of carbon dioxide that can potentially be captured per unit of oxygen. As such, the oxygen efficiency quantifies the value of a certain unit of oxygen for carbon capture reasons. The base concept is that the energy penalty for the production of one part of oxygen is the same no matter where it is produced; hence, if this unit of oxygen can be used to capture more carbon dioxide, it is more efficient. Typically, the oxygen efficiency would be five times greater for carbon capture when utilising pure oxygen together with cement kilns rather than together with methane-fired power plants. Furthermore, the concept of oxygen efficiency illustrates the importance of considering how carbon capture methods can be utilised in the most efficient way, in addition to evaluating which carbon capture method is the most suitable for a particular technology.     

Thermal comfort temperatures world-wide - the current position

The development of the adaptive approach to thermal comfort is reviewed from 1970 to 1995. It is argued that the adaptive approach is likely to yield useful standards for thermal comfort world-wide. These standards would take into account both climate and culture, and would need less energy than current standards.     

Possibilities of improving the efficiency of power generation with regard to electrolytic water splitting

The efficiency of power generation has a considerable influence on the upper limit of the total efficiency of electrolytic water splitting. This paper deals with the energetic potential of power generation processes and therefore with the water electrolysis processes. In the investigations reported here, it was assumed that the heat source is always the same (high-temperature nuclear reactor). For comparing thermochemical or hybrid water splitting cycles and water electrolysis, the upper limit of process temperatures must be comparable, too. Therefore high-temperature processes for power generation have been investigated. A detailed energy and exergy balance is presented for the following cycles: (1) steam turbine cycles; (2) helium gas turbine cycles; (3) combined gas/steam turbine cycles. For these different processes an exergy analysis was performed in order to localize the process units, which make a considerable contribution to the decrease in total efficiency.     

Dishwashing behaviour of European consumers with regard to the acceptance of long programme cycles

Since the introduction of the energy label for household dishwashers in the EU, manufacturers have been incentivised to reduce resource consumption and increase the energy efficiency of their appliances. Technological progress has led to very efficient programmes with cleaning cycles of 3 to 4 h or longer. The European Commission recently initiated a revision of the energy label and Ecodesign requirements, leading to their adjustment to the state of the art and to actual usage patterns. The University of Bonn was tasked with investigating dishwashing habits in Europe. An online survey was conducted in 11 countries of the EU with more than 5000 participants. The survey focused on the choice of programme, attitudes towards energy-saving programmes and practices and the willingness to apply them. It appears that consumers are willing to apply energy-saving practices and to use energy-saving programmes, but the acceptance of long cycles that take more than 2 h is low, which stands in contradiction to the fact that 19% of all dishwashing cycles are run in the Eco programme, which takes more than 2 h in most cases. The percentage of people who understand that long cycles can be energy-efficient is smaller than the percentage of those who do not believe this. The statements of the participants are contradictory regarding the importance of saving energy and of programme duration. The results of the survey point out the importance of better consumer education and better communication by manufacturers, consumer organisations and legislation.     

Some challenges in the treatment of residual stress in flaw tolerance calculations—A TAGSI view

The UK Technical Advisory Group on the Structural Integrity of Nuclear Plant (TAGSI) has recently reviewed the methodologies for combining residual stresses with primary stresses. The review was focused on those situations where secondary stresses are large compared to the primary stresses and where, in the case of ductile materials such as stainless steel, procedures predict low margins of safety, contrary to perception and practical experience.     

The potential of energy utilization from logging residues with regard to the availability of ashes

This paper evaluates the conditions under which the availability of ashes suitable for recycling limits the expansion of a sustainable energy harvest of logging residues from the forest. One of the major potentials that could increase the use of bioenergy in Sweden is the use of logging residues—tops and branches—that are now left behind in the forest. To avoid nutrient depletion and increased acidification, wood ashes should be recycled to the forest ecosystem. An increased use of logging residues will lead to a higher demand for recyclable ashes. The harvest of logging residues will probably be restricted if the available amount of ashes is less than the demand. A model is developed for the relation between the energy potential of the logging residues that could be utilized, the loss of nutrients in the technical chain, the available amount of wood ash from other sectors, and the level of nutrient compensation in the forest. The results indicate that the availability of ashes suitable for recycling will not limit the expansion of energy from logging residues if the loss of nutrients in the technical chain and the level of nutrient compensation are restricted. Actions in order to make this possible are proposed.     

