MULTIMETAL

Structural performance of multi-metal component

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 Obiettivo del progetto (Objective)

'In a nuclear power plant, a single metallic component may be fabricated from different materials. For example, RPV components are made from ferritic steel, whereas some of the connecting pipelines are fabricated from austenitic stainless steel. As a consequence different components often need to be connected by so-called dissimilar metal welds (DMW). Despite extensive research in Euratom Framework projects such as BIMET and ADIMEW, further work is needed to quantify the structural performance of ageing DMWs.

The first purpose of this project shall be to gather relevant information from field experience: typical locations of DMWs in Western as well as Eastern LWRs will be identified and their characteristics considered, as well as applicable assessment methods. Micro-mechanical modelling of ductile failure processes will be used as an innovative technique to augment current numerical methods for structural integrity assessment of DMWs. The modelling will take account of ageing related phenomena and realistic stress distributions in the weld area and be supported by a comprehensive material test program. A procedure for measuring fracture toughness in DMWs will be developed. The work will also include an assessment of Leak Before Break (LBB) behaviour.

Overall the project will serve to promote common understanding of structural integrity assessment of DMWs in existing and future NPPs of EU member states. This will be the technical basis towards the development of harmonised European codes and standards for multi-metal components, which is currently not available.'

Introduzione (Teaser)

Nuclear power plants employ lots of metal structures often from dissimilar metals that must be welded together. Scientists are developing the basis for currently non-existent standardised tests of these welds to minimise overly conservative and costly inspection.

Descrizione progetto (Article)

The reactor pressure vessel containing the reactor core and coolant is typically made of a different type of steel than some of the connecting pipes. Obviously, the performance of these dissimilar metal welds is of paramount importance to the safety of nuclear power plants. A lack of standardised tests for these welds combined with their critical importance makes extremely conservative decisions necessary regarding their structural condition.

In response to the need for standardisation of integrity and leak-before-break (LBB) assessments, scientists initiated the EU-funded project 'Structural performance of multi-metal component' (http://projects.tecnatom.es/webaccess/multimetal/ (MULTIMETAL)).

Scientists collected field data and experience from typical dissimilar metal welds in western European and eastern European light water reactors. They characterised their physical and metallurgical properties and behaviours, leading to the design of two dissimilar metal weld test configurations. A third weld test configuration is being prepared to benchmark fracture resistance.

The intact mock-ups have been carefully characterised using microstructural studies, hardness measurements and tensile tests, and various fracture mock-ups are being prepared for characterisation as well. In parallel with the comprehensive materials testing programme, the team is developing numerical analyses using innovative micromechanical modelling approaches for ductile failure processes. The combination of experimental data collection and model development will enable scientists to develop standardised procedures.

MULTIMETAL's ultimate goal is to deliver recommendations for measuring the fracture toughness of dissimilar metal welds and for assessing LBB behaviour. Through provision of the technical basis for harmonised European standards for multi-metal components, MULTIMETAL will fill a gaping hole and make a major contribution to the future of nuclear energy in the EU.