F. H. E. de Haan - de Wilde’s research while affiliated with NRG, Nuclear Research & consultancy Group and other places

For many nuclear power plants worldwide the operation period will be extended to 60 or 80 years in the coming years. As the operation period increases, the importance of knowledge of ageing mechanisms increases. In the framework of LTO there is limited knowledge about ageing and structural integrity of concrete structures. Knowledge about the strength of concrete structures and modelling thereof can be improved for a more complete knowledge base on ageing and degradation mechanism in nuclear facilities. Therefore, effort is required to improve the knowledge of concrete, material models and finite element modelling techniques as well as the assessment method. Recent developments have shown that ageing of civil structures receive more attention internationally (E.g. concrete degradation in bunker building Doel). Traditionally a large part of the research and development is focused on mechanical issues like piping and vessels. In order to increase the knowledge in the field of civil structures, the focus is on investigation of ageing of concrete and determining analysis methods. This paper focuses on the development of a practical assessment method for ageing of civil structures. As a first step information from international publications and other sources on civil structures ageing issues and management thereof, will be gathered. Well known international standards taking care of ageing phenomena based on problem areas and good practices are IGALL and GALL. IGALL and GALL contain information tables based on international experience. This is the starting point of the research in finding an assessment methodology for civil ageing management. It will be shown that IGALL and GALL contain very similar elements. Sorting on the AMPs results in a practical set of datasheets with summarizing information per AMP, including the underlying international experience. The datasheets are of limited size, presenting an helpful overview of the relevant structures or components, materials, environment and mechanisms. A method for civil ageing management is proposed which will be applied and developed in more detail in future research. Further research is necessary to develop a specific assessment methodology for concrete.

The reactor vessel of the High Flux Reactor (HFR) in Petten has been fabricated from Al 5154-O alloy grade with a maximum Mg content of 3.5 wt. %. The vessel experiences large amount of neutron fluences (notably at hot spot), of the order of 1027 n/m2, during its operational life. Substantial damage to the material’s microstructure and mechanical properties can occur at these high fluence conditions. To this end, a dedicated surveillance program: SURP (SURveillance Program) is executed to understand, predict and measure the influence of neutron radiation damage on the mechanical properties of the vessel material. In the SURP program, test specimens fabricated from representative HFR vessel material are continuously irradiated in two specially designed experimental rigs. A number of surveillance specimens are periodically extracted and tested to evaluate the changes in fracture toughness properties of the vessel as function neutron fluence. The surveillance testing results of test campaigns performed until 2015 were published previously in [1, 2]. The current paper presents fracture toughness and SEM results from the recent surveillance campaign performed in 2017. The fracture toughness specimen tested in this campaign received a thermal neutron fluence of 13.56 x1026 n/m2, which is ∼8.9 × 1025 n/m2 more than the thermal fluence received by the specimen tested in SURP 2015 campaign. These results from this campaign have shown no change in the fracture toughness from the values measured in the previous SURP campaign. The SEM observations are performed to study the fracture surface, to measure (by WDS) the transmutation Si formed near crack tip and to investigate various inclusions in the microstructure. SEM fracture surface investigation revealed a tortuous (bumpy) fracture surface constituting micro-scale dimples over majority of the fracture area. Islands of cleavage facets and secondary cracks have been observed as well. EDS analysis of various inclusions in the microstructure revealed presence of Fe rich inclusions and Mg-Si rich precipitates. Additionally, inclusions rich in Al-Mg-Cr-Ti were identified. Finally, changes in mechanical properties of Al 5154-O alloy with an increase in neutron fluence (or transmutation Si) are discussed in correlation with SEM microstructure and fracture morphology observed in SEM. TEM investigation of precipitate microstructure is ongoing and those results will be published in future.

