Reactor Metals
Numerous
types of metal alloys can be found throughout the primary and secondary systems
of nuclear power plants. Some of these materials (in particular, the reactor
internals) are exposed to high temperatures, water, and neutron flux, creating
degradation mechanisms in the materials that are unique to reactor service.
Research projects in this area will provide a technical foundation to establish
the ability of those metals to support extended operations.
Concrete
Large areas of most nuclear power plants have
been constructed using concrete and there are some data on performance through
the first 40 years of service. In general, the performance of reinforced
concrete structures in nuclear power plants has been very good. Incidents of
degradation initially reported generally occurred early in the life of the
structures and primarily have been attributed to construction/design
deficiencies or improper material selection. Although the vast majority of these
structures will continue to meet their functional or performance requirements
during the current and any future licensing periods, it is reasonable to assume
that there will be isolated examples where as a result primarily of
environmental effects, the structures may not exhibit the desired durability
(e.g., water-intake structures and freezing/thawing damage of containments)
without some form of intervention.
Cabling
Cable aging mechanisms and degradation is an
important area of study. The plant operators carry out periodic cable
inspections using NDE techniques to measure degradation and determine when
replacement is needed. Degradation of these cables is primarily caused by
long-term exposure to high temperatures. Additionally, stretches of cables that
have been buried underground are frequently exposed to groundwater. Wholesale
replacement of cables is likely economically undesirable for plant operation
beyond 60 years.
Mitigation Technologies
Mitigation
technologies include weld repair, post-irradiation annealing, and water
chemistry modifications. Welding is widely used for component repair.
Weld-repair techniques must be resistant to long-term degradation mechanisms.
Extended lifetimes and increased repair frequency welds must be resistant to
corrosion, irradiation, and other forms of degradation. The purpose of this
research area is to develop new welding techniques, weld analysis, and weld
repair. A critical assessment of the most advanced methods and their viability
for LWR repair weld applications is needed. Post-irradiation annealing may be a
means of reducing irradiation-induced hardening in the RPV. Water chemistry
modification is another mitigation technology that warrants
evaluation.