The importance of water chemistry

Nuclear power plants (NPP) generate nearly 20% of the total electricity in the U.S. and nearly 30% in the E.U. In NPPs, water in secondary and cooling systems controls the heat created from the fission of radioactive isotopes, to produce steam, which is used to generate electricity. NPP water chemistry is important for the maintenance of nuclear safety, major component reliability, and the overall economic viability of plant operation. Each nuclear power plant has a set of water chemistry matrices that are often specific for that plant and usually based on the water chemistry history and metallurgy of the plant. 

In general, the typical matrices are:

  • Pure water
  • Pure water with amine additives
  • Borated water
  • Closed cooling water (with high nitrite concentrations)
  • Environmental samples (effluents, soils, air, etc.)

Reagent-Free Ion Chromatography has been adopted in most NPPs due to its ease of use and improved detection limits, which make for a good fit with the typical matrices and analytes which need to be monitored in this industry. 

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Pure water

The chemistry of the feed water used in NPPs must be strictly controlled in both the primary and secondary systems in order to protect against corrosion, which can compromise the integrity of power plant components leading to faulty and hazardous operation. Identification of ionic contaminants in NPP water is critical for the identification and prevention of corrosive conditions and ion chromatography is an indispensable technique to identify the individual ionic species at sub- to low-μg/L concentrations.

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Pure water with amine aditives

Corrosion inhibitors and oxygen scavengers are added to control pH and create a reducing environment in both liquid and vapor phases of an NPP cooling system. Morpholine and ethanolamine (ETA), the most commonly used organic amines in E.U. and U.S. NPPs, respectively, minimize corrosion by maintaining the water and vapor phase pH between 9.5 and 9.8. Ion-exchange chromatography with suppressed conductivity detection is a well established method to determine μg/L to mg/L concentrations of common cations and amines; therefore, it is the method of choice in the NPP industry. 

Borated water

Boric acid is used in pressurized water reactor (PWR) power plants to control the nuclear reaction, because boron is a good neutron absorber. In PWR plants, measuring anionic contaminants in borated waters is an important part of corrosion monitoring.

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Closed cooling waters

In NPPs, water in secondary and cooling systems controls the heat created from the fission of radioactive isotopes, to produce steam, which is used to generate electricity. Stress-corrosion cracking and flow-assisted corrosion in the NPP boiler, secondary, and cooling systems can cause increased maintenance time and cost, and loss of power generation. Therefore, it is important to minimize corrosion in NPPs to avoid or reduce these associated events. Ion chromatography is the method of choice for the determination of potentially corrosive ionic impurities that include fluoride, chloride, and sulfate.

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Environmental samples

Ammonium and organic acids from the degradation of morpholine, ethanolamine, and hydrazine accumulate in the secondary and condenser water systems of nuclear power plants (NPPs), which require periodic flushing and blowout. This wastewater effluent, regulated by national wastewater discharge permits, limits amine discharges at levels specified for the individual NPP that range from low μg/L to low mg/L concentrations. Therefore, a sensitive method, such as ion chromatography, is needed to determine μg/L concentrations for compliance monitoring.

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