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LONGLIFE Final Workshop proceedings



TOPIC: Reactor systems, Fission-2009-2.1.2
"Treatment of LONG term irradiation embrittLement
In RPV saFEty assessment"
In view of the increasing age of the European NPPs and envisaged lifetime extensions up to an EOL of 80 years, there is a need for an improved understanding and prediction of RPV irradiation embrittlement effects connected with long term operation (LTO). Irradiation effects caused by high neutron fluences such as the possible formation of Late Blooming Phases and as yet other unknown defects must be considered adequately in safety assessments. However, the surveillance database for long irradiation times (>20 years) and for low neutron flux is sparse. Consequently the treatment of such long term irradiation effects is afflicted with large uncertainties.
In this context the availability of microstructural data is essential for the understanding of the involved mechanisms.
The overall objective of the project is to enhance the knowledge on LTO phenomena relevant for European Light Water Reactors, to assess prediction tools, codes and standards including proposals for improvements, and to elaborate best practice guidelines for RPV irradiation surveillance. In this way, the proposed work will improve the RPV safety assessment of existing European LWRs under long-term operation and for Generation-III reactors under construction, and will support ageing management and plant life extensions.
The proposed scope of work comprises the following tasks:
·              Summary of the boundary conditions for LTO and systematic (re)evaluation of the international prediction procedures of irradiation embrittlement
·              Investigation of specific LTO relevant phenomena like late blooming phases and flux effect. Evaluation of the role of Ni, Mn, Cu, P under the perspective of LTO
·              Generation of microstructural data of irradiated representative or original RPV materials. Demonstration that damage models are (or not) consistent with the mechanisms of irradiation damage in the LTO (use of prediction tools, link to PERFORM60)
·              Comparison and correlation of microstructural data with mechanical properties and identification of the most important influencing factors (link with PERFORM60)
·              Assessment of the influence of high fluences on fracture toughness curves shape
·              Survey of available results of RPV materials from decommissioned plants with the aim to validate surveillance data and to study specific irradiation effects relevant for LTO
A key point of the proposed work, containing different steels originating from European LWRs and some RPV like steels being sensitive for LTO irradiation effects, is the pre-selected table of materials for the planned examinations.
As a final outcome, recommendations for RPV irradiation surveillance under LTO conditions will be elaborated, which will contribute to a reliable monitoring of long-term irradiation effects and support European efforts towards harmonisation of European procedures for RPV surveillance and safety assessment in the light of extended plant lifetime.

September 17 – 21, 2012
University of Seville
Seville, Spain
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