Farrokh Najmabadi, Mark S. Tillack
Fusion Energy Research Program, University of California, San Diego, La Jolla, CA 92093-0417
Lester M. Waganer,
McDonnell Douglas Aerospace, St. Louis, MO, 63166-0516
and the ARIES Team
Fusion energy research has made enormous progress during the past decade, culminating with the proposed ITER device. ITER is expected to produce a significant amount of fusion power and become the central element of the world-wide fusion research effort. The next step is to progress from an experimental reactor to that of a demonstration power plant which will assure the electric power community that fusion is ready to enter the commercial arena. The Starlite Project, therefore, was initiated to investigate the mission, requirements and goals, features, and R&D needs of the Fusion Demonstration Power Plant. The Fusion Demo must demonstrate that a commercial fusion power plant would be accepted by utilities and industry (i.e., it is affordable and profitable) and by the general public and the government (i.e., it has superior safety and environmental features). Therefore, as the first step in the Starlite project, a set of requirements and goals for commercial fusion power plants were developed. These commercial requirements and goals were then used to arrive at a mission, quantifiable top-level requirements, and goals for the fusion demonstration power plant. Using these requirements and goals, assessments were made of the principal options currently envisaged for a tokamak-based fusion Demo power plant.
The long-term goal for fusion has been the production of electrical power - a secure source of abundant, affordable electrical power with little or no environmental impact. The demand for substantial increases in electrical power requirements has been forecast for decades. Conservation and use of relatively inexpensive fuel have reduced the need to develop new electrical energy sources, affording more time for the development of fusion. But environmental concerns have severely curtailed many of the previously viable electrical sources. Improved power plants using existing energy sources are meeting with increasingly difficult regulations to continually improve both local and global environmental impacts. Thus there exists a window of opportunity to become a substantial provider of electric power. Fusion offers the promise of an abundant energy source that is not tied to national resources and will have only a minimal impact on the environment.
During the past decade, enormous progress has been made toward demonstrating the necessary physics and engineering goals in experiments such as DIII-D, TFTR, JET, and JT-60. The proposed ITER device will continue to advance the state of knowledge toward a clearer understanding of the creation, control, and use of large-size tokamak plasmas. The next step is to progress from an experimental reactor to that of a demonstration power plant to assure the user community that fusion is ready to enter the commercial arena of electrical power generation.
Paramount to a project such as the U.S. Fusion Demo is understanding the customer needs. From that, one can derive a qualitative mission statement which describes the intent and purpose of the project and how it addresses customer needs, and the requirements which translate the customer needs into quantitative measures. Based on experience and the existing data base, conceptual designs are then developed and used to refine the requirements, as well as to identify critical issues and R&D needs. An R&D implementation plan is then produced and implemented. This concept development phase may be repeated as further conceptual designs are developed, based on the new data and new R&D, until sufficient confidence is achieved to proceed with the preliminary design phase of the project.
In this context, the Starlite project was commissioned to initiate the process by investigating the mission, requirements and goals, features, and key R&D requirements of a fusion demonstration electricity-generating power plant. The project includes broad participation from several organizations in the U.S. engaged in fusion research, including universities, national laboratories and industrial partners. A fully integrated approach to power plant analysis and design was adopted. In addition to the concurrent emphasis of customer needs in product development, broad technical capabilities are applied to examine the full range of power plant issues in a self-consistent manner - from plasma physics and basic material behavior to component performance and complete systems analysis. Special task groups were formed to deal in depth with the issues of costing, safety and licensing, and RAMI (Reliability, Availability, Maintainability and Inspectability), which have such a major impact on the potential for fusion to play a significant role in the future energy supply mix for this country.
Accordingly, a set criteria for fusion power has been derived based on interaction and advice from the utilities and industry. These criteria were then used to develop a mission statement as well as top-level system requirements for the Fusion Demo. This work is reported here. Several candidate options for the physics operating regime as well as the engineering design of various components (e.g., choice of structural material, coolant, breeder) have been developed and assessed against the top-level Demo system requirements and reported elsewhere in these proceedings.
