Advanced reactors power TEPCO plant
The world`s first two GE ABWR nuclear units have gone into service at TEPCO`s Kashiwazaki-Kariwa plant
By Woodrow A. Williams
GE Nuclear Energy
A new chapter in commercial nuclear power began Nov. 7, 1996, when the world`s first advanced nuclear power plant, the Tokyo Electric Power Co.`s (TEPCO) Unit 6 at the Kashiwazaki-Kariwa nuclear power station, entered service. The 1,356 MWe power plant was built within four years and completed on schedule and under budget.
The TEPCO unit, an advanced boiling water reactor (ABWR) is the result of a development program that has spanned 18 years. A second ABWR, the K-7 Unit, achieved 100 percent power during startup testing in March 1997. It will enter commercial service later this year. When completed, TEPCO`s Kashiwazaki-Kariwa site will be the world`s largest nuclear station, with seven boiling water reactors (BWR) collectively generating 8,212 MWe.
Both TEPCO units are “first-of-a-kind” and, as noted, were built on budget and on schedule. The total construction schedule came to 48 months as measured from first concrete pour to continuous operation at 100 percent power. This experience bodes well for other nations contemplating the addition of nuclear power generation to their national grids.
TEPCO and other Japanese utilities have also announced plans to construct on the order of 10 more ABWRs in the early 21st century. In Taiwan, where there is a critical need for new electricity supplies, the ABWR was selected in May 1996 by Taiwan Power Co. for the first two units of its Lungmen project, which is expected to see commercial operation in 2004 (Unit 1) and 2005 (Unit 2). The ABWR was chosen in an international competition that featured other advanced light water reactor designs.
Nuclear power`s economic advantage
Globally, the demand for electricity will continue to grow for the foreseeable future, particularly in the developing countries with growing economies (Figure 1). In Asia, which has experienced rapid economic growth, the demand for electricity has been growing in some cases by more than 10 percent per year. This growth is expected to continue and, as a result, an additional 400 GWe of new power plant capacity will be needed by the year 2000.
A large percentage of the new power plants are expected to be baseload capacity. An advanced nuclear plant is an ideal baseload plant because a large percentage of its cost of electricity is fixed. Moreover, the nuclear fuel cost is very stable over long periods of time. This cost of electricity from a nuclear plant can be competitive with other, non-nuclear sources. Another key is that nuclear plants in Asia are being built on predictable four-year schedules at attractive costs.
Even in countries with lower fossil-fuel prices, electricity from advanced nuclear plants has an economic advantage. A comparison of the total life-cycle costs of different generation options on a levelized cost of electricity basis shows that the ABWR and a coal steam plant could be considered equally competitive. Plant costs and performance are based on current international market values and available technology. Fuel costs are based on local estimates, with escalation based on published Energy Information Agency forecasts. Economics are based on a utility, as opposed to a private developer, constructing and operating the plant. The key assumptions in these types of analyses are the cost of natural gas and the capital cost of the nuclear plant (Figure 2).
It should be noted that the cost of natural gas, particularly in developing countries, can be high. In this particular analysis, which was done for a country that must import fossil fuels, a coal, combined-cycle or nuclear plant could be selected on the basis of economics alone. However, with the many assumptions that must be made in an evaluation such as this, all options should be included in the energy mix. A policy of fuel diversity is particularly important when considering the many future uncertainties regarding fossil-fuel prices and environmental regulations.
Advanced reactors: approved and standardized
Developing nations contemplating nuclear power additions have the assurance of selecting advanced designs that have met stringent review prior to acceptance. The ABWR, for example, has been approved by both US and Japanese licensing authorities. While no new nuclear projects are contemplated in the US at present, GE and other suppliers have vigorously moved forward with advanced designs, clearing the way for possible future use for electric power generation in the US. The US Nuclear Regulatory Commission unanimously approved a design certification for GE`s ABWR last December.
At the time, GE called the commission`s action “a major step in bringing order and predictability to the nuclear power plant licensing process.” GE noted that endorsement and use of approved standardized designs should dramatically reduce the licensing/construction phase of new nuclear projects, bring order and predictability to the process and encourage US utilities to consider nuclear power among their options in meeting future electrical power demands.
TEPCO`s ABWR experience
“It has been demonstrated at Kashiwazaki-Kariwa Unit No. 6 that an ABWR can be built with a construction schedule of four years, fulfilling the target of improved safety and reliability, and also with dramatic improvement in economy,” comments Katsuya Tomono, executive general manager, Nuclear Power Program Operation for TEPCO. “I am hopeful that ABWR will play the leading role in power supply both domestically and abroad as the standard reactor for future BWRs.”
The commercial reality of the ABWR in Japan is a clear signal that light water reactors will continue to play an important role for the 21st century. The ABWR program actually began in 1978 when an international cooperative effort was formed to shape a reactor design for the future. TEPCO played a key role in directing the final ABWR design to meet its specific utility objectives. The ABWR design that evolved was based on technologies that were tested and verified through utility-manufacturer joint study programs and verification programs. Through these efforts, the ABWR was accepted as the next BWR standard design as part of the Japanese government`s Phase III improvement and standardization program.
ABWR objectives and features
In order to achieve an optimum design for the 1990s and beyond, the ABWR had the following key design objectives:
– provide enhanced safety and reliability;
– reduce occupational radiation exposure and radioactive waste;
– provide excellent operability and power maneuverability; and
– achieve greater economy in power production.