Experimental investigation of melting heat transfer with regard to different geometric arrangements

In the present study melting experiments, performed with different geometric test configurations, are reported. The investigation encompasses the melting process adjacent to a heated vertical surface and inside a vertical as well as horizontal heated cylinder. All studied processes show common features and can be described by two-regime models. In the first stage of the process the conduction regime is valid, directly followed by a quasi-steady convection regime which can be described by a correlation of the form Nu = f(Ste, Ra). An appropriate transition criterion allows for the transition point between both regimes.     

Optimum heating of pressure components of steam boilers with regard to thermal stresses

A method for determining time–optimum fluid temperature changes is presented. In contrast to current standards, stepwise fluid temperature changes are allowed. The optimum fluid temperature changes are assumed in the form of a simple time function. It is possible to increase the fluid temperature stepwise, and then the fluid temperature can be increased with a constant rate at the beginning of the heating process. The permissible rates of the fluid temperature change determined by the proposed method are smaller than those obtained by boiler standards. But, due to the abrupt increase in fluid temperature, the heating time of a thick-walled component is of the same order as in the case of calculations according to EN 12952-3 European Standard. However, the total circumferential stresses on the edge of the hole do not exceed the allowable value.     

Renewable energy benefits with conversion of woody residues to pellets

In the frame of an Interreg IIIC Network-Operation named RegEnergy, that unites 18 partners from 11 countries of Europe, the feasibility of using the woody by-products for heating purpose in a typical Mediterranean region was investigated. Focusing on the Abruzzo Region as representative sample area, it came out that a significant amount of the above mentioned renewable energetic material is annually available as a consequence of well-consolidated and economically significant agro-industrial activities, forest maintenance and industrial wood production and transformation. In particular, it was found that the total amount of woody residues, as dry substance, are more than 700 kt/a, with 30% resulting from pruning activities related to the cultivation of about 360 km² of vineyards and 450 km² of olive-groves; these residues are concentrated in the hilly part of the region close to the Adriatic sea coast. Starting by this pleasant situation, the feasibility of a properly localized wood pellets production plant was supported by both the economic and energetic analysis. Additional suggestions related to optimal plant localization and to the best use of the woody pellets as substitute of natural gas for heating purposes were reported along with the positive impact of the whole action on the quality of the environment and on the recovery of soil fertility.     

Evaluation of sodium incipient superheat measurements with regard to the importance of various experimental and physical parameters

The published results of the various laboratories on the parameters having an influence on superheat are not definite. There has even been inconsistent and conflicting experimental evidence on the effect of some parameters.The most consistent agreement in the trend is seen in the influence of oxide impurity and gas entrainment. In both cases superheat decreases with increasing gas entrainment and oxide level.The most inconsistent and conflicting experimental evidence concerns the effect of heat flux and of temperature ramp. The data of bulk superheat as far as the trend is concerned are in good agreement. The bulk superheat definitely decreases with increasing velocity. An influence of the heating wall material on the superheat is uncertain. Experiments on materials compatible with sodium did not exhibit significant effects. Most of the experiments in which the influence of the operation time has been observed were short time tests. It is supposed that the effect of operating conditions was masked by the degassing of the heating surface during heating up or boiling. There is experimental evidence that for given test conditions a characteristic threshold superheat range is not exceeded. The threshold superheat level is presumably determined by the heating surface finishing, the oxide level and the gas loading of the sodium.A general evaluation of the results of loop experiments shows an average value of superheat for technically clean sodium of 80 ± 30°C (O₂-impurity of about 5–10 ppm) and for sodium with impurity of about 40 ppm of about 25 ± 20°C.     

