Improving Global Quality of Life

Following these codes assures initial high quality construction and appropriate ongoing inspections, with
repairs performed to maintain the structural integrity of the systems necessary to assure a safe shutdown of
the plant once it has started operation.
One can refer to Nuclear Construction Lessons Learned Guidance on best practice: welding – The Royal
Academy - ISBN: 1-903496-82-9.
Contractors that build these facilities mainly employ welders that are skilled in manual techniques using the
GTAW and SMAW processes. Typically, piping butt welds are performed with GTAW for the root pass and
followed by a second pass of GTAW, then the welds are completed using SMAW. This combination is meant
to assure that the higher quality GTAW process is used to seal the inside diameter and the higher production
process SMAW is used to fill the balance of the joint volume. This method has been in use since the early
1970s and is still the predominant method to date. Since 2005, there has been a desire to use new highly
developed GMAW power sources such as Miller Electric’s RMD and Lincoln Electric’s STT to replace the
GTAW/SMAW method. These two methods are starting to be placed into the hands of welders. It should be
noted that many welders do not transition well to this change without adequate training.
Equipment manufacturers’ employ SAW for typical construction. This process is well established with both
high production and high quality benefits. In a factory environment where the vessels can be manipulated,
SAW is a nearly perfect process. SAW can easily be incorporated into an automated production line. When
more portable welding is necessary or for certain smaller production assembly, FCAW is typically employed
with gas shielding.
The various issues relating to welding technology for nuclear power plants must keep pace with the advances
and innovations in welding technology. While materials pose exciting challenges and thus opportunities to
materials scientists, development of welding technology for joining these materials pose further exciting
challenges for technologists, to enable realisation of the objectives of sustainable development of the
nuclear energy option. Development of welding technology for nuclear energy systems involves exploitation
of the full potential of the latest welding processes, and also the harnessing the benefits through developing
of knowledge-based expert systems for failure analysis and suggesting repair and refurbishing strategies and
weld process modeling and control, weld-bead profile analysis for quality control, microstructure prediction
and mechanical property estimation.
Alloys that were used in the first generation of nuclear plants have been improved on since the service
conditions are now better understood. Examples include the use of unstabilised 304 stainless steel in Boiling
Water Reactor Recirculating Coolant Systems and the use of Inconel 600 fillers and base metals in the vessel
nozzles which are both attacked by Inter Granular Stress Corrosion Cracking. Other corrosion mechanisms
and fatigue will be addressed by material improvements using new alloys and by cladding existing alloys
with exotic materials by Explosion Welding. New welding processes and techniques will also be used to
address fatigue damage (chamfered fittings or 2 to 1 profile socket welding) and lower residual stress from
GMAW versus GTAW/SMAW.
In the future, large equipment manufacturers’ will continue to use SAW but high quality Hot Wire GTAW
will find a place in attaching smaller bore nozzles such as the numerous Control Rod Drive Mechanism
housings. The introduction of the new highly automated process will require new equipment which is now
just beginning to be developed. Welding Operators for this specialised fabrication will be in high demand.
Currently the training for such equipment is offered by the equipment suppliers.
Due to the heightened safety requirements of nuclear power all welding will require certification testing of
individuals and full documentation of welding consumables used and recording of the welding procedure
variables that are used. This is carried out by the Welding Engineering professional and/or Quality Control
personnel. Presently the collegiate system is not prepared to train which is attributed to a lack of focused
foresight by national leadership. Costs for teaching welding professionals is considerably higher than other
92 Improving Global Quality of Life Through Optimum Use and Innovation of Welding and Joining Technologies