Enhanced safety and reliability
– Simplified primary system piping. The adoption of 10 reactor internal pumps around the periphery of the vessel bottom head eliminates the external reactor cooling loops used on earlier BWRs. Also, with no openings in the reactor vessel below the fuel region, this design ensures that the core and fuel always are covered and cooled by water during all design basis accidents.
– Diversity of control rod drive mechanisms. An electric drive system has been added to the existing hydraulic system to give finer control of power variations, and also to provide diversity and redundancy for reactor shutdown, thus increasing the safety margin.
– Optimized Emergency Core Cooling System (ECCS). The ABWR has enhanced safety by separating the ECCS into three physically and electrically independent divisions, thus always maintaining a redundant backup system.
– Wet, pressure-suppression containment. The wet, pressure-suppression containment requires a 30 percent smaller volume to contain the discharge from a vessel blowdown.
– Passive severe accident mitigation. Passive accident mitigation features have been added and, as a result, the calculated core damage frequency is reduced from 2 x 106 to 1.7 x 107, improvement by a factor of 10. No operator action is required for up to 72 hours after a design basis accident.
Radiation exposure/radioactive waste
– Reduction of radiation sources. The expected occupational exposure will decrease from the current level of 350 person-rem/yr to less than 100 person-rem/yr because of a number of design changes.
– Reduction in radioactive waste. The amount of low-level waste generated will decrease from the current level of 800 drums to an expected 100 drums per year as a result of design changes for the ABWR.
Excellent operability and maneuverability
– State of the art instrumentation and control system. Optical multiplexing of signal transmission significantly reduces cable volume. A fault-tolerant triplicate control system allows single-channel malfunction while data are still being retrieved by other channels.
– Advanced man-machine interface. The control room features a one-man, sit-down operation with touch-screen control and large mimic plant system displays. Plant operation is automated from startup through full-power operation. Artificial intelligence assists in plant status diagnosis.
– Greater maintainability. Inside the reactor building, equipment at all levels is accessible by stairs and platforms which encircle the vessel and equipment.
– Reduced construction cost. The building volume and materials required are much reduced, including shorter wire and cable runs, less piping and reduced high-voltage alternating current ductwork.
– Reduced operating cost. The design reduces the inspection frequency of key components.
New construction technologies
The ABWR also introduced new construction technologies to the industry, the result of TEPCO`s intensive effort to shorten construction schedules, improve quality and provide greater safety for workers and equipment. The new construction technologies helped support another key objective, the reduction of construction costs. TEPCO`s approach to new construction technology was two-pronged: development of the plant and building design on an integrated basis, employing extensive three-dimensional computer aided design (3-D CAD); and the use of innovative construction methods, such as all-weather construction and large-block module construction assembly on site.
The 3-D CAD system used at K-6 and K-7 enabled all design processes, from basic design to final implementation, to be carried out on an integrated basis. The system was also used for the preparation of construction execution plans and as a source for “as built” information for overall configuration management upon commercial operation. The all-weather construction method was another major contributor to the exemplary construction schedule. A temporary roof and walls were used over the key construction area, thus creating a factory-like environment even under the site`s severe winter weather. Monorail hoists and a temporary overhead crane were laid out to cover the entire building area.
Another innovation was large-block modular construction. This enabled construction planners to perform various tasks in parallel by assembling equipment and structural components into large blocks at the factories or in the site`s assembly yard. This technique helped cut the construction schedule, reduced site work loads and improved working conditions.
Pre-operational testing and inspection
This phase of plant construction can be classified into four groups: First, verification tests were performed in order to confirm design performance and functions of installed components, such as “first-of-a-kind” equipment. Second, system tests were completed in order to confirm system performance and functions before fuel loading. Third, pre-operational tests were conducted in order to confirm plant safety and operability. The fourth category covered pre-use inspections required by regulatory authorities. At each stage of pre-operational testing and inspection, test data were evaluated and compared with analysis data and design criteria. Thus, safety was verified at each stage. Overall, the pre-operational testing of Units K-6 and 7 was performed smoothly and successfully.
New main control panel
The ABWR control panel is another key feature of the Kashiwazaki-Kariwa nuclear station. Its man-machine interface is improved based on analyses of the operator`s workload and human factors considerations that adopt state-of-the-art instrumentation and control systems. The panel incorporates one-man operation from a seated position, information sharing among the crew via a large display panel and a new alarm processing and display system. A full-scope operator training simulator was installed 1.5 years before fuel loading at K-6, and the education and training of operators has been fully conducted.
The ABWRs at the Kashiwazaki-Kariwa plant are fully proven technologies and feature improved economy with enhanced reliability and safety. In a message commemorating the start of Unit K-6 last year, TEPCO executive vice president Ryo Ikegame, said: “It gives me great pleasure to mark the start of commercial operation of the world`s first ABWR. As an individual who has been directly and very closely involved in this project since the very early stage of developing the concept of ABWR around 20 years ago, I have a deep attachment to this project. I should like to take this opportunity to thank all of those who have participated in this development, especially the members of Hitachi, Toshiba and GE, who have associated themselves with this project for so many years, for all their efforts that have brought about this memorable event. Also, my earnest wish is to see ABWR accepted in the world market as the new standard for the light water reactor.”
Control room for the two-unit Kashiwazaki-Kariwa ABWR power plant.