Duke Energy Nuclear Employees Participate in Earth Day

Earth Day is April 22, 2015. Each April 22, for the past 45 years, citizens around the world have honored a commitment for a clean environment by hosting festivals, rallies and environmental activities, all with support  from a  world-wide community.

Duke Energy and its nuclear employees  also support a clean environment. Did you know that nuclear energy is America’s largest source of clean-air, carbon-free electricity, producing no greenhouse gases or air pollutants — 64 percent of carbon-free electricity is produced by nuclear energy.

In recognition of Earth Day this year, Harris Nuclear Plant near Raleigh, N.C., will be the host of local sixth graders for a program on nuclear, renewables and energy efficiency. This will be the first visit to the nuclear facility by many of these students.

Catawba Nuclear Station and Oconee Nuclear Station employees will be participating in roadside  cleanups.

Employees at Catawba Nuclear Station, located in York, S.C., including members of the Catawba chapters of Women in Nuclear (WIN) and North American Young Generation of Nuclear (NAYGN), will spend the afternoon picking up litter along the road to the plant, as part of adopt-a-highway program.

Employees at Oconee Nuclear Station, located in Seneca, S.C.,  in partnership with the Keep Oconee Beautiful Association (KOBA), will participate in the Adopt-A-Spot program by l doing a litter sweep along the roads near the plant’s entrances. In addition, Oconee Maintenance  Department employees  have “adopted” their own section of local highways as part of their commitment to the community and the environment.

trash

Duke Energy nuclear employees keep local roads clean.

 

Nuclear Fuels Engineers Are Masters of Interior Design

Nuclear power plants in the United States produce electricity 24/7 and are baseload generating plants. Baseload power refers to generating resources that operate continuously and provide reliable power to customers, only shutting down for scheduled refueling and maintenance.

Nuclear power plants use uranium fuel, in fuel assemblies, to produce heat through fission (splitting of atoms). When uranium atoms split, they release energy in the form of heat.

Uranium Fuel

Source: Nuclear Energy Institute

Source: Nuclear Energy Institute

Fuel
This heat is used to heat water for creating steam, which turns the turbine-generator to make electricity.

How a Nuclear Plant Works

Source: U.S. Nuclear Regulatory Commission

Source: U.S. Nuclear Regulatory Commission

During power operation, the nuclear fuel assemblies are located in the reactor vessel in a cylindrical arrangement called the reactor core. Just like an automobile, nuclear power plants are refueled on a regular schedule – normally an 18 or 24-month fuel cycle – meaning that every 18 or 24 months, the nuclear generating unit is shut down for refueling. Once shut down, about one-third of the nuclear fuel assemblies (the oldest assemblies) are removed from the reactor core and placed in the used fuel pool for storage. This fuel has typically been used in the reactor for four-and-a-half to six years.

Used Fuel Pool

Source: Nuclear Energy Institute

Source: Nuclear Energy Institute

The remaining fuel in the reactor is rearranged and combined with new fuel assemblies that replace the ones that were permanently removed – this makes up the reactor core for the next operating cycle. The arrangement of the fuel assemblies, known as the core design, is analyzed to provide for maximize energy use from each fuel assembly.

At Duke Energy, our in-house Nuclear Fuels Engineering group is responsible for designing and managing each nuclear reactor core to ensure the fuel is safely used and satisfies the energy requirements of the next operating cycle. This takes a comprehensive understanding of plant operations, careful monitoring and detailed fuel analysis. The effort to model, analyze, establish limits and provide data for operating the cycle is roughly an 18-month effort. However, if changes must be made, the team at Duke Energy has demonstrated its ability to adjust the core design in as little as a few weeks. This can only be accomplished because of the high degree of automation, streamlined processes and expertise of Nuclear Fuels Engineering.

In past years, most nuclear plants operated on 12-month fuel cycles. Over the years, these cycle times were extended due to improvements in fuel design, maintenance and operations. These improvements have allowed for fewer refueling outages and improved on-line reliability, which also results in less labor to refuel the plant and lower costs for our customers.

Below are cross sections of a nuclear fuel assembly and a nuclear reactor core design. In Duke Energy’s boiling water and pressurized water reactors, the fuel assemblies contain from 80 to 264 individual fuel rods. These assemblies are selectively arranged to create core designs of 157, 177, 193 assemblies for the pressurized water reactors and 560 assemblies for the boiling water reactors.

Cross section of typical fuel assembly (Each circle represents a fuel rod; color coding represents rod type)

Cross section of typical fuel assembly (Each circle represents a fuel rod; color coding represents rod type)

Cross section of typical reactor core (Each square represents a fuel assembly; color coding represents regions)

Cross section of typical reactor core (Each square represents a fuel assembly; color coding represents regions)

Although not unique, Duke Energy is one of only a few U.S. utilities licensed by the U.S. Nuclear Regulatory Commission to perform its own nuclear core design analyses. This in-house design has enhanced competitive fuel supply, resulted in more economical fuel designs and provided the ability to respond swiftly to changing needs. It also provides for a number of interesting and challenging career paths for the Nuclear Fuels engineers.

Duke Energy’s Nuclear Fleet Braves 2015 Cold Snap

NEI-Freeze-403x403-2

Photo provided courtesy of the Nuclear Energy Institute (NEI).

In the Carolinas, the fruit trees are blooming and the official start of spring is here.  It’s easy to forget that just a month ago winter came in with a vengeance and tested the company’s power delivery system.  Record cold temperatures were like an unwanted dinner guest – they came and wouldn’t go away.  In such cold weather, electricity demand increases dramatically as customers struggle to stay warm.  Duke Energy Carolinas set an all-time record for peak electricity demand at 21,101 megawatt-hours on Feb. 20, 2015, exceeding the previous all-time record of 20,799 megawatt-hours set on Jan. 30, 2014.

The company’s nuclear power plants played a pivotal role in providing power to residential, commercial and industrial customers during the cold snap.  The Duke Energy nuclear fleet operated at 100 percent power during the most challenging portion of the February deep freeze, providing 10,679 megawatts of electricity.

The stellar performance of the nuclear fleet is no “accident.”  While low fuel cost, minimal greenhouse gas emissions and low environmental impacts are well-known characteristics of nuclear power, its reliability and availability is sometimes overlooked.  Nuclear plants are refueled about every 18 months, in contrast to coal or natural gas plants which need a continual supply of natural gas or coal to run.  For the most part, nuclear plants operate uninterrupted day and night, rain or shine until the next refueling outage.

The availability of the Duke Energy nuclear plants during the February cold weather was a result of good performance by well-maintained equipment and well-trained personnel.  The company places a strong emphasis on equipment reliability through preventive maintenance and early diagnosis of potential equipment problems.  As frigid temperatures approached, special measures were taken at each nuclear plant to ensure availability.  As soon as company meteorologists identified the looming weather challenge, nuclear teammates began carrying out special actions to cope with the anticipated high demand.  Each nuclear site ran through cold weather checklists to ensure key components would not freeze or become inoperable as temperatures plummeted. One site postponed a planned refueling outage, while another delayed system testing and preventive maintenance to help meet demand. Delaying the outage alone provided more than 930 megawatts of electricity to customers when it was needed the most (to learn more about refueling outages, click here to read a previous article).

The 2014 Polar Vortex highlighted the value of nuclear plants in the Midwest and northeast in dealing with extreme cold weather.  Similarly, during the extended cold weather in February 2015, the Duke Energy nuclear fleet performed in an exemplary manner to help cope with an unprecedented demand for power.  These incidents emphasize the value of generating assets that can supply large quantities of power reliably around the clock and during adverse weather conditions.