LIFE EXTENSION | FOCUS ON THE US
● ‘Boral degradation’ addresses the potential for spent fuel racks that use Boral for neutron absorption experiencing problems with swelling and degradation of the plates over long periods of time.
Aging management programmes Plant safety and efficiency are managed via a series of aging management programmes (AMPs) focused on specific components or systems. There are four types of aging
maintenance programmes: ● Prevention programmes that stop the effects from occurring
● Mitigation programmes that slow the effects of aging ● Condition monitoring programmes that examine the presence and extent of aging
● Performance monitoring programmes that test the ability of a structure or component to perform its intended function.
In preparing for any licence renewal application, existing programmes and activities that apply to systems, structures, components, or commodity groups are reviewed because they are often based on a regulatory commitment or requirement, rather than specifically designed for aging management. At Comanche Peak the renewal application says that
many of these programmes had the required attributes and adequately manage aging effects. However, the plant operator will introduce several new ageing management
programmes for the purposes of licence renewal. They are: ● Thermal aging embrittlement of cast austenitic stainless steel (CASS). This includes a screening methodology to determine component susceptibility to thermal aging embrittlement based on casting method, molybdenum content and ferrite percentage. For “potentially susceptible” components, thermal aging embrittlement management is accomplished through plant-specific flaw tolerance evaluations. Inspections or evaluations are not required for components that are determined not to be susceptible to thermal aging embrittlement. Three reactor coolant loop components are susceptible to thermal aging embrittlement in Unit 1 – a crossover leg 40-degree elbow, a crossover leg 90-degree elbow,
and a crossover 90-degree elbow with plenum. A plant- specific flaw evaluation using plant-specific geometry and stress information was completed for all three of the components and it was determined that even with thermal aging, the susceptible CASS components are flaw tolerant for 60 years of service.
● PWR vessel internals. The new aging management plan is used to manage the effects of age-related degradation mechanisms that are applicable to reactor vessel internal components. These degradation mechanisms include: cracking due to stress corrosion and fatigue or cyclic loading; loss of material induced by wear; loss of fracture toughness due to thermal aging and neutron irradiation embrittlement; change in dimension due to void swelling or distortion; and loss of preload due to thermal and irradiation-enhanced stress relaxation and creep.
● One-time inspection will verify the system-wide effectiveness of the existing water chemistry, fuel oil chemistry and lubricating oil analysis AMPs. It will inspect a representative sample of components, which is 20% of the population, and if possible it will include components most susceptible to aging, due to their time in-service or the severity of operating conditions at their location.
● Selective leaching requires one-time inspections to demonstrate the absence of selective leaching. As above, it will be applied to a representative sample of susceptible components such as piping, valve bodies, pump casings, heat exchanger components and bolting. The materials of construction for these components that are susceptible to selective leaching are grey cast iron, ductile iron and copper alloy with greater than 15% zinc or 8% aluminium. The inspection of 20% of susceptible components will include visual examinations, supplemented by hardness tests or other mechanical examination techniques such as destructive testing, scraping, or chipping of selected components.
● One-time inspection of small-bore piping and inspection of internal surfaces in miscellaneous piping and ducting components. This AMP will incorporate volumetric inspections of a sample of this Class 1 piping focused on full and partial penetration welds. It will include measures to verify that degradation is not occurring, thereby either confirming that there is no need to U
Above: Comanche Peak 1 and 2 are sited 65 miles (108 km) southwest of Dallas-Fort Worth, Texas
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