TY - CONF A1 - Grelle, Tobias A1 - Wolff, Dietmar A1 - Probst, Ulrich A1 - Jaunich, Matthias A1 - Völzke, Holger T1 - Material investigation and long-term sealing behavior of Helicoflex® metal seals used in containers for spent nuclear fuel N2 - In Germany spent nuclear fuel is stored and transported in casks that possess bolted lid systems equipped with double jacket metal seals of Helicoflex® type in order to enable safe enclosure. A dry interim storage period of 40 years was planned and the casks are licensed for that time. However, due to political reasons and delayed disposal projects this time period is expected to increase significantly. It is therefore necessary to evaluate the long-term sealing behavior of the casks exceeding 40 years of operating time. In this paper, we discuss our approach to investigate the aging behavior of such metal seals, and to predict the long term sealing behavior. Accelerated aging component tests with seals are performed at temperatures up to 150°C to investigate the course of seal force, useable resilience and leakage rate. Even though these tests have already shown a significant decrease in seal force and useable resilience after aging times of less than 1 year, for most seals the leakage rate stayed better than the specified value. However, observation of the leakage rate has to be continued to determine the effect of the influenced seal properties. As a main influence on the seal long-term behavior the increasing permanent deformation of the outer jacket has been recognized. It is made of aluminum or silver which means that the temperatures that are relevant for the aforementioned application in casks lead to creep deformation. For further investigation of seal behavior a comprehensive research program concerning the material characteristics and aging behavior of the individual seal components, with an emphasis on the outer jacket material, has been launched. The aim is to get a better understanding of the time and temperature dependent creep mechanisms and deformation. The examinations are separated into tests on seal segments and tests on standardized specimen. In order to be able to study the aging process, seal segments are compressed in flanges and stored at temperatures ranging from room temperature to 150°C. After defined time intervals the segments are analyzed by using standardized tests including structure investigation and creep tests. The results are compared with the behavior of the basic raw material for the specimen. This is done to ensure the comparability of the thin jacket material and additional material used for standardized tests. Thus, the prediction of component changes after different ageing times at different temperatures can be made. As a result forecasts on the long term seal behavior are intended. T2 - Waste Management Symposia CY - Phoenix, AZ, USA DA - 05.03.2017 KW - Metal seal KW - Creep KW - Long-term behavior PY - 2017 AN - OPUS4-39891 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Grelle, Tobias A1 - Wolff, Dietmar A1 - Probst, Ulrich A1 - Jaunich, Matthias A1 - Völzke, Holger T1 - Investigation program for evaluation and prediction of the long-term behaviour of Helicoflex® metal seals N2 - In Germany, for the transport and storage of spent nuclear fuel, casks with double closure lid systems are used, which are equipped with Helicoflex® metal seals. The original interim storage period for these casks was planned to be 40 years. However, recent developments indicate that a storage time of more than 80 years might be necessary. Therefore, the current licensing has to be renewed, which requires extended knowledge of the long-term behaviour of all cask components. At the Bundesanstalt für Materialforschung und -prüfung (BAM), metal seals have been aged at temperatures of up to 150 °C for up to 7 years. At regular intervals the seals have been tested for leakage rate as well as their mechanical properties. From these tests pronounced influence of ageing could be shown which results in the decrease of the seal force and the useable resilience. The main reason attributed to these performance changes is the increasing permanent deformation of the outer seal component due to creep. So far, an explicit analytical description of the long-term behavior that could be used for predictions exceeding the tested ageing times was not suitable. In addition to the component tests that were already conducted, a comprehensive research program has been started. The aim is to gain information applicable for the prediction of the seal behaviour for an extended period of time under a certain temperature regime. The individual seal components are tested regarding different material characteristics including creep, deformation and microstructural properties. The comparability of the material characterization is ensured by comparing the basic raw material of the specimen with the actual component material. Furthermore, detailed examinations of the time and temperature dependent deformation behaviour are realized by ageing seal segments at multiple temperatures for different periods of time and employing standardized tests. By analyzing the newly acquired data in combination with the long-term component tests analytical forecasts of the long-term behavior of the seals are intended. T2 - Annual Meeting on Nuclear Technology (AMNT) CY - Berlin, Germany DA - 16.05.2017 KW - Metal seal KW - Creep KW - Long-term behavior PY - 2017 AN - OPUS4-40956 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -