THE FUTURE OF ELECTRICITY GENERATION

Advanced Boiling Water Reactions

With the world population nearly doubling in the past three decades, the present surge in electricity demand, and the projected increase of the global population, the importance of available energy cannot be underestimated. In the United States, the burning of coal accounts for approximately one half of all electricity generation, nuclear energy approximately one fourth of all electricity generation, and hydro, and gas roughly ten percent of the total electricity generation.

Recent environmental concerns about the effects of burning fossil fuels have sparked a renewed interest in low polluting energy sources. Despite frequent negative publicity surrounding the nuclear industry, nuclear power remains an attractive option. For nearly four decades, the nuclear power industry has been upgrading and developing light water reactor technology, and has been preparing to meet the future demand for energy. In Japan, Europe, and the United States, ten new nuclear reactor designs are at the advanced planning stages, most of which are based upon the light boiling water reactor, so-called because the coolant is ordinary water.

Two advanced boiling water reactors are currently operating in Japan. During construction, the foundation of the reactor pressure vessel of one of the plants can be seen.

Light boiling water reactors account for essentially all of the commercial nuclear power production in the United States. Since most of these nuclear power plants were designed when regulatory requirements and technology were changing quickly, most of the power plants in the United States are unique. With thousands of reactor years of operating experience and forty years of research and development, significant improvements to plant design have been made to improve safety, increase operating life, and minimize costly maintenance and refueling procedures.

The nuclear industry in the United States is committed to using consistent designs for future plants. In other nations nuclear programs built on standardized designs have proven to be very efficient. In France, over thirty 900 MW and twenty 1300 MW units have been built in the past twenty years, currently supplying approximately seventy-five percent of the nations electricity. The series of plants built in France reduce operating costs and construction time and costs, and have improved the efficiency of training, parts procurement, maintenance, and safety.

Specifically, General Electric has designed a large light water reactor that was certified in 1997 by the Nuclear Regulatory Commission. The plant is termed "evolutionary," as it is based on previous designs and operating experience and incorporate advances in new technologies. The plant is simpler to operate, easier to maintain, and less expensive to build. Perhaps most importantly, multiple studies have shown that the design is nearly one hundred times safer than the current plants in the United States.

Improvements in the safety of the ABWR designed by General Electric resulted in significantly more compacted designs: the volume of the ABWR building is approximately one third smaller than those of the present BWR buildings, resulting in less construction time and expenses. One of two General Electric ABWR in Japan was completed in just over four years, over three months ahead of schedule.

The control rods are now powered electrically and hydraulically. This redundant source of power to the control rods significantly reduces the chances of failure in terminating the nuclear reaction and allows for fine-tuning the plant to produce a given amount of electricity during seasonal extremes. The daily operations of the control rods use electrical power, which can be moved in 3/4" increments. Only three control rod drives need to be removed for service during each outage, and they are continuously flushed with fresh water to reduce contamination levels.

One further advance in the design includes ten internal reactor pumps replacing external recirculation pumps, eliminating piping and connections for increased safety and decreased costs. The pumps have proven to be very reliable and durable in Europe, and only two pumps need to be removed for servicing each outage. The internal reactor pumps are constantly flushed with clean water, decreasing the radioactive material that collects in the pumps.

The Reactor Pressure Vessel (RPV) is made of a nuclear grade low carbon steel alloy, highly resistant to cracking. A large portion of the vessel is made from a single forging, which reduces the over fifty percent of the welds and pipe supports in the system, thus reducing the main source of radiation exposure.

Part of the reactor pressure vessel is transported during construction of an advanced boilin water reactor in Japan.

Modern digital technology and fiber optics are used for control and instrumentation in the plant, significantly decreasing the amount of cabling in the plant and time required to build the plant. Four independent divisions of logic and control are used in the ABWR, utilizing four redundant multiplexing networks to insure plant safety. Fault tolerant controllers compare the result from simulated incoming signals to the expected output. If a controller detects a problem, the remotely distributed cards that contain the controllers for equipment and sensors can easily be replaced.

Excavation work must be performed prior to construction of the plant. Here, a Japanese is ABWR under construction.

Active safety systems have been incorporated into the new ABWR design, which consist of three redundant, completely independent systems. The systems are electronically separated: each division has access to its own sources of redundant electricity, including batteries and an emergency diesel generator. Further, the layout of the plant is such that the safety systems are physically separated by space and firewalls. Any disruption in one of the divisions will have no effect on the capability of the other two divisions. The systems have the capability of always keeping the reactor core covered with water. Because of this and the thermal margins in fuel designs, costly transients which require the plant to shut down have been reduced to less than one per year. The reactor has been fully automated in the event of coolant loss and the operators are not required to take action for 72 hours.

General Electric Advanced Boiling Water Reactor (ABWR) design.

The primary containment structure is the reactor containment vessel, and is made of a steel lining and reinforced concrete. The secondary containment structure is the reactor building, which is maintained at a negative pressure to keep any radioactive release from the outside environment. Great attention has been given to design the plant with maintenance in mind. For instance, the internal reactor pumps and control rod drives have been fully automated. Outside of the containment, handling devices remove the equipment by laying it on a transport device and moving it out through the equipment hatch. Shielded rooms that are dedicated for service to the specific piece of equipment are located just outside the hatch, where maintenance can easily be performed, which minimizes the radiation exposure to workers.

The thousands of years of operating experience and new technological breakthroughs are the driving force behind the design of the advanced boiling water reactors, with the goals of environmentally friendly, economical, and reliable nuclear power plants for electricity generation. Growing concern about pollution and global warming has led many individuals and nations to consider the nuclear industry as an excellent alternative for future power generation. Technological advancements and increased public awareness concerning nuclear power are critical to the success of the nuclear industry. Investments made by the nuclear industry in both technology and education will likely be seen in the near future.