Community Research and Development Information Service - CORDIS


General Review of Dissimilar Metal Welds in Piping Systems of Pressurised Water Reactors, Including WWER Designs

Funded under: FP6-JRC


Dissimilar metal welds (DMWs) are commonly found in the primary piping of pressurized water reactors, including the so-called Russian design water moderated, water cooled energy reactor (WWER). The most important DMWs in safety critical locations, i.e. those that cannot be isolated from the reactor coolant system, are those between the austenitic main coolant line piping and ferritic nozzles on the reactor pressure vessel and the steam generators, as well as that between the pressurizer and austenitic surge line. Hence overall there is a large number of DMWs in operation. Their type depends on the specific reactor design, the materials used and the welding procedure. The principal design and fabrication of PWR and WWER dissimilar metal welds are nonetheless comparable, involving ferritic and stainless steel base materials, with various weld filler and buttering alloys. For PWRs the buttering is either a stainless steel or a Ni-base alloy; in the case of WWER plants it is a stainless steel alloy with an intermediate Ni-content.
DMWs are generally designed and fabricated to high quality standards. However some instances of flaws and/or leakages in operation have been reported. Potential damage is difficult to detect with inservice inspection systems because of variations in grain size, the dendritic nature of the weld microstructure, variations in sound velocity, repairs and geometric factors such as weld shape, component form and accessibility. Investigations of potential degradation mechanisms, integrity assessment methods and leak-before-break concepts have been performed in national projects and under EC supported programmes such as TACIS-PHARE, as well as the R&D Framework Programme (BIMET, ADIMEW and NESC).
This review illustrates that many factors are generic to the different plant designs and that therefore there is considerable potential for exchange of best practices and for harmonisation.

Additional information

Authors: MITEVA R, Bulgarian Nuclear Regulatory Agency, Sofia (BG);TAYLOR N G, European Commission, Joint Research Centre, Institute for Energy, Petten (NL)
Bibliographic Reference: EUR 22469 EN (2006), 60 pp. Free of charge
Availability: Available from European Commission, JRC Knowledge Management Unit, Ispra (IT) Tel: +39 033278 9893 Fax: +39 033278 5409 E-mail: or Bruxelles (BE) Tel: +32 2 295 76 24 Fax: +32 2 299 63 22
Record Number: 200718934 / Last updated on: 2007-03-16
Original language: en
Available languages: en