关于编制"十五"节能规划的思考

1总论在过去的20年里,中国经济保持快速增长,而能源消费的增长速度却远远低于经济增长速度,究其原因,中国始于80年代初期的有计划、有组织开展的节能工作起了巨大作用,其中节能规划的制定实施更是功不可没。中国节能规划的实施使得中国能以较少的能源投入支撑了中国经济持续稳定的增长,并且对提高经济效益,推进技术进步,减少环境污染等方面也起了极其重要的作用。未来几十年内,中国经济仍将保持上升的势头,未来中国的能源（尤其是优质能源）需求也将持续上升;而随着人们对因能源使用而导致的局部地区乃至全球环境问题关注程度的…     

Finite element modeling of HIC propagation in pipeline steel with regard to experimental observations

In this research, hydrogen induced cracking (HIC) phenomenon in pipeline steel has been investigated by finite element modeling (FEM) with the help of experimental observations. Abaqus software has been utilized to model the crack. To this, first an API 5L X70 pipeline steel was electrochemically charged by hydrogen for 8 h to create different types of HIC cracks. Then, SEM was used to observe different types of hydrogen cracks. Based on the observations, most of HIC cracks were observed at the center of cross section where center segregation of some elements occurred. The results showed that HIC cracks propagated in stepwise, sinusoidal, straight and disordered manner. Moreover, HIC crack nucleated from a point with high stress concentration factor which was between non-metallic inclusion or void and metal matrix. The initiated micro-cracks from two neighbor inclusions link together to form a long HIC crack. Based on the experimental observations and FEM modeling, it was concluded that the driving force for the HIC crack propagation is the presence of hydrogen at the crack tip after it is initiated. Crack tip usually acts as a very small void and the combination of hydrogen atoms makes a high pressure which propel the crack forward. Moreover, the HIC crack propagation path was predicted by fracture mechanics approach showing that the J-integral had its maximum amount when the HIC crack tended to propagate horizontally.     

Experimental investigation of pulsating heat pipe performance with regard to fuel cell cooling application

A pulsating heat pipe (PHP) is a closed loop, passive heat transfer device. Its operation depends on the phase change of a working fluid within the loop. Design and performance testing of a pulsating heat pipe was conducted under conditions to simulate heat dissipation requirements of a proton exchange membrane (PEM) fuel cell stack. Integration of pulsating heat pipes within bipolar plates of the stack would eliminate the need for ancillary cooling equipment, thus also reducing parasitic losses and increasing energy output. The PHP under investigation, having dimensions of 46.80 cm long and 14.70 cm wide, was constructed from 0.3175 cm copper tube. Heat pipes effectiveness was found to be dependent upon several factors such as energy input, types of working fluid and its filling ratio. Power inputs to the evaporator side of the pulsating heat pipe varied from 80 to 180 W. Working fluids tested included acetone, methanol, and deionized water. Filling ratios between 30 and 70 percent of the total working volume were also examined. Methanol outperformed other fluids tested; with a 45 percent fluid fill ratio and a 120 W power input, the apparatus took the shortest time to reach steady state and had one of the smallest steady state temperature differences. The various conditions studied were chosen to assess the heat pipe's potential as cooling media for PEM fuel cells.     

Distributed energy resources and benefits to the environment

The recently released report of the International Energy Outlook (IEO2009) projects an increase of 44% in the world energy demand from 2006 to 2030, and 77% rise in the net electricity generation worldwide in the same period. However, threatening in the said report is that 80% of the total generation in 2030 would be produced from fossil fuels. This global dependence on fossil fuels is dangerous to our environment in terms of their emissions unless specific policies and measures are put in place. Nevertheless, recent research reveals that a reduction in the emissions of these gases is possible with widespread adoption of distributed generation (DG) technologies that feed on renewable energy sources, in the generation of electric power. This paper gives a detailed overview of distributed energy resources technologies, and also discusses the devastating impacts of the conventional power plants feeding on fossil fuels to our environment. The study finally justifies how DG technologies could substantially reduce greenhouse gas emissions when fully adopted; hence, reducing the public concerns over human health risks caused by the conventional method of electricity generation.