[en] Accident analyses have to show that general safety functions, as are safe shutdown and long term subcriticality of the reactor, residual heat removal and limitation of radioactive releases and shielding, are ensured for operational transients at any time. In addition to the control of operational transients, measures are foreseen to mitigate the consequences of anticipated transients without scram (ATWS) as an example of beyond design basis accident. The safety objectives for ATWS are to ensure long term subcriticality of the reactor and heat removal from the reactor coolant system. The dependence of initial and boundary conditions on the purpose of analyses is discussed. Conservative cases of operational transients and of accidents are described. Examples are given of acceptance criteria for the general safety function performance. (J.B.)

[en] Common Cause Failures (CCF) have been an issue of safety consideration in nuclear safety since a long time. For the design of the European Pressurised Reactor (EPR) probabilistic safety goals in conjunction with the limit set by CCF on failure probability that can be achieved by redundancy led to the requirement to fulfil vital safety functions by functionally diverse systems. The probabilistic safety analysis (PSA) which was performed for EPR takes into account CCFs which are modelled using the beta-factor model of the European Utility Requirements (EUR). The PSA shows that the probabilistic safety goal for core damage frequency - CDF < 10^-5/year - is met with sufficient margin. In addition to the modelling of CCF in the PSA a deterministic CCF analysis is being performed. It is a safety function based approach on component level analysing frontline and backup systems with respect to common components or type identical components. It ensures that diverse safety functions are fulfilled by systems being sufficiently diverse including all necessary support systems. Components are identified where further diversification or additional defences against CCF are required. (orig.)

[en] In this paper possibilities of extending supply mission of nuclear heating stations by provision of both hot water for district heating and steam for industrial consumers are studied. Based on applying a method developed for hot water generation only, trends in the heat-engineering design of a nuclear heating station designated to cogeneration of hot water and process steam are derived. Results of calculations show that in the case of larger amounts of process steam to be generated modifications of the reactor of the AST-500 type nuclear heating station developed in the USSR for hot water generation only would have to be provided. Lower amounts of steam might be provided by slightly increasing core pressure with no changes in the design of the primary coolant circuit. (author)

[en] One of the possibilities of nuclear heat supply are nuclear district-heating plants (NDHP). In addition to ensuring high safety, investigations on NDHP design have also to pay attention to economical problems. A method of optimizing thermal parameters in the three main circuits of an NDHP is presented, which is based on the fact that both the power required from the power station and the heat supply temperatures of the district heating system into which the plant will be introduced are known. As the objective function of optimization minimization of annual variation of expenses with respect to a basic version of design is formulated. Preliminary results of optimizing calculations are presented. The method described should be appraised as a preliminary contribution to NDHP design. Moreover, possibilities of fitting the AST-500 plant to higher heat supply temperatures are discussed. It is shown that, within certain limits, the hot water heat supply temperature might already by raised inside the NDHP. (author)

[en] Nuclear heating stations provide one possibility of supplying nuclear heat. They are uniquely intended for heat supply. The well-known Soviet nuclear heating station AST-500 with an output temperature of 150 ⁰C in the network pipes is below the value designed for some heat supply systems in the GDR. On the basis of a general method applicable to the choice of optimum parameters, proposals are placed for optimally matching design and layout of the AST-500 station to higher output temperatures. Minimization of the difference in expenses between the modified version and the well-known basic version of the AST-500 station has been used as the objective function of optimization. (author)

[en] New reactor designs aim to reach a higher safety level than the existing nuclear power plants. This requires very reliable safety systems. Reliability, achievable by redundancy is limited by common cause failures (CCF). Therefore, diversity needs to be introduced in the design of safety systems or safety functions. A systematic deterministic approach, called 'Deterministic Common Cause Failure Analysis ', has been developed which is not only restricted to the front-line safety system part but analyzes the safety systems including their necessary support system functions to be sufficiently diverse. (authors)

[en] The passivation of Si by Al₂O₃/ZnO stacks, which can serve as passivated tunneling contacts or heterojunctions in silicon photovoltaics, was investigated. It was demonstrated that stacks with Al₂O₃ thicknesses >3 nm lead to lower surface recombination velocities (S_eff,max < 4 cm s⁻¹) on n- and p-type Si than single-layer Al₂O₃ films for a wide range of ZnO thicknesses and irrespective of Al-doping of the ZnO. Stacks with an Al₂O₃ thickness of 1–2 nm were found to combine reasonable surface passivation (S_eff,max = 100–700 cm s⁻¹) with sufficiently high tunneling current densities (10–300 mA cm⁻² at 700 mV). (fast track communication)