[en] The wet storage facility ISF-1 is needed for temporary interim storage of the spent fuel assemblies on site in the frame of the decommissioning activities of Chernobyl NPP. Since the remaining fuel assemblies have to be unloaded from the reactor units under decommission, and the construction of the planned long term dry storage on site has been delayed due to technical and other problems, the ISF-1 will for a certain time period be the only available storage facility on site and has to be operated at its full storage capacity. In the present paper the work of western European Technical Support Organizations (TSOs) in order to support licensing authorities of eastern European countries and to ensure further implementation of international accepted safety standards is explained at the example of the performed review of the safety assessment report (SAR) of the wet interim nuclear spent fuel storage facility SFSF-1 at the Chernobyl NPP site. The slides of the presentation have been added at the end of this paper. (authors)

[en] Results of a 3 years study regarding the changes of MX-80 bentonite after reaction with solutions of different ionic strength and pH, occurring in repositories in granite, in clay and in salt formations are presented. Each solution reacted differently with the bentonite and affected differently the resulting mineralogy and swelling pressure (SWP). SWP were highest in contact with water (over 4 MPa), significantly lower in contact with low ionic strength solutions (around 2 MPa) and lowest in contact with high saline brines (mostly under 1 MPa). Alteration and partial dissolution of montmorillonite was observed. The Mg, Al and Si contents in the solutions increased with reaction time. Concomitantly in the octahedral layers of montmorillonite Mg was substituted by Al and the interlayer charge decreased. The correlation between the alteration process, the charge reduction and SWP is presented. The key for the observed mineralogical alteration may be the acidity of water in the interlayer space. This may explain why the alteration in compacted bentonite is faster than in the non compacted. All results can be explained by processes which lead to a pyrophyllitization/kaolinitization and Si-excess of the montmorillonite particles. These processes may lead in the long run to a significant or even total loss of swelling capacity of compacted bentonite, if high saline solutions and cement are involved. The slides of the presentation have been added at the end of the paper. (authors)

[en] An enhanced method for the assessment of cable failures caused by fire has been developed by GRS based on a failure mode and effect analysis (FMEA). It intends to overcome the limitations of simplified screening methodologies. The FMEA tool uses a database that contains all the relevant information on cables of the reference NPP and information on components (description, type, operational mode, etc..)

[en] As the subsidiary of the Belgian Federal Agency for Nuclear Control (FANC), Bel V performs the regulatory inspections and safety assessments in nuclear installations, according to the Belgian Royal Decree of July 20. 2001. This Royal Decree is not meant to give a recipe on how to perform inspections and therefore requires interpretation. This paper presents the inspection techniques and practices applied by the Bel V inspectors in order to comply with the spirit of the Royal Decree, using the available resources. AT Bel V the inspections are based on the sampling principle in combination with the experience feedback process. Inspections occur frequently, typically once a week. Concerning documentation, the inspector looks at a sample of documents, the licensee knows he has to produce high-quality documents that have to be correct and as a consequence the licensee has to set internal independent review. If the inspector were to look at every document, the licensee may consider the inspector as a mere reviewer as he checks every document and the global quality of the documentation may decrease. In order to optimize the inspections, the inspection reports circulate among all the members of Bel V (inspectors and experts). Everyone is invited to comment these reports if he deems that the inspector should be made aware of an important issue, that the inspector should take a closer look at a certain aspect,.... These remarks help the inspector to prepare the next inspection. The slides of the presentation have been added at the end of the paper

[en] For decommissioning of nuclear facilities usually the two decommissioning strategies 'immediate dismantling' or 'deferred dismantling (safe enclosure)' are applied. In general, immediate dismantling is regarded as the more advantageous and more preferable option. Accordingly, immediate dismantling is the mostly selected option. Nevertheless, only in a case by case analysis it can be shown, which decommissioning option is the better one e. g. with respect to technical aspects or to a use of the facility / remaining facility. For two real decommissioning projects of two similar research reactors of TRIGA type GRS with support of the operator, German Cancer Research Center Heidelberg, performed a study on possible advantages of the two different strategies selected. While the first research reactor, TRIGA HD I, was dismantled immediately, the second research reactor, TRIGA HD II, was dismantled after a 20 years period of safe enclosure. As a result, it could be shown, that the selected different decommissioning strategies reflected the special conditions of each both research reactor in best way, so that a clear preference for one of the two decommissioning strategies can not be deduced. The slides of the presentation have been added at the end of the paper. (authors)