REQUIREMENTS AND GOALS FOR COMMERCIAL FUSION POWER
A demonstration power plant will be built and operated in order to assure the user community (the general public, utilities, and industry) that fusion is ready to enter the commercial arena of electrical power generation. Thus, the requirements and goals for acceptance of fusion power must first be defined.
Power producers (utilities and independent power producers) and the industries that manufacture the power plants demand that any source of energy will be a commercial success (i.e., affordable, profitable, and meeting public acceptance). The general public and government agencies ask for an energy source which is safer, generates little or no waste, does not deplete limited natural resources, has minimal effect on the environment, and can provide adequate energy to satisfy a significant portion of the demand at a competitive price over the next century. These are common goals shared by all other existing and alternative energy sources. Fusion power, therefore, should meet these goals.
Fusion power in its present embodiments will result in a large, central-station power plant. At present, the investor-owned, public electric utilities best represent the customers for this type of power plant. To better understand the needs of this class of customer, the Starlite Project solicited several large public utilities and support industries to help define the mission of fusion. Several utilities and industries agreed to help establish and participate in a Power Plant Studies Utility Advisory Committee. This committee provided advice to help formulate the mission and goals for fusion in general, and for a fusion demonstration power plant in particular. The case for an attractive fusion power was developed, as shown in Table I and discussed below. These desirable attributes were developed to be offered to a decision-making body which will be asked to choose a fusion power plant over other alternatives which are available at that time. A similar set of criteria has been developed by the EPRI fusion working group .
Cost advantage over other available central station options: Because fusion is a new technology in the energy marketplace, it must have a cost advantage to offset the inherent technical risk of a new technology; otherwise, it will never be widely endorsed. It should be noted that this cost reflects a complete life-cycle cost; that is, it includes costs associated with other elements of the case (e.g., costs due to delays in licensing and/or public opposition to an evacuation plan). Fusion should achieve its full safety and environmental potential for it to have a cost advantage over other sources of electricity.
Eased licensing process: To circumvent the difficulties experienced by fission, fusion should be easy to license by the national and local regulating agencies. Only through the use of low-activation materials and failure-tolerant design will fusion power plants be designed such that the consequences of an accident are minimal.
No evacuation plan needed: In order to gain public acceptance and support, fusion should demonstrate that it does not disturb the day-to-day life of the public. Fusion must be perceived by the public to be inherently safe. To support this criterion, it was recommended that the fusion power plant should not require a site evacuation plan.
No high-level waste produced: An important public demand is that new technologies not provide a burden for future generations; that is, waste generated should be either recyclable or disposable in a time frame which is within a human life span. Therefore, to gain public acceptance, fusion should not produce long-lived high-level waste.
Reliable, available, and stable electrical power production: Because fusion is a new technology, it must demonstrate that it can achieve the necessary degree of reliability. This criterion should be addressed early on in the development path of fusion power. Today's experiments are, by their charter, experimental devices and are not intended to provide detailed engineering data to support the design, construction, and operation of a power plant. Experiments with burning plasmas will provide some necessary data, but the design and construction cycle of these devices are so long that data can be obsolete by the time they are obtained. This set of requirements is perceived as the most difficult to achieve in a time-constrained development program.
The remaining criteria are foreseen as reasonably easy for fusion to achieve but are significant attributes for an electrical power source. The desire for no atmospheric impact is a powerful requirement in light of the difficulties of competing energy sources. No scrubbers, containment vessels, or special safety systems will be needed in fusion plants. The self-contained fuel located on site is a powerful advantage that circumvents strikes, natural calamities, and adverse supplier actions. This helps the utility better control their self destiny. Fuel availability is similar in that all elements in the fuel cycle are in abundant supply with no critical resource shortages. The last two criteria deal with how well the fusion plant will function in conjunction with the power network and the time-varying energy demand. There appears to be no difficulty in designing a fusion plant to load-follow. Availability in a range of sizes is limited only by the fact that smaller sizes would tend to be more costly on a COE basis.
