According to the World Nuclear Association, approximately 440 nuclear power reactors are operating, generating about 10% of the world’s electricity. More than 55 power reactors are under construction, 90 have been ordered or planned, and 300 are proposed, mainly in Asia. Because nuclear power has zero carbon emissions and is a reliable domestic energy source, there is a renewed desire to keep existing plants online. However, these plants may need replacement components and other enhancements to ensure safe operation while extending plant life. With the industry poised to see an increase in nuclear welding activity, it is worth revisiting the critical role filler metals play (Figure 1).
For example, in nuclear power plants, steam generators provide a similar function as heat exchangers; however, the stakes are higher. A small defect in fabrication can lead to radiation transfer from irradiated to non-irradiated water. Other welding applications include those on reactor pressure vessels, pressurizer vessels, reactor coolant piping, line valves and safety valves, as well as the nuclear facility’s structural elements and supporting infrastructure.
Quality assurance bodies
Safety is the top priority in the nuclear industry, and the industry must adhere to a strict set of rules and standards for safe operation and quality assurance during the construction and operation of nuclear handling sites. The leading quality assurance bodies include:
- The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) Section III details the quality requirement for components in nuclear power plants.
- The RCC-M, “Regles de Conception et de Construction des Materiels Mecaniques des Ilots Nucleaires PWR” (“Construction Rules for the Mechanical Components of PWR Nuclear Islands”), which gathers within one set of
- all design and construction practices relating to the mechanical components of French pressurised water reactor nuclear islands.
- ISO 3834, which provides welding best practice details for metals and ensures quality adherence for national and international use.
When searching for filler metals, look for a supplier with a Quality System Certificate (QSC) issued by ASME, which verifies a Material Organization’s quality system program. The QSC certificate indicates a quality system in which the company’s operations, processes and services related to the procurement, manufacture and supply of material and source material are performed in accordance with the ASME BPVC, Section III requirements. ASME audits the certificate holder frequently, confirming adherence to ASME codes.
By working with QSC holder, fabricators and contractors performing nuclear welding are assured that their consumables:
- Are produced with the strictest quality control measures,
- Meet codes for nuclear pressure vessels,
- Perform with good weldability and high operator appeal, promoting consistent and high-quality results,
- Provide chemistries that offer excellent mechanical properties and performance in extreme service environments (e.g., high temperatures, resistance to corrosion and brittleness from neutron irradiation).