[en] Most countries favour compacted air-dry bentonite for engineered barriers in final repositories for nuclear waste. While the hydrophilic properties of bentonite appear to be ideally suited for minimising any contact of water with the waste the process of re-saturation is not fully understood yet. The established codes for modelling the re-saturation of compacted bentonite are based on the assumption that the hydraulic processes can be described as a two-phase flow of liquid water and air. Many models additionally take vapour flow into account. Investigations performed at GRS for some time now suggest, though, that compacted bentonite coming into contact with liquid water will not re-saturate via the liquid water phase but mainly by evaporation in the pore space and subsequently by vapour diffusion. The present paper describes some of the basics of the established thermo-hydro-mechanically (THM) coupled codes in order to point out discrepancies with microstructural phenomena in a re-saturating bentonite. The alternative conceptual model being more closely based on the microstructural effects avoids these inconsistencies. It is subsequently described in detail as well as the procedure to validate the model. The paper also summarises the history of the alternative model. The slides of the presentation have been added at the end of the paper. (authors)

[en] The objective of this EURATOM collaborative project is to understand Redox phenomena controlling the long-term release/retention of radionuclides (ReCosy programme) in nuclear waste disposal and to provide tools to apply the results to safety assessment. The project has been organized into 6 task forces: 1) implications of Redox for safety, 2) development of Redox determination methods, 3) Redox response of defined and near-natural systems, 4) Redox reactions of radionuclides, 5) Redox processes in radionuclide transport, and 6) Redox reactions affecting the spent fuel source-term

[en] This series of slides presents, first the 2008 context of nuclear power: a rising demand and a nuclear plant construction set to accelerate after 2010 and secondly, the role that TSOs (Technical Safety Organizations) are expected to play by nuclear industry. This role must be important on 4 issues: the standardized products, the licensing support, the international cooperation and the keeping of competence. The standardization of reactors could allow a one-step licensing that means the merging of the construction license and of the operation license into a unique license, and the mutual acceptance of licenses by TSOs. Concerning the licensing support, TSOs are wished to intervene at the very early stage of design work for new reactor concepts and to cooperate with countries that do not have adequate structure for nuclear licensing. Concerning the international cooperation, TSOs are expected to promote close partnership between national TSOs through a mutual exchange of information, the exchange of experts or common licensing activities. As for the keeping of competence, TSOs must have the adequate staff to work on new reactor concepts

[en] Several years ago, three European TSOs (Technical Safety Organizations) AVN (Belgium), GRS (Germany) and IRSN (France), sharing information and experience for a longer time period took the initiative to develop a common Safety Assessment Guide, with the objective to set down the harmonized principles applied in the three organisations to ensure that, whatever the technical analysis could be, the safety assessments are performed according to the same lines and can therefore be used with the same confidence by the people concerned. Later, this initiative was extended to the development of several technical Safety Assessment Guides and the activity was opened towards all EUROSAFE partners. This paper gives an overview of the programme, its objectives, achievements and future prospects. The slides of the presentations follow the paper. (authors)

[en] The information (IT) security objectives at NPPs are first the traditional ones: confidentiality, integrity and availability but in addition others more specific to nuclear power plants like: -) the absence of feedback or reaction of an IT system related to safety systems and -) IT systems must not contribute or worsen malicious attacks endangering nuclear safety. The implementation of IT security zones means the logical grouping of IT systems based on similar importance for safety or on similar protection requirements. The communication across zone boundaries are strongly regulated by policies and technical decoupling mechanisms (that may ensure strict one-way communication for instance). The communication restrictions between zones rise as the demands of protection levels of zones increase but requirements for inter-connecting IT systems are growing permanently. IT systems are typically not set up as 'IT security ready' by vendors so IT security involved staff with a broad knowledge covering IT, nuclear operations, safety and security. This document is composed of the slides of the presentation