If there were reasonable assurances that this set of high level criteria could be met by a demonstration power plant, then the decision to purchase a commercial fusion electrical power plant would likely be positive. Thus the intent for the Demo power plant is to use these criteria as guiding features to help structure its mission and goals.
Based on the above requirements, a set of quantitative top-level requirements for fusion power plants has been derived and is listed in Table II.
Requirement Demo Commercial 1. Must use technologies to be Yes Yes employed in commercial plant 2. No evacuation plan required 1 rem 1 rem Dose at site boundary total total 3. Generate no Class C Class C radioactive waste greater than: 4. Must demonstrate Yes Yes public's day-to-day activities not disturbed 5. Must not expose workers to a Yes Yes higher risk than other power plants 6. Demonstrate a closed Yes Yes tritium fuel cycle 7. Net electric output 75% of Not must be greater than: commercial applicable 8. Must demonstrate operation 50% 50% at partial load conditions 9. Demonstration of robotic or Yes Yes remote maintenance of power core 10. Demonstrate routine operation 1 1/10 with less than (x) unscheduled shut- downs per year including disruptions 11. Cost of electricity must be 80 65 (GOAL) competitive (in 1995 mill/kWh) 90 80 (REQMT)
MISSION, REQUIREMENTS AND GOALS FOR THE FUSION DEMO
The prior section discussed the goals needed for the commercial plant to be accepted and to succeed. On the other hand, the Demo must "demonstrate" those attributes that would convince the utility or their investors and the public that this new technology, for long periods of time, is safe, economical, and does not harm the environment. The Demo need not meet 100% of all commercial power plant goal objectives, but the risk in eventually meeting those goals in a power plant must be acceptable. The public is very concerned about public safety; thus this goal must be demonstrated to a high level of confidence, i.e., low risk. The economics goal would be difficult to meet without significant government or investor subsidies to artificially lower the capital and operating cost. Thus the owner/operator of this demonstration power plant must be able to operate the plant on the power grid for long periods of time and gain both operational experience and profit for the sale of electricity. The public perception of the interaction of the first fusion power plant with the environment will be a highly visible public issue. This is another area where the Demo plant must convincingly demonstrate over long time periods that fusion is a "good neighbor". There will have to be high visibility of all safety and environmental issues to comfort and sustain the public.
Based on the above arguments, the Starlite project has adopted the following mission statement for the U.S. Fusion Demo Power Plant:
The Fusion Demo demonstrates that fusion power is a secure, safe, licensable, and environmentally attractive power source that is ready for commercialization at an economically superior total cost.
The detailed elements of the Demo mission statement are summarized below:
1. Technology and Performance Demonstration: Demo should use the same technologies as planned for commercial power plants. Introduction of a new technology (e.g., different plasma operating regime, coolant, or structural material) would be inappropriate, as this would require that a new development path be initiated.
2. Integration and Scalability Demonstration: Demo should demonstrate all systems working as an integrated unit. The Demo should be large enough so that the step to the first commercial power plant is small.
3. Economics Demonstration: Initiation of the Demo construction requires clear demonstration that the successful operation of the Demo will lead to a economically superior power plant. Operation of the Demo should demonstrate that construction, operation, maintenance, and decommissioning costs are in the forecasted range, and that the power plant would have a competitive life-cycle cost of energy.
4. Safety and Licensing Demonstration: Demo should demonstrate that fusion power is safe. Demo should conduct demonstration testing, as an element of certification by regulatory agencies, which enhances public acceptance and will support timely licensing. Demo should provide the data base necessary to obtain certification by the regulatory agency of the standard plant in order to ensure timely licensing for commercial plants and instill investor confidence.
5. Waste-Disposal Demonstration: Demo should demonstrate that fusion generates only low-level waste and all waste can be recycled and/or disposed of at an acceptable cost.
