In commercially available generation III and III+ PWR (pressurized water reactor) reactors, pressure of steam produced in steam generators varies in a relatively wide range from 5.7 to 7.8 MPa. Therefore, it is important to ask which value of steam pressure should be used for a specific unit, taking into account different location conditions, the size of the power system and conditions of operation with other sources of electricity generation.
The paper analyzes the effect of steam pressure at the outlet of a steam generator on the performance of a PWR nuclear power plant by presenting changes in gross and net power and efficiency of the unit for steam pressures in the range of 6.8 to 7.8 MPa. In order to determine losses in the thermal system of the PWR power plant, in particular those caused by flow resistance and live steam throttling between the steam generator and the turbine inlet, results concerning entropy generation in the thermal system of the power plant have been presented.
A model of a nuclear power plant was developed using the Ebsilon software and validated based on data concerning the Olkiluoto Unit 3 EPR (evolutionary power reactor) power plant. The calculations in the model were done for design conditions and for a constant thermal power of the steam generator. Under nominal conditions of the Olkiluoto Unit 3 EPR power unit, steam pressure is about 7.8 MPa and the steam dryness fraction is 0.997. The analysis indicates that in the assumed range of live steam pressure the gross power output and efficiency increase by 32 MW and 0.735 percentage point, respectively, and the net power output and efficiency increase by 27.8 MW and 0.638 percentage point, respectively.
In the case of all types of commercially available PWR reactors, water pressure in the primary circuit is in the range of 15.5−16.0 MPa. For such pressure, reducing the live steam pressure leads to a reduction in the efficiency of the unit. Although a higher steam pressure increases the efficiency of the system, it is necessary to take into account the limitations resulting from technical and economic criteria as well as operating conditions of the primary circuit, including the necessary DNBR (departure from nucleate boiling ratio) margin. For the above reasons, increasing the live steam pressure above 7.8 MPa (the value used in EPR units that have already been completed) is unjustified, as it is associated with higher costs of the steam generator and the high-pressure part of the turbine.

The aim of this paper is to make us aware of the limits of the numismatic documentation of Northern and Eastern Europe during the Early Middle Ages/the Viking Age. The sheer mass of material – almost 900,000 coins are recorded from finds along with numerous non-monetary silver artefacts – may induce us to think that everything is documented already, but at a closer scrutiny, this turns out to be wrong. Some regions and periods and some find categories are well covered by the material, others not. The paper presents a series of cases where a new find, a new technology (e.g. metal detector), a new methodological approach (e.g. die studies) or simply a more detailed study of the material brought new and unexpected insights. Some of the cases concern the coin production, others the coin circulation. Going beyond numismatics seen in isolation, the results inform us about the economic, political and social structures of the past society and thus highlight the contribution of numismatics to the study of history. In turn, these knowledge break-throughs open new paths of research and, significantly, make us aware of potential similar parallel cases of not yet recognized insights. This will help us to guide future research. In some cases, it would even be safe to extrapolate from the specific innovative case study to more general assumptions. In particular, the paper highlights danger of drawing conclusions from absence of evidence. Several examples are presented where the supposed lack of finds or of coin production turned out to be the result of inadequate research methods or technologies for finding the material in the ground. In other cases, the hazard of the discovery of a hoard changed the situation from absence or scarcity to abundance overnight. If conclusions are to be draw from absence of evidence, a minimum requirement would be to check that adequate research methods have been applied in order to ascertain that the absence is real and not the result of present day factors.

Western Ukraine arouses a high emotional charge of historical origin. There are a number of buildings and complexes in this area created since the 14th century, that are the witnesses of the Polish presence and our contribution to the culture of these lands. The monuments of sacred architecture and numerous military ones occupy a special place. In the short interwar period a number of structures and complexes that demonstrate a high level of design technique were created. Their current technical state is usually very bad. Our participation in restoring splendour to the witnesses of our, historical centuries-old presence, would be beneficial.