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Plant Life Management (PLiM)
for Safe Long Term Operation (LTO)

Development of Technical Guidelines

Nuclear Energy Series (NES) on Methods for the Replacement of Heavy Component Replacement (steam generator, reactor vessel head and reactor internals)

The replacement of heavy components is the result of widespread stress corrosion of Inconel 600 (and alloys 82/182) in the primary system. Following the corrosion of steam generator tubes, which led to the first steam generator replacement (SGR) operations, work has begun on reactor vessel head replacements (RVHR) and pressurizer replacements, pending treatment of the dissimilar butt welds (DBW).

Operators are looking for ways to optimize plant lifetime, and must therefore prevent stress corrosion in primary components, while combating other phenomena, such as thermal fatigue or certain metallurgical weaknesses.

Utilities are looking for ways to optimize plant lifetime, and must therefore prevent stress corrosion in primary components, while combating other phenomena, such as thermal fatigue or certain metallurgical weaknesses. Since the early 2000&s, the driving factors for main component replacements are more complex and interconnected. In respect of the regulatory safety issues, Operators have developed economic models that help them make their decision on main components replacements and fix the optimum dates.

Component replacement is often the most feasible solution to solve the problems associated with primary water stress corrosion cracking (PWSCC) of Alloy 600. Even if mitigation and /or repair were a local solution, replacement offers many advantages when addressing the assortment of potential susceptible parts contained in a major component. The replacement of heavy components is the result of widespread stress corrosion of Alloy 600 (and alloys 82/182) in the primary system. Following the corrosion of steam generator tubes, which led to the first steam generator replacement (SGR) projects, work has begun on reactor vessel head replacements (RVHR) and pressurizer replacements.

The NE Series document is dedicated on Heavy Components Replacement considered strategic for plants life management and not included in current maintenance replacement carried out by utilities. The major and heavy components to be considered are:

• Steam Generators for PWR and WWER plants;
• Reactor Vessel Head for PWR plants;
• Reactor Internal Components for BWR plants;
• Reactor Vessel Internals for PWR plants;
• Pressurizer for PWR plants;
• Reactor coolant piping/ recirculation piping PWR and BWR plants.

The document will be published this year.

References:

• IAEA-TECDOC-1557, Assessment and Management of Ageing of Major Nuclear Power Plant Components Important to Safety: PWR Vessel Internals, Vienna (2007)
• IAEA-TRS-448, IAEA, Plant Life Management for Long Term Operation of Light Water Reactors, Vienna (2006)
• IAEA-TECDOC-1471, Assessment and Management of Ageing of Major Nuclear Power Plant Components Important to Safety: BWR Pressure Vessel Internals, Vienna (2005)