6. Decommissioning Demonstration: Demo should demonstrate that decommissioning can be performed at an acceptable cost.
7. Reliability Demonstration: Demo should demonstrate that fusion power plants can operate within the prescribed performance envelope (load following, start-up and shutdowns, load ramp rates, endurance operation) with unscheduled internal events not exceeding the designed and prescribed values.
8. Maintainability Demonstration: Demo should demonstrate that fusion power plants can be maintained (both scheduled and unscheduled maintenance) within the prescribed cost/schedule envelope. This is necessary to both achieve the desired availability and eliminate the risk of a plant write-off because of a severe internal accident.
9. Availability Demonstration: Demo should demonstrate that fusion power plants meet or exceed availability targets that are competitive with other sources of electric energy.
10. Operability Demonstration: Demo should demonstrate ease of operation. Demo should demonstrate that routine emissions from the plant are all below allowable values.
11. Industrial Supplier Demonstration: Demo should stimulate an industrial infrastructure which is prepared to supply fusion power plants on order. Demo should yield the industrial commitment to deploy the first series of commercial power plants.
12. Power-Producer Interface Demonstration: Demo should stimulate establishment of a power producer (user) interface which is prepared to provide operational support programs and support generic regulatory interactions in order to ensure timely penetration of fusion power plants into the market.
The above mission elements together with the requirements for fusion power are used to develop a set of top-level requirements for the U.S. Fusion Demo, also given in Table II and described in more detail in Ref. .
ASSESSMENT OF ALTERNATIVES
Based on the requirements described above, assessments have been performed for both physics and engineering options for a tokamak fusion Demo. These assessments consider not only the ability of optimized designs to meet the top-level system requirements, but also the uncertainties which exist in our ability to predict the key performance parameters. The magnitude of extrapolations from the present database and the associated R&D requirements are identified to help guide future research.
Specific physics design requirements for the plasma and its support systems have been established. Performance parameters were determined that can be used to select the most attractive and credible plasma concept among five proposed candidates . These options include first stability, second stability, and pulsed operations, which are modified versions of the ARIES-I, ARIES-II, and PULSAR power plant designs, respectively. The other two concepts analyzed are the reverse shear mode, based on TPX, and the low aspect ratio tokamak. Results of these physics studies in the initial phases of the Starlite project are described in more detail in Ref. .
In this early phase of the U.S. Demo project, detailed engineering designs have not yet been developed. Instead, various classes of design options have been examined and their potential to meet the Demo requirements assessed. These options include material choices for the structure, breeder and coolant. The design space for an attractive tokamak fusion power core is not unlimited; previous studies have shown that advanced low-activation ferritic steel, vanadium alloy, or SiC/SiC composites are the only viable candidates for the primary in-vessel structural material. In order to provide a framework for this assessment, these three material classes were used to distinguish engineering design choices. Results of the engineering assessment are reported in more detail in Ref. .
This assessment methodology is completely generic and can be applied to the assessment of any potential Demo or power plant concept, including other confinement approaches or other design options not considered in the study.
Several of the most critical aspects of a Demo power plant are given special attention in this study. These include (1) fusion economics and costing, (2) safety and licensing, and (3) reliability, availability, maintainability and inspectability (RAMI). These system-wide issues cross traditional borders between physics and engineering of individual components and systems. Historically, they have been given inadequate attention and/or have been based on fission and other technologies without adequate updating and adjustment for the unique attributes of a fusion power plant. Yet, they are central issues which will play a primary role in determining the ultimate acceptance of fusion as an electric energy source.
