INTRODUCTION
In order to comply with federal and local regulations for air quality, utilities opting to chemically clean their steam generators will be required to estimate their gaseous chemical emissions. Because most chemical cleaning solvents contain hazardous air pollutants, strategies for limiting the exposure of workers and the public must be considered. Common methodologies for estimating the type and quantities of gaseous emissions for chemical cleanings, as well as appropriate methods for exposure mitigation, are discussed. Additional cautions regarding specific local regulations are also presented.
During power operation, the steam generators (SG) of nuclear power plants accumulate large quantities of deposits, primarily metal oxides. Additionally, some plants accumulate significant quantities of copper deposits due to the original use of copper-alloy components in the balance-of-plant systems. While the concentration of these species in the final feedwater is typically <1 ppb today, past operation with much higher impurity levels has left many plants with significant sludge inventories in the steam generators.
The accumulation of these deposit inventories can lead to several problems with SG performance, including steam pressure loss, decrease in recirculation ratios, and under-deposit corrosion of tubing. Because these problems can present significant challenges to the economical operation of the units, plants will often elect to remove the deposit inventory once any of these conditions arise. The method of choice for removing large deposit inventories has been chemical cleaning during a refueling outage.
Because the chemical cleaning solvents typically used for nuclear steam generators contain various volatile constituents, utilities and vendors performing chemical cleaning are required to calculate the potential releases to the atmosphere that will occur during the process. While several methods for estimating emissions are available, a selection that has been successfully applied in previous cleaning programs is summarized herein.
SAMPLE REGULATORY REQUIREMENTS
In general, air pollution regulatory requirements break down into species that impact the National Ambient Air Quality Standard adopted by the federal and local governments and exposure limits for personnel working on the plant site. With regards to ambient air quality, in the United States the 1990 Clean Air Act sets air quality limits relative to six criteria pollutants that are considered hazardous to the public and the environment. Other localities (i.e., Ontario, Canada) are governed by similar regulations issued by their Ministry of the Environment.
The six criteria pollutants covered by the Act are as follows:
? Ozone (produced by the reaction of Volatile Organic Compounds and nitrogen oxides)
? Nitrogen Oxides
? Sulfur Oxides
? Carbon Monoxide
? Lead
? Particulate Matter (including that produced through the reaction of nitrogen oxides, sulfur oxides, ammonia, organic compounds, and other gasses)
In addition to these criteria pollutants, the Clean Air Act also addresses 188 hazardous air pollutants that are known or suspected to cause cancer or other serious health affects. Several of these pollutants are also classified as Volatile Organic Compounds (VOCs), but may also include some chemical cleaning solvent constituents (e.g., hydrazine and methanol). As with the criteria pollutants, businesses generating these types of wastes must apply for an emissions permit or obtain an extension of the current utility permit.
It is important to note that while the Clean Air Act established national air quality standards, each sta
