Report of the 1992 EPRI Fusion Panel Robert L. Hirsch, Chairman Floyd Culler Nari G. Hingorani John J. Taylor Thomas R. Schneider Dwain F. Spencer Background Fusion is one of only a few very long-term (multi-century) options for the central station generation of electric power. As such, an informed awareness of the status of fusion development is important to the electric utilities and to EPRI. In its recent "National Energy Strategy" report, the U.S. Department of Energy states that it intends to carry out a goal-oriented fusion development strategy, with the aim of operating a demonstration plant by about 2025 and a commercial power plant by about 2040. Around the time the DOE was preparing this strategy, budget pressures caused them to narrow their civilian development program to the Tokamak magnetic confinement concept. A significant research program on inertial confinement fusion is maintained primarily for defense purposes but with possible civilian application also. Many in the utility and engineering communities have raised questions about the suitability of both the Tokamak and inertial confinement as commercial power sources, while recognizing their unquestioned pre-eminence in achieving fusion plasma conditions. These questions, coupled with a possible interest in becoming more involved in the development of fusion power, led EPRI senior management to establish a panel of senior executives to consider a wide range of conceivable fusion reactor opportunities. Purposes of the Power Review The purposes of the 1992 EPRI Fusion Study were as follows: 1. To evaluate a wide range of fusion concepts from a utility desirability standpoint. 2. To enhance EPRI's perspective in fusion. 3. To provide guidance to DOE on fusion concept characteristics important to utilities. 4. To provide a basis for re-establishing DOE-EPRI communication and cooperation 1992 EPRI Fusion Panel In the end, time constraints did not allow closure by the panel on Item 1, although the panel was able to distill from its review a number of general characteristics that a commercial fusion power plant should strive to incorporate. The Review Process The Panel met twice. At the first meeting, June 1-2, the Panel received broad overview presentations on fusion reactor design principles from Prof. Gerald Kulcinski of the University of Wisconsin and the range of fusion concepts from Dr. Stephen O. Dean of Fusion Power Associates. At the meeting, the Panel discussed and established operational considerations that would be used to judge the desirability of the fusion concepts from a utility perspective. These considerations subsequently were provided to speakers prior to the second planning. The second meeting of the Panel took place July 6–8. At that meeting, the designs for three classes of possible fusion reactors were presented in the categories of magnetic confinement, inertial confinement, and colliding beams. A total of 13 specific concepts within these three categories were described by expert advocates. A listing of the presentations is given in Appendix A. At the end of the July 6-8 meeting, the Panel formulated its conclusions and recommendations. The Fusion Concepts In order to carry out this review, it was decided to assume 1) favorable physics performance and 2) adequate economics in order to focus on the engineering characteristics of the various concepts. The rationale for these ground rules was that neither the physics nor the basic economics could be established clearly in all cases at this time. In fact, favorable physics, engineering, and economics all will be required in a successful fusion reactor, and, of course, all three characteristics will be interrelated in differing ways. Magnetic confinement fusion concepts fall into two general categories. The first consists of relatively large devices with large, high field superconducting magnets. The mainline Tokamak and the Stellarator are examples of this type. The primary engineering problems requiring attention for these concepts are materials lifetime, ash removal and impurity control, and maintenance procedures. The Tokamak also faces issues related to elimination or control of plasma disruptions and the demonstration of efficient steady state current-drive technology. The second category of magnetic concept, called "compact concepts," have higher power density in the plasma core, which may lead to more favorable economics but can exacerbate materials lifetime problems. However, several of the compact concepts have simpler mechanical configurations, easing maintenance. The magnets for the compact concepts tend to be smaller and/or lower field strength. Because these have received less attention 1992 EPRI Fusion Panel than Tokamaks and Stellarators, their technical uncertainties are greater. Within this type, the Field Reversed Configuration and the Spheromak have especially interesting reactor configurations. The inertial confinement fusion concepts all have similar central core configurations. They conceivably could be powered by a variety of laser or ion beam "drivers" to produce the required microexplosions for power production. The use of renewable chamber walls could greatly ease materials lifetime problems, although the problem of transporting the beams and pellets into the chamber several times per second will require considerable engineering development. Development of cost effective, low-maintenance driver technologies is another development challenge. The possibility of "driving" more than one reactor chamber from a single driver and the prospects of varying reactor output by varying pulse repetition rate are interesting features of the inertial fusion concepts. The colliding beam designs have received the least attention but have some potentially attractive features, which appear increasingly more desirable as our knowledge of fusion reactors advances. This approach appears to have fewer "high tech" components and simpler overall geometries. Also, these concepts are more compatible with the use of fusion fuel cycles with fewer and lower energy neutrons, thus easing the materials lifetime problems. Operational Considerations The Panel developed a set of operational considerations to be used in assessing fusion concepts from the point of view of their desirability to an electric utility. These represented certain compromises that were believed necessary to accommodate to the current state of fusion energy development. These criteria were as follows: Complexity of the reactor configuration. Fusion reactors are likely to be more complex than today's power plants. However, within the range of possible fusion concepts, some appear to be more complex than others. Simplification is fundamental to many aspects of reactor desirability and can provide directions for improvement/invention in a given concept area. • Aspects of a configuration that can limit plant availability, including component lifetimes. Power plants must operate with high availability in order to meet demands at low costs. Concepts that require frequent replacement of components, requiring timeconsuming maintenance procedures, will be affected adversely. Frequent first wall replacement requiring long down times is a special problem of this type for a number of fusion concepts. • Fuel choice and cycle. Most fusion researchers have chosen the deuterium-tritium fuel cycle because of the relative ease of reaching required fusion plasma conditions, a key initial goal of the federal program. