Filler Metals used in the Nuclear Industry
Q : What filler metal grades are selected for nuclear service environments , and what are some of the mechanical and environmental stresses they ’ re subject to ?
Manual TIG welding ( GTAW ).
Meet the columnist
Peter Stones
IEng MWeldI IWE / EWE As part of the ESAB Specialty Alloys Group , Peter is technical support for stainless and nickel alloy filler metals . Peter is actively involved with TWI and is a non-executive director of The Welding Institute . Peter worked for Sandvik for 10 years and was Global Product Manager for Sandvik Welding up to 2018 , when ESAB purchased the filler metals business .
A : Apart from the life of the fuel , the safe and economical operation of any nuclear power system relies on its construction materials remaining sound for up to 60 years . They need to maintain mechanical properties while constantly subject to sources that can cause construction materials to degrade , including high temperatures and pressures in a corrosive environment and bombardment with high energy particles released during fission . The following table summarises the expected environments for two types of nuclear power systems . The pressurised water reactor ( PWR ) is older technology
Reactor Type yet constitutes the majority of the world ’ s plants . With recent decisions to extend the operating life of nuclear facilities , this old design will remain highly relevant for welding operations . Modern sodium-cooled fast reactor systems operate at higher temperatures , pressures and radiation doses . Russia , Japan , India , China , France and the USA are investing in the technology .
Requirements of filler metal grades Welding is considered the most critical operation in constructing a nuclear power plant . Therefore , special attention must be paid to the
Coolant Inlet Temperature
Coolant Outlet Temperature welding procedure and the production and delivery of welding consumables . The requirements of any materials going into a high-risk environment where failure is life-threatening are the same for every application . Nuclear applications have an added risk due to the materials being bombarded with high-energy particles at an atomic level ; consequently , materials behave differently . The filler metals must conform to the required composition specification as defined in the standards . In addition , they must be free from impurities . Typically , the grades are designed to have extremely high resistance to hot cracking
Maximum Dose Pressure Coolant
(° C ) (° C ) ( dpa *) ( Mpa )
Pressurised Water Reactor 290 320 100 16 Water
Sodium Cooled Fast Reactor 370 550 200 0.1 Sodium
* dpa is Displacement Per Atom and is a standard parameter in the determination of radiation damage in materials . For 1 dpa , on average each atom has been knocked out of its lattice site once .
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