[en] The International Conference on Nuclear Power Performance and Safety, organized by the International Atomic Energy Agency, was held at the Austria Centre Vienna (ACV) in Vienna, Austria, from 28 September to 2 October 1987. The objective of the Conference was to promote an exchange of worldwide information on the current trends in the performance and safety of nuclear power and its fuel cycle, and to take a forward look at the expectations and objectives for the 1990s. This objective was accomplished through presentation and discussion of about 200 papers at the Conference. This is volume 4 of the conference proceedings. All the presentations in it were divided into 3 sessions: Nuclear safety experience and safety assessment trends (16 papers); Safety and severe accidents (18 papers); Safety improvements in design and operation (16 papers). The 11 poster presentations are also included in this volume. A separate abstract was prepared for each of these presentations. Refs, figs and tabs

[en] Safety practices adopted in Italy are based on two general principles: integration of safety requirements with health protection objectives; and extensive 'defence in depth', which includes redundancy and diversity of physical barriers, of types of safety measures and of types of safety criteria (deterministic and probabilistic). In this framework severe accidents are considered for introduction into safety analyses and external emergency planning in order to implement an additional barrier, founded on management of severe accidents, against uncontrolled releases of radioactivity. The criterion dealing with severe accidents, formulated in June 1985 and widely discussed, can be stated thus: ''It is considered realistic to assure, by additional accident management provisions, with a confidence level of the order of 95%, that external releases of iodine and caesium, in situations otherwise leading to uncontrolled severe accidents, be limited within 0.1% of core inventory.'' This criterion is now in a final phase of trial-implementation in Italian plants. The combination of the Italian design criteria for design basis accidents and core melt prevention and of the above stated criterion concerning severe accidents can be viewed as a more realistic alternative to an unrestricted 'safety goal' approach to safety. This alternative consists of establishing limited quantitative goals based on sound knowledge, to be extended as knowledge grows, and in critically and responsibly submitting to engineering judgement, as a final verification, what is left beyond such limited goals, in the unlimited field of conceivable possibilities. The present status of the implementation in Italy of practices concerning severe accidents is discussed in the paper with reference both to accident management within the plants and to external emergency planning. (author). 3 refs, 1 fig

[en] The paper evaluates the situation with regard to the development of nuclear power in the USSR following the accident at the Chernobyl nuclear power plant. It is stated that the development of nuclear power in the USSR will continue with due regard to the lessons learnt from the Chernobyl tragedy. In the present circumstances renewed and increased attention is being paid to safety, which even before was of prime importance in the development of nuclear power. This attention is focused on increasing the quality of operation, adopting the necessary technical measures at existing plants, reviewing and improving safety requirements and achieving more efficient and better adapted functioning of the system of State supervision. Specific measures are described which have been undertaken or are being undertaken to improve the safety of nuclear power plants with RMBK reactors and plants with WWER-1000 reactors which are likely to serve as the basis for the further development of nuclear power in the USSR. Consideration is given to reactors with an increased level of safety. (author). 1 ref

[en] The paper gives an overview of the probabilistic safety studies performed in Ente Nazionale per l'Energia Elettrica's NPPs now being constructed or designed (Alto Lazio BWR and Progetto Unifacato Nucleare (PUN) PWR). This activity proved quite useful in ascertaining compliance with the predetermined safety objectives, and as a tool for identification of the main corrective actions required. The approach was then used to evaluate the safety level of the plants in operation (Latina Magnox, Caorso BWR, Trino PWR). The experience gained from these plants is almost complete and provides a few useful indications on the possible use of this tool as a source of additional information that is not available from other sources. Every NPP has its own frequency of core damage that depends on the peculiar aspects of the station under examination. A comparison of the results from different plants should be interpreted taking into consideration the completeness of the analysis and the methodology used. (author). 12 refs