A. Fusion Economics and Costing
Fusion must be economically competitive at the time of its introduction into the marketplace or no one will buy it. The economic targets for fusion Demo and commercial power plants have been established based on extensive examination of energy forecasting models and the expected trends for competing energy sources . The requirements specified in Table II resulted from these investigations. One of the most difficult but important jobs of economic forecasting is to include all relevant costs associated with an energy source. Historically, many of the costs associated with power production (such as R&D costs, government subsidies, decommissioning, pollution of the environment) have been "externalized" in the balance sheet, often resulting in misleading conclusions. Current trends in deregulation of the industry and expanded consideration of environmental impacts suggest that these costs will have to be internalized by future decision-makers. Here we attempt to explicitly identify these costs whenever possible.
In addition to economic projections, accurate costing of fusion power plants is needed in order to determine whether or not the cost goals can be met. Attention has been focused on a comprehensive review and updating, as necessary, of specific unit costs and models used in the Demo Systems Code (DSC). Use of Level of Safety Assurance (LSA) cost credits is under review as it relates to distinctions between nuclear-safety-grade ("N-stamped") versus conventional unit costs and labor rates.
B. Safety and Licensing
The greatest promise of fusion is its potential for enhanced safety and environmental features. In addition to public acceptance and support, this feature can be translated into ease of licensing and waste disposal which would have a major impact on the cost of the power plant. These points have been strongly emphasized by our Utility Advisory Committee and subsequently reflected in the Demo goals and requirements.
A review of licensing procedures has been undertaken in coordination with the Fusion Safety Steering Committee in order to provide a sensible licensing scenario for the fusion Demo and power plants . Information and necessary guidelines for the licensing of fusion demo and power plants were provided by the Starlite Team. By nature, this a long term task and should be continued beyond this initial phase.
In addition to the efforts to develop appropriate licensing procedures, hazards assessments are being performed for selected critical safety concerns. For example, the U.S. stands alone in the world in its strong advocacy of liquid lithium as a coolant and breeder, which offers the promise of very high performance and simplicity which is expected to lead to enhanced reliability. The chemical reactivity of lithium has given other programs reason to rule out lithium a priori as an acceptable candidate. While measures have been proposed for minimizing the hazards , more extensive hazards analysis may be needed on specific designs in order to demonstrate its acceptability.
Reliability goals for a commercial reactor appear extremely challenging to meet. The systems are very complex, the operating environment for in-vessel components is extremely harsh (e.g., high heat flux, direct plasma exposure, high energy neutron bombardment, strong magnetic fields), and finally, the availability of test devices prior to Demo will be very limited due to the high cost of an ignited fusion plasma device. In order to meet the overall cost targets, an availability as high as 85% may be required, and certainly >75%. Given the current state of knowledge, there is no evidence to believe that this target can be met.
The RAMI data base for fusion is very limited, especially the data which is applicable to full-scale fusion power plants. There are several reasons for this situation. There are no operating fusion power plants or demos from which to obtain data. The data which is available from operating R&D facilities and experiments have not been systematically collected, organized, and analyzed. In any case, this data would have to be significantly extrapolated from present R&D experiments (which are scientific experiments and, by their nature, low availability) to operating power plants.
Some efforts have been undertaken previously to predict failure rates of individual components based on data from related technologies (see for example ). A more broad-based fusion-relevant RAMI data base is being initiated here by attempting to systematically collect data from operating fusion R&D facilities. By its nature, this task is long-term; continuous effort is needed to maintain and update the database and interpret the results. Engineering guidelines for improving RAMI numbers are an essential element and must be integrated into the design process.
The Starlite Project was initiated to investigate the mission, requirements and goals, features, and R&D needs of the Fusion Demonstration Power Plant. The Fusion Demo should demonstrate to utility customers and the general public that fusion power is a secure, safe, licensable, and environmentally attractive power source that is ready for commercialization at an economically superior total cost. To provide a basis for the design development, inputs from the end-users were solicited and analyzed to yield a Demo mission statement ans a set of top-level requirements. If this mission statement is achieved and the requirements fulfilled, the fusion Demo power plant should exhibit all of the attributes required for fusion to be a commercial success as a power plant heat source.
This work was supported by US DOE Contract DE-AC03-95ER-54299.
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