[en] The reactor study is well underway seen from a broad spectrum of disciplines and technology. The objective power output with a high efficiency direct cycle power conversion unit remains promising after compiling the first critical analysis of the core and the power conversion unit. The stability and controllability of the system are demonstrated by the engineering simulator. The main system and components are basically specified for costing purposes. A first plant layout has been completed demonstrating the positions of main components, personnel movement, installation methods for large components, etc. A cryptic report style presentation includes study objectives, indicating guiding documents, giving an overview of design and analyses work done as well as a few sketches and diagram are included in this paper. Most of these sketches and diagrams are small replicas of large drawings and are therefore not readable but can be used as references. (author)

[en] The system parameters chosen to optimise the thermal efficiency of the Eskom PBMR whilst maintaining component simplicity is discussed. Power Conversion Unit components, which are now at a preliminary design stage comprise a precooler, two turbo units consisting of a turbine driven compressor, recuperator and a power turbine, driving an alternator. Design aspects of every component is mentioned and the inventory method of poorer control is explained with reference to start-up and and shut-down events, the system an effective load following device, down to 4% of full power. Application of the same design principles for HTGRs smaller than 25 MWe is discussed. (author)

[en] Cooling of the Pebble Bed Nuclear Reactor under evaluation in South Africa is primarily effected by the flow of helium through the cavity which contains the nuclear fuel. However, apart from this, a certain amount of heat flows from the reactor cavity, through the graphite barrel and reactor vessel to the containment building and ultimately to the environment During normal operation this passive heat loss represents approximately 1MW for a 100MW reactor and constitutes an undesirable loss of power. In the event of a shutdown or loss of main coolant, however, this passive heat removal is relied upon to remove the decay heat from the core. A study was initiated to simulate the process of this heat removal to provide an indication of the maximum vessel temperature and power transfers after shutdown. However, there is a lack of precise data indicating values for thermal conductivity, heat transfer coefficients, heat capacities or even densities. This paper describes the assumptions made and the manner in which these data were estimated so as to provide what is hoped to be a reasonably accurate estimate of the behaviour of the passive heat removal process. (author)

No abstract available

[en] The abstracts of reports submitted to the Conference include: - New developments of the safe nuclear installations; - NPP ecological safety; - Methods of personnel and population protection; - Waste management safety (at transportation, processing and storage); - Spent nuclear fuel management; - NPP life extension and decommissioning; - Public opinion as an element of NPP safety; - Training of personnel, scientific support and safety culture; - Forecasting of nuclear power and industry safe development; - Development of international cooperation in nuclear power

[en] Retrospective contamination data in Hungary are presented after the Chernobylsk reactor accident in 1986. ¹³⁷Cs concentration data in the atmosphere of the Paks Nuclear Power Plant, Hungary are given from 1986 through 1989. Some other environmental data are shown for other parts of the country. (R.P.) 2 figs

[en] Details of the construction of the Chernobyl sarcophagus are given. Eighteen possible versions of the sarcophagus were examined. The principal idea behind the design that was eventually selected was that both intact and damaged structures of the unit should be used as supports beneath the new cover. A number of special techniques were developed for the work, including technical and organisational measures. (U.K.)

[en] The survey on the oxygen graphite reaction principally describes measurements taken with respect to the kinetics of corrosion of graphite pebbles by air and the formation of aerosols under extreme HTR accident conditions. Measurements were taken in the temperature range between 600 and 1200deg C. The reaction rate in depending on temperature burn off, oxygen partial-pressure and flow rate at pebble beds was investigated. An equation for calculating the reaction rate as a function of these parameters was derived from the measured data. One of the relevant insights gained is the correlation of the reaction rate with the flow rate at high temperatures. It follows that corrosion profiles can only be calculated if all parameters are taken into account. The process of aerosol formation during the corrosion and the interaction of the reactive gas mixture with the suspended particles were examined also in extensive parameter studies. (orig.)

[en] This report compiles environemental radioactivity data based on information provided by member European Community states. The report is organized into six chapters: Airborne Particulates, Deposition, River Water, Drinking Water, Milk, and Chernobyl. Data are reported as national averages; the exception is data for the large nations - Germany, France, Italy, and the United Kingdom - which are reported as three or four regional values for each country. For example, Germany is partitioned into North, Central, South, and West Berlin. Each of the media chapters consists of a discussion/introduction that provides general information on the medium in question and the occurrence of natural radionuclides therein with a short description of sample preparation and measuring methods. Each chapter contains maps showing the location of samples for each country or portion of a country. The majority of the report consists of tabulations by country, year, and quarter of the nuclides and media sampled. Radioactivity reported for each of the sampled media are listed in a table. The chapter on Chernobyl is organized differently. For air particulate concentrations of ¹³¹I and ¹³⁷Cs, air concentration profiles through time are given for 13 different locations. A series of six maps illustrates the spread of ¹³⁷Cs during the Chernobyl event; for up to 60 European locations average daily concecentrations of ¹³⁷Cs in air are plotted for each 24-hour period between 9:00 a.m. on April 29 and 9:00 a.m. on May 5, 1986. In addition, total ¹³⁷Cs deposition by country is tabulated. Several useful appendices to the report include Methods of Calculating Time and Geographical Averages (Appendix A), Addresses of Competent National Authorities (Appendix B) and a bibliography (Appendix C). Despite some errors, this report may be useful to those with interest in environmental transport or modeling

[en] The paper describes the approach taken to establish the maintenance policy for safety-related systems to comply with pre-determined reliability criteria. The design safety guidelines for the Advanced Gas Cooled Reactors require the system unreliability not to be higher than 10E-3 for credible initiating events. For the maintenance tasks, the procedures are developed within a ''Maintenance Inspection and Test Schedule'' document. (author). 4 refs