On December 9, 1986, an elbow in the system ruptured, condensing cooling water at the Surry Nuclear Power Plant near Williamsburg, Virginia, killing four workers and losing tens of millions of dollars in revenue and maintenance costs. According to the Electric Power Research Institute (EPRI), corrosion occurred in the bends of the pipes of the feed pump. Pressurized water flashes into steam, scalding workers and shutting down the plant.
Power plants that use steam to generate electricity need water. Without it, they could not do the job. But water and steam are as complex as the blood in our veins and arteries. Therefore, water chemistry is a complex and important task for steam power plants. Water is the source of life for all coal from steam power plants, combined cycle gas or nuclear fuel.
A major research group on energy development has long been developing an aggressive plan for water chemistry for steam power plants. Basic electricity generation technologies have common problems with water. In general, water chemistry is one of our main methods of supporting the life of materials in a steam equipment.
Enterprise managers and operators are tasked with controlling impurities and other characteristics in the water that convert heat to steam and steam to electricity. Impurities can cause corrosion and cracking. Corrosion caused by oxidation on metal surfaces can corrode water flow and cause deposits elsewhere in the plant.
It can also cause deposits in the boiler, which reduces heat transfer and slows the flow of water through the system. This means that the plant is inefficient, as seen at the Surry plant, which poses a threat to the safety of workers. To better prevent these negative effects, water chemistry controls have changed considerably over the past 30 years. These changes are the result of the chemical community’s commitment to research and technological development. However, it is the responsibility of the plant operator to ensure that these changes are implemented in its factories. And as the industry’s workforce ages. More than ever, the next generation of operators knows the right chemical controls for water.
EPRI operators must focus on two main goals
- Corrosion crack: This may cause hose failure.
- General corrosion: can reduce heat transfer, reduce flow and cause material degradation.
The alloys found in condensing and feed water systems in power plants include carbon steels used in pipes, pumps and, in some cases, heat exchangers. Many systems still use certain copper-based alloys, from Admiralty brass and copper-nickel alloys (Cu-Ni) to Monel 400 series alloys, which are mainly used as feed water heating tubes. . Stainless steel alloys generally avoid the common corrosion mechanisms that afflict carbon steel and copper alloys. This is because a tightly adhered chromium oxide layer forms on the surface of the stainless steel, thereby protecting the stainless steel.
People tend to think of stainless steel as an ideal alloy to replace copper alloy water pipes. However, the Achilles heel of stainless steel is that chlorides and corrosive alkalis can cause stress corrosion cracking. Intergranular stress corrosion cracking was a major problem for nuclear power plants in the 1980s, although research led by EPRI has largely provided a solution to this problem.
Water chemistry is crucial for all steam power plants, while nuclear power plants have some unique challenges. This is due to the fact that the water of ordinary light-water reactors is in contact with fuel, which means that H2O transfers radiation. This complicates maintenance and can lead to contamination of personnel. Radiation also causes metal degradation and the circulation of water and steam in factories. This is important for extending the life of nuclear power plants, which the industry believes is crucial for their future.
Advanced nuclear design will also pose hydrochemical challenges. NuScale Power’s recommendations for small modular reactors. He said EPRI is paying close attention to the design of the NuScale reactor, including its impact on water chemistry.
Another chemical challenge is the use of hydrazine (N2H4). Fossil and nuclear power plant operators are using it in the steam cycle to reduce dissolved oxygen and corrosion. But this is a nasty chemical that is banned in Europe for carcinogenicity. Europeans have done some work on alternative chemicals, and EPRI’s role is to act as a collaborative engine, bringing together all the research, and putting a lot of effort into completing technical work to move to potassium hydroxide. Demonstrations may take place in 2020 or 2021.