Nuclear power plants are the most rigorous and extreme environment for pipes. Carbon steel pipes have been so far used in transportation and distribution of water in nuclear power plants. Corrosion of steel water pipes in the safety-related piping systems of ageing nuclear power plants is becoming a safety concern and a significant operational cost, along with potential future liability. According to the Electric Power Research Institute, the physical maintenance of degraded steel water pipe systems, combined with the operational costs of shutting a plant down during repairs, is already costing some nuclear utilities up to US$25 mln pa. The problem is particularly sensitive when the water pipe systems in question are safety-related, such as the essential service water (ESW) systems that stand ready to cool a reactor when needed. In these systems, water-cooled secondary heat exchangers are used to maintain public safety and power generation continuity. Lost revenue from a system shutdown, which is likely when an ESW system fails, can be more than US$1 mln per day for a utility due to the expense of purchasing electricity on the open market to replace what was being generated by the plant. AmerenUE has pioneered the use of polyethylene (PE) as a new alternative to steel pipe ESW systems at its 1,200-MW Callaway plant. Polyethylene material does not corrode rust, rot, pit, tuberculate or support biological growth. It also has an outstanding field performance record for over half a century in water piping systems. Taking advantage of material science advances in bimodal polyethylene resins and a collaborative effort with a resin supplier, a pipe manufacturer, a pipe fittings manufacturer, an engineering contractor, and a primary construction contractor, AmerenUE engineers and construction teams have successfully replaced the carbon steel ESW pipe system at Callaway with a new class of bimodal high-density polyethylene (HDPE) pipe. The ESW pipe systems at Callaway hold and transport service water drawn from the reservoir pond inside the plant. Since the plant started operations in 1984, the original buried carbon steel water pipe systems have been continually susceptible to corrosion, fouling, rusting, and microbiologically induced corrosion, leading to pipe integrity issues such as pinhole leaks, pitting, and other localized forms of degradation. HDPE pipe was attractive for several reasons: • Is leak-free when produced properly, even at joints, which can be as strong and leak-free as the pipe itself through use of the heat fusion joining technique. • Is corrosion and chemical resistant: It does not rust, rot, pit, corrode, tuberculate, or support biological growth. • Offers seismic resistance, in that it can safely accommodate repetitive pressure surges above its static pressure rating and is well suited for seismic loading due to its natural flexibility. • Is easier and more cost-efficient to install than carbon steel. After an evaluation of available options, and based on the service condition and stringent requirements for HDPE pipe performance, the Callaway team selected CONTINUUM DGDA-2492 Bimodal Polyethylene Resin from Dow as the raw material for its new ESW secondary water pipe system. The resin has >10,000h PENT, more than 20 times better than the most stringent ASTM SCG requirement for PE4710 (a higher performance standard for HDPE pipe); it meets and exceeds the requirement at the adjusted higher stress intensity. A total of 168 pieces of fusion joint samples were tested using Nuclear Regulatory Commission (NRC)-recommended test methods. All joints passed the test without a single failure. HDPE is much less expensive to install than carbon steel piping. In addition, it does not corrode and is less susceptible to internal fouling. It can withstand a normal operating temperature range of up to 140°F (60°C) including short-term accident transients up to 176°F (80°C).