Calvert Cliffs Nuclear Power Plant - Executive Summary |
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EXECUTIVE SUMMARY The Calvert Cliffs Nuclear Power Plant (Baltimore Gas and Electric Company) is located 2 miles north of Lusby in Calvert County Maryland. The facility is a nuclear powered steam-electric power plant (SIC 4911). The facility was built into Calvert Cliffs but the upper topography of the site is generally flat or slightly sloping toward the Chesapeake Bay. The site is approximately 2300 acres in area and is mostly forested. The areas surrounding the site are mostly forested with some residential development. All storm water and process water is discharged into the Chesapeake Bay. The area is not serviced by a publicly owned sewer system. The on site wastewater treatment plant treats wastes from facility sinks and bathrooms. The site is covered by NPDES Permit 92-DP-0187, effective June 16, 1994. As a nuclear power facility, Calvert Cliffs has well established release prevention programs and emergency response capabilities. Calvert Cliffs accidental release prev ention policy involves a unified approach that integrates technologies, procedures, and management practices. All applicable procedures of the Nuclear Regulatory Commission (NRC) and the U.S. Environmental Protection Agency (EPA) Prevention Program are adhered to. The emergency response policy involves the preparation of response plans which are tailored to the emergency response services available in the community, and is in compliance with the EPA Emergency Response Program requirements. EPA requires this accidental release prevention plan for Calvert Cliffs Ammonia Hydroxide (NH3OH) usage. Ammonia hydroxide is used at the plant as an additive to the feed water system in the secondary steam cycle to maintain the pH of the water within a required band. This pH requirement is maintained to minimize the corrosion of the system piping which extends the life expectancy of the system piping and components and reduces piping failures. Ammonium Hydroxide, 28% to 30% concentration, is sto red in a 8500 gallon, seismic class 2 above ground, doubled walled, high density, cross linked polyethelene tank secured by steel cables to a seismic class 2 concrete pad. The inner tank has pressure relief protection that relieves to the outer tank and a ammonia vapor sensor in the outer tank with an alarm. The outer tank capacity is 10,000 gallons. The tank discharge line is connected to the tank with a flexible coupling to allow for tank creep. The tank is surrounded by barriers to prevent accidental vehicular contact with the tank. The tank is filled from a tanker truck. The procedure for filling the ammonia hydroxide tank is the Chemistry Procedure CP-414, Filling the Bulk Chemical Storage Tanks. When the driver transfers the contents to the storage tank, a second person, fully dressed in protective equipment is at the transfer location to provide assistance and/or summon help should a leak or spill occur. The site maintains a large supply of spill control equipment in a desi gnated location and maintains personnel on-site at all times who are trained to respond to fires, spills and medical emergencies. The site has a strong Spill Prevention Control and Countermeasures Plan (SPCC) that defines actions to be taken during spills and a strong Emergency Response Program which comes into affect if the safety of plant personnel or the public is threatened. The tank is regularly inspected and those inspections are documented. Any operational or maintenance deficiencies are documented and repaired in a timely fashion. Training at the plant is a continuous process throughout the year. Emergency Response training is conducted in job task groups. Each job task group is trained annually. EPA requires atmospheric modeling of hypothetical releases amounts for determining off site consequences. The off site consequence analysis includes consideration of two ammonia release scenarios, identified as "worst case release" and "alternative scenario". The first scenario is d efined by EPA, which states that "the owner or operator shall assume that the maximum quantity in the vessel is released and vaporizes over 10 minutes," due to an unspecified failure. The alternative scenario is defined as "more likely to occur than the worst-case release scenario and was selected by careful review of ammonia process operating experience." Standard EPA atmospheric dispersion modeling was performed to determine the distance traveled by the ammonia vapor released before its concentration decreases to the "toxic endpoint" selected by EPA of 0.14 mg/ l, using the Emergency Response Planning Guideline Level 2 (ERPG-2). This is defined by the American Industrial Hygiene Association (AlMA) as the "maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action. " The residential population within the radius corresponding to the toxic endpoint distance has to be defined, "to estimate the population potentially affected". The worst-case release scenario at the Calvert Cliffs Nuclear Power Plant involves a complete failure of the 8500 gallon ammonia hydroxide tank (a total of 19,000 lb. of ammonia). The off site consequence analysis for this scenario used worst-case release scenario conditions pre-defined by the EPA, namely release of the entire ammonia tank contents as a liquid turning vapor in 10 minutes, and use of the ERPG-2 as the toxic endpoint. EPA mandated meteorological conditions, assume a Stability F, wind speed 1.5 meters per second, an average air temperature of 77 oF, and average humidity was used. When the atmospheric dispersion modeling for the worst case scenario was performed using the EPA assumptions, a distance to toxic endpoint of 0.4 miles (2112 feet) and an estimate of residential population potentially affected of 0 was o btained. The most likely alternative release scenario involves the rupture of the flexible connection connecting the supply truck and the ammonia tank during a normal filling evolution. The amount of ammonia released is 3200 pounds, over a duration of one minute. Chemical specific prevention steps include use of a respirator, worn by the operator during ammonia tank filling evolution so if the transfer line ruptured the operator could push the remote shut off valve switch within 1 minute. Toxic endpoint distances at ERPG-2 levels were obtained. The typical meteorological conditions assumed a Stability D, wind speed 3 meters per second and average air temperature of 77oF. The estimated distances traveled to the toxic endpoints is 0.1 miles (528 feet). Results Summary Worst Case Alternative Ammonia Released 19,000 lbs. in 10 min. 3, 200 lb. in 1 min. Off Site Impact Distance 0.4 miles (2122 ft) 0.1 miles (528 ft) Number of Residential Public Receptors 0 0 No residential public rece ptors were identified in the Worst Case and the Alternative scenarios. Nuclear Regulatory Commission requirements determined that an ammonia release would not affect safe plant operation. Should a release happen, the realistic public concern is for the probability of fisherman on boats in the Chesapeake Bay near the plant intake structure and visitors at the plant visitors center. Calvert Cliffs emergency response procedures would have personnel evacuate these areas if a significant ammonia release occurred. The accidental release prevention program is based on the following key elements: 7 Use of modern equipment and construction planning 7 High level of training of the operators 7 Preventive maintenance program 7 Use of state-of-the-art process and safety equipment 7 Required use of accurate and effective operating procedures 7 Performance of a hazard review of equipment and procedures 7 Implementation of inspection and review programs No accidental releases of ammonia have occur red at this facility in the past five years. The facility has an emergency response program, which has been coordinated with the Calvert County Emergency Operations Plan. This program includes an emergency response decision tree and a notification plan. Emergency response drills and drill evaluations that include the Calvert County Emergency Operations Plan are conducted annually. Emergency operation and response procedures are also reviewed at that time. |