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Garching bei Munchen, Germany

Zhang C.-L.,GRS Society for plants and Reactor Safety
Journal of Rock Mechanics and Geotechnical Engineering | Year: 2013

The sealing behavior of fractures in clay rocks for deep disposal of radioactive waste has been comprehensively investigated at the GRS laboratory. Various sealing experiments were performed on strongly cracked samples of different sizes from the Callovo-Oxfordian argillite and the Opalinus clay under relevant repository conditions. The fractured samples were compacted and flowed through with gas or synthetic pore-water under confining stresses up to 18MPa and elevated temperatures from 20°C to 90°C. Sealing of fractures was quantified by measurements of their closure and permeability. Under the applied thermo-hydro-mechanical (THM) conditions, significant fracture closure and permeability decrease to very low levels of 10-19 to 10-21m2 were observed within time periods of months to years. The properties of the resealed claystones are comparable with those of the intact rock mass. All test results suggest high sealing potentials of the studied claystones. © 2013 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Source

Merk B.,Helmholtz Center Dresden | Weiss F.-P.,GRS Society for plants and Reactor Safety
Annals of Nuclear Energy | Year: 2011

Different arrangements for the development of a fuel element design with reduced sodium void achieved by the use of the moderating material ZrH are investigated. In the study, the sodium void effect and the major feedback coefficients are analyzed. Besides the feedback coefficients, the influence on the operational parameters like neutron flux distribution, power distribution, and burnup distribution is investigated for the different possibilities of arranging the moderating material in the fuel element. Additionally, the fuel cycle parameters - breeding and minor actinide production - are analyzed. For a first evaluation of the behavior during transients, the influence of temperature changes in the ZrH is studied. © 2011 Elsevier Ltd. All rights reserved. Source

Zhang C.-L.,GRS Society for plants and Reactor Safety
Journal of Rock Mechanics and Geotechnical Engineering | Year: 2016

Characterisation and understanding of the stress-strain-permeability behaviour of a clay host rock during damage and recompaction are essential for prediction of excavation damaged zone and for assessment of its impact on the repository safety. This important issue has been experimentally studied in triaxial compression tests on the Callovo-Oxfordian clay rock in this study. The samples were sequentially loaded by (1) hydrostatic precompaction to close up sampling-induced microcracks, (2) applying deviatoric stresses to determine damage and permeability changes, and (3) recompression along different loading paths to examine reversibility of the damage. The critical stress conditions at the onset of dilatancy, permeability percolation, failure strength, and residual strength are determined. An empirical model is established for fracturing-induced permeability by considering the effects of connectivity and conductivity of microcracks. The cubic law is validated for the variation of permeability of connected fractures with closure. The experiments and results are also presented and discussed. © 2016 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Source

Preischl W.,GRS Society for plants and Reactor Safety | Hellmich M.,Federal office for Radiation Protection
Reliability Engineering and System Safety | Year: 2013

We report about a project aimed to collect human reliability data from the operational experience of German nuclear power plants. Its objective is the validation and extension of existing human reliability databases (in particular, the THERP database). A method utilizing the German licensee event report system to gather the data is described. For certain tasks with specific attributes this method allows to determine the number of times the task was performed in the past, as well as the number of errors that occurred. A statistical method to estimate the corresponding human error probability (HEP) based on these numbers is provided. We have applied this method to the reportable events stored in the database collecting the reportable events in German nuclear installations. In this way up to now 37 HEPs for a wide variety of tasks were obtained, together with information about relevant performance shaping factors. We discuss these HEP estimates and compare them to the THERP database if it provides a HEP for the task in question. In all except three cases we find an agreement within the uncertainty bounds. Moreover, we contribute 21 HEP estimates for which the THERP handbook provides no data, so they serve to extend the THERP database, among them a number of memory related errors. Therefore, this data may serve as an input for the discussion of second generation HRA methods. © 2012 Elsevier Ltd. All rights reserved. Source

Bracke G.,GRS Society for plants and Reactor Safety
Turkish Journal of Earth Sciences | Year: 2012

Safe disposal of radioactive waste is required in all countries using nuclear power, radioactive materials in medicine and in industry or research. This contribution presents an overview of the strategy of final disposal of radioactive waste and summarizes the procedure and present status in Germany. It is concluded that the safe disposal of radioactive waste is feasible but that the public demand for safety has to be met by applying a stepwise, transparent, and traceable development procedure for a repository in a safety case to obtain regulatory and public approval. Source

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