80-Year Ultra-Long Service Life! Design Approach for the Next-Generation Steam Turbines Adapted to SMRs

Among the commercialization indicators for Small Modular Reactors (SMRs), the 80-year design life is a highly iconic requirement. Conventional coal-fired power plant steam turbines are typically designed for a service life of 40 years, while large-scale nuclear power steam turbines are mostly planned for 60 years. SMR projects extend the service cycle to 80 years, meaning the steam turbine must operate stably and continuously under the coupled effects of wet steam erosion, cyclic alternating stress, medium corrosion, and low-dose radiation exposure—posing a disruptive challenge to the entire equipment reliability system.

The 80-year long-life design is not simply a matter of thickening original materials or enlarging structural dimensions. It is a comprehensive reliability management system spanning the entire lifecycle of design, manufacturing, and maintenance. The core pressurized rotating component—the steam turbine rotor—is the top priority in long-life design. Under prolonged wet steam conditions, conventional rotor materials gradually exhibit material embrittlement and fatigue damage accumulation. Rotors adapted for SMRs require special alloy steels with resistance to temper embrittlement and stress corrosion cracking, with strict control of smelting purity and reduction of impurity element content. Meanwhile, forging and heat treatment processes are optimized to homogenize the internal metallurgical structure and slow down material aging.

Blades are another weak link. Under wet steam conditions, water droplet erosion, vibration fatigue, and corrosion combine to continuously consume blade service life. In addition to wet steam protection and surface strengthening processes, long-life design also optimizes blade root connection forms. Fir-tree blade roots with more uniform load distribution are adopted to reduce local stress concentration. At the same time, vibration modes under start-stop and load-variation conditions are finely calibrated to avoid resonance ranges and prevent fatigue accumulation from long-term alternating vibration. Stationary components such as fasteners, gland seals, and diaphragms cannot be overlooked either. Minor creep and corrosion aging, on an 80-year timescale, can potentially develop into hidden hazards affecting unit safety.

Aging monitoring and periodic assessment are essential safeguards for achieving ultra-long service. SMR steam turbines cannot wait until components visibly fail before conducting maintenance; a continuous condition monitoring system must be established. Online monitoring systems collect data in real time on vibration, temperature, clearances, leakage, and rotor stress. Combined with periodic non-destructive testing, flaw detection is performed on high-risk areas such as rotor center bores, blade roots, and weld seams. Aging assessment models are also established to quantitatively calculate damage accumulation rates based on operating hours, start-stop cycles, and wet steam exposure duration, predict remaining component life, and formulate maintenance and replacement plans in advance—transforming passive repair into proactive life management.

The redundancy design at the nuclear safety level complements the long-life objective. Although the turbine island belongs to the conventional island and is isolated from the nuclear island, SMR sites are compact and risks from operating condition fluctuations require fully adequate safeguards. The unit is equipped with multiple independent overspeed protection systems and emergency trip devices, along with redundant lubricating oil and jacking oil systems, to prevent serious accidents caused by the failure of a single aging component. In material selection, radiation effects are also considered. For components adjacent to radioactive steam circuits, materials with low irradiation embrittlement sensitivity are selected to control mechanical property degradation caused by long-term radiation exposure.

Long-life design ultimately serves the full-cycle economics of SMR projects. Extending equipment service life dilutes initial investment costs, reduces the frequency of major overhauls and large-component replacements, and minimizes long-term downtime losses. However, long life also introduces new engineering challenges: many materials and structures lack 80 years of actual operational data, and the industry must rely on accelerated aging tests and simulation to continuously validate design boundaries.

As SMR demonstration projects are implemented, steam turbine long-life reliability technology continues to iterate. The three major directions—material upgrades, refined life-cycle simulation, and online intelligent monitoring—will work in synergy to lay a solid foundation for the safe 80-year operation of conventional island rotating equipment for small modular reactors.