[en] The United States Department of Energy program of severe accident technology has grown with the realization of the importance of severe accidents to the safety and survival of nuclear power. Today, it is comprised of the Three Mile Island (TMI) accident evaluation program, the Organisation for Economic Co-operation and Development Loss-of-Fluid Test (LOFT) program, and several experimental studies designed to reduce uncertainties to levels sufficient to support resolution of risk significant severe accident issues. In the TMI program, 10 core bores have recently been taken from the destroyed core, for the first time providing a look at what is contained beneath the cavity discovered in the upper portion of the original core region. A lens-shaped homogeneous volume of previously molten core material is generally enclosed in a 10-15 cm thick layer of metal-fuel agglomerate located above standing fuel rods in the lower regions of the core. An international program has been formed to share in various sample examinations and in an analytical benchmark study of the accident. The final LOFT experiment subjected a fuel bundle to the first stages of a V-sequence accident and achieved fuel temperatures above 2100 K for 4.5 minutes. The resulting release and transport of fission products and aerosols were measured. The damaged fuel is now being prepared for examination. The combined results of this controlled and instrumented experiment will provide a picture of events as they occurred in the early stages of the TMI-2 accident. In a supporting study on fission product revaporization, the physical, chemical, and transport properties of species that are likely to dominate the transport process are measured, new species, important to fission product transport such as the complex CsI-CsOH, are being discovered and studied and the resulting data is being correlated for use in severe accident codes. (author). 10 ref, 1 fig., 2 tabs

[en] Poster presentation

[en] The paper summarizes the recent comprehensive reassessment of reactor risk performed by the United States Nuclear Regulatory Commission (NRC), as presented in Draft NUREG-1150: The Reactor Risk Reference Document. Draft NUREG-1150 provides results of risk analyses for five different light-water reactors in the United States of America. For the plants analyzed, this document describes (1) the major factors related to internally initiated events (excluding fires, floods, and earthquakes) that contribute to severe core damage, (2) the frequencies and related uncertainty ranges of severe core damage events, (3) the major factors and severe accident phenomena that could lead to containment failure (and particularly early containment failure), (4) the conditional probabilities and uncertainty ranges of early containment failure, (5) the sequences and risks of severe accidents, including the sensitivity of these risks to factors such as evacuation of sheltering measures, (6) comparisons of the risks with NRC safety goals, and (7) cost and risk-reduction analysis of plant-specific measures that could reduce risk from severe accidents. (author). 4 refs, 9 figs, 1 tab

[en] The current contributions from the Commission of the European Communities Joint Research Centre to the analysis of severe accidents in LMFBRs are reviewed. The principal tasks are the development of the European accident code 2 (EAC2), an advanced computer code for the analysis of unprotected whole-core accidents based on the existing EAC1, and the performance and analysis of a series of experiments to investigate post-accident heat removal problems exploiting the Faro uranium dioxide melting facility. Other Joint Research Centre contributions in related fields such as the analysis of in-pile subassembly accident and post-accident heat removal experiments are not reviewed. The status of EAC1 is discussed briefly with examples, and then the developments in course designed to lead to EAC2 are described. Models under development include a pin performance and failure model taking account of in-pin fuel motion, a post-failure material motion model and a fast-running three-dimensional transport neutronics package based on the nodal approach. In the Faro facility it is possible to melt up over 100 kg of uranium dioxide by Joule heating and deliver it to a desired test section. The various types of experiments planned are described and indications are given of the results of the first Blokker I tests in which a jet of uranium dioxide obliquely impacts a preheated steel plate. Computational tools have been developed for the analysis of the furnace itself and for the analysis of jet impact tests, fuel penetration experiments and the interaction of a stream of fuel with a sodium pool. The main assumptions of the models are presented together with some indicative results. (author). 10 refs, 7 figs, 1 tab

[en] Poster presentation. 2 refs, 2 figs

[en] The principles of control for the PWR units of Electricite de France have been defined in the case of the first units of the 900 MW level since 1973. Since then, although these general principles have been maintained, a steady evolution in control has taken place; on the one hand, operating experience and safety analyses have given rise to new requirements, such as the safety panel, on the other, on the occasion of the passage to the 1300 MW level, the adoption of programmable automatic control devices to replace electromagnetic circuitry for almost the whole of the system, represented an improved technological development. However, it became apparent that the present structure, in which considerable room was left for information and control by the operator, presented certain limitations. For the new N4 level of 1400 MW, the first unit of which is that of Chooz B in the Ardennes (anticipated entry into service in 1991), it was decided, as early as 1981, to initiate a study involving the organization of the control room and the man-machine interface; this project has now materialized in the form of a control room with data-processing. The study of incidents which have taken place at nuclear power plants, and especially that at Three Mile Island, has shown the need for improving control in accident situations and for employing means of reducing human error, in particular, by ensuring a redundancy of diagnostic information and by enabling operators to understand what is happening and to take correct action in all circumstances: this is the purpose of the safety panel installed in the 900 MW units. (author). 3 figs