Discussion on recent concrete containment designs

After a short description of some containment designs of existing power plants in France and Germany this paper addresses, from a civil engineering point of view, current investigations being jointly performed by EDF and SIEMENS within the framework of the basic design for the future European Pressurized Water Reactor (EPR) containment. The prestressed containment will be tested at its design pressure of 6.5 bar(abs) and a design leak rate below 1%2of the containment volume in 24 h, covering a LOCA pressure of 4.2 bar(abs) with 12 h grace period for spraying and a hydrogen deflagration accident. For this project the Safety Authorities require in addition the verification of leak tightness beyond the design pressure of 6.5 bar(abs) in order to mitigate the consequences of all possible severe accidents. Although the design of the prestressed containment is such, that without a liner the containment function will meet leak rate requirements with respect to pressures and temperatures beyond the test conditions, investigations for a composite liner glued onto the inner side of the containment wall are being performed to gain further margins. Based on pre-tests already performed at the SIEMENS laboratories and at the University of Karlsruhe the most promising materials are vinyl esters (VE) or epoxy resins reinforced by glass-fibres, so called glass-fibre-reinforced plastics (GRP). A qualification program considering the specific aspects of nuclear licensing for such materials in France and Germany is under way. Of special interest is their behaviour under high temperatures, irradiation and extensive cracking of the containment wall during postulated severe accident conditions. Intermediate results will be presented. Some information concerning the large scale mock-up being erecting under the leadership of EDF at the site of CIVAUX/France will be given. The aim of these tests is to estimate the ultimate leak rate of a containment wall without a liner for dry air (pressure test) and an air-steam mix (accident) and to test the behaviour of a composite liner up to the failure of the containment wall. (C) 1997 Elsevier Science S.A.