The HFR is one of the most powerful and versatile Research Reactors in the world. Because of its strategical importance in the medical isotopes production, after 57 years of operating experience a Continued Safe Operations (CSO) mission will take place. The CSO project structure is based on the outline given in the IAEA draft Safety Guide SSG-48. The ageing management for the HFR is evaluated based on the IAEA Specific Safety Guide SSG-10. Moreover, the approach to the contents of the project is supported by the IAEA Draft Guidelines for Peer Review of “Ageing Management of Research Reactors for Continued Safe Operations”. The HFR is the second Research Reactor (RR) in the world to undergo this type of assessment and its experience will be extremely valuable in setting the international standards for CSO of research reactors. This paper describes the phases of the CSO project, the challenges encountered and the experience built during its development.

For many nuclear power plants worldwide the operation period will be extended from 40 to 60 years in the coming years. As the operation period increases the importance of knowledge of ageing mechanisms like fatigue increases. Knowledge of the influence of the environment is crucial, since environmental fatigue is a relatively new development which is a modification to the existing assessment method and has to be projected to 60 years as well. This paper is a follow up of the ASME PVP2013-97695 paper: overview of international implementation of environmental fatigue. A quantitative comparison of the resulting cumulative usage factors including environmental fatigue is made for the most commonly used and well defined methods. The comparison of the environmental fatigue codes is made on a spray nozzle of the pressurizer. This is a known fatigue relevant location with high stresses due to thermal loading. The high thermal loading is due to the spraying of relative cold water into the warm pressurizer. The comparison is made for 11 methods, sets of fatigue curves and environmental fatigue correction factors (Fen factor), and 4 types of material. The 4 materials are: low alloy, carbon, nickel alloy and austenitic stainless steel. The fatigue curves of ASME 2007, ASME 2010, KTA 1996, KTA 2013, NUREG/CR-6909 and Code Case N-792 are compared. The Fen factors are compared for the following methods: NUREG/CR-6583, NUREG/CR-5704, NUREG/CR-6909, Code Case N-792, JNES SS-0503, JNES SS-1005 and NUREG/CR-6909 rev1. Code Case N-761 is included for the final comparison of the cumulative usage factors including environmental fatigue. The differences in percentages are considerable between the different methods. For this specific case, the difference in cumulative usage factor including environmental fatigue for austenitic steels is 70 %. For nickel alloy materials the difference is 115%. For low alloy materials the difference is the highest: 267%. For carbon steels the difference in cumulative usage factor is 146%. The most conservative cumulative usage factors including environmental fatigue are ASME 2007 or KTA 1996 fatigue curves combined with the NUREG/CR-5704 (austenitic steel and nickel alloy) or NUREG/CR-6583 (low alloy and carbon steel). The next highest results are found by the Japanese methods (JNES-SS-0503 and JNES-SS-1005). The common factor for these methods, is the fatigue curve for austenitic steels as used before 2010. The lowest cumulative usage factors are obtained by implementing NUREG/CR-6909. Using the latest revision of NUREG/CR-6909 the cumulative usage factors increase slightly (about 7%). The paper shows the considerable differences of usage factors when different codes are applied to the same problem. Copyright © 2015 by ASME Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal

For many nuclear power plants worldwide the operation period will be extended from 40 to 60 years in the coming years. As the operation period increases the importance of knowledge of ageing mechanisms like fatigue increases. Knowlegde of the influence of the environment is crucial, since environmental fatigue is a relatively new development which is a modification to the existing assessment method and has to be projected to 60 years as well. This paper contains the results of a literature survey of environmentally assisted fatigue in nuclear power plants. It describes the current status and developments in the world. The main regulatory rules, guidelines and methods from the US, Germany, Japan, Finland and France are presented. At this moment different approaches for incorporating the effect of the coolant water environment exist, although the general trend is towards a more uniform approach worldwide. The most common approach is the incorporation of an environmental fatigue correction factor (Fen) in the fatigue derivation of the cumulative usage factor. The Fen formulas and the S-N fatigue curves differ but the general equations are: Display Formula Fen = N air / N water and Display Formula CUF = Σ U partial * Fen partial Alternatives like using fatigue curves including the environmental effects, using threshold criteria and calculation of an allowable Fen based on testing, are described. Research and material tests are still on-going and subject of international development. An overview of the current international state-of-the-art is presented. Copyright © 2013 by ASME Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal