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Keeping it safe and cool

Oct 27, 2009 | Phil Fisher | The Courier

Safety for employees
ANO's last lost-time accident occurred nearly seven years ago on May 18, 2000. On Dec. 19, 2005, the site surpassed a milestone of 10 million hours worked without a lost-time accident. ANO has not had one since. The meter is still running. This positive run in industrial safety is closing in on the 13 million-hour mark.
ANO was the first site in the nuclear energy industry to join the Occupational Safety and Health Administration's Voluntary Protection Program known as VPP. When it comes to measuring industrial safety performance, VPP provides an excellent basis for assessing safety performance within an industry. Established in the early 1980s, this program provides an industry-by-industry benchmark in industrial safety for comparison of a worksite's performance to its industry's average.
VPP has three levels. The highest designation in industrial safety is the program's Star level. ANO entered the program in 1996 at the Star level and has remained a VPP Star ever since.
Minimizing employee exposure to radiation
Safely managing radioactive material is part of doing business at ANO. Areas within the plant that contain radioactive material are designated as controlled-access areas. Access is limited to personnel trained and certified to work in radiation areas.
Training involves initial instruction and annual follow-up training to renew familiarity with related procedures and various aspects of radioactive material. Workers certified to work in radiation areas are equipped with sensitive dosimetry to monitor and measure radiation exposure while inside controlled-access areas. Federal limits for occupational exposure are set at a low level for worker safety.
Entergy has conservative, administrative limits for exposure that are considerably lower than federal limits to further ensure worker safety and regulatory compliance.


Structured corrective action program
The goal is to identify small issues before they become bigger issues. That is the reasoning
that drives ANO's Corrective Action Program.
With hundreds of sets of eyes among ANO's Entergy employees and supporting supplemental workers, chances are if something needs attention, no matter how big or small, it will be noticed.
ANO, like all Entergy-owned nuclear sites, employs a structured process for raising issues for management awareness and resolution. Condition reports (CRs) detailing issues for resolution are initiated online by making them immediately available for management review.


About the cooling tower
ANO's 447-foot tall cooling tower serves Unit 2, one of two nuclear steam-electric generating units at the plant site. The cooling tower's role is to provide cooling water for Unit 2's condenser. The condenser is where steam, that was used to spin the turbine generator for generation of electricity, is cooled so it becomes water. Once steam is condensed, it cycles back through the unit's two steam generators where it is heated to create steam again. This steam is then piped to the turbine-generator to create more electricity.
Although Unit 1 operates exactly like Unit 2, Unit 1 does not have a cooling tower. It gets its condenser cooling water directly from Lake Dardanelle.


How the cooling tower works
The basin of the cooling tower is 4 feet deep and holds 2 million gallons of water pumped from Lake Dardanelle.
Traveling through a pipe that is 11 feet in diameter, water from the basin is pumped at a rate of 450,000 gallons per minute to Unit 2's condenser. When the water reaches the condenser, it branches off into 35,600 titanium tubes - each tube is 30 feet long and about an inch in diameter. As water circulates through condenser tubes, the tubes are cooled.
Steam, with its energy spent after a trip through the turbine-generator, flows into the condenser and condenses when it contacts the cool tubes. Water inside the tubes absorbs about 20 degrees Fahrenheit of heat from this heat exchange. This heated water is then pumped back to the cooling tower so the cooling tower can do what it was designed for - removing heat from water.
Heated water returns to the cooling tower through another 11-foot pipe. The large pipe goes to the center of the cooling tower's basin then turns directly upward to a height of 45 feet; a point level with the top of the support columns at the base of the cooling tower. That is as high as the water is pumped. Water exits the large pipe at that point branching off into thousands of smaller tubes that extend out horizontally in all directions to points near the cooling tower's exterior walls.
Water is released from the tubes, creating tiny droplets. This increases surface area to maximize cooling capability as the water showers down 45 feet to the basin. During the 45-foot fall, water gives up about 20 degrees of heat. The reason it cools so rapidly is because of a 30-mile-per-hour natural updraft of air drawn in from the base of the cooling tower.
As water falls and air rises, a heat exchange occurs that makes rising air warmer and falling water cooler. The updraft is created by a chimney effect due to the height of the cooling tower and rising warm air.


Vapor plume is like a cloud
Rising above the cooling tower is a vapor plume created when cool air from outside meets with warmer air on the inside causing condensation that is visible like fog. This vapor is carried out the top of the cooling tower by the strong updraft. About 10,000 to 12,000 gallons of water per minute is released in the plume. Make-up water is pumped from Lake Dardanelle to maintain the desired level in the basin to support ongoing operations.
The plume is clean vapor, like a cloud in the sky. By design, water that circulates through the cooling tower is isolated from radioactive material to prevent radioactive contamination of the water or the plume. Plume density is determined by Unit 2's power level and outside temperature and humidity.
Children often call the cooling tower a cloud maker, which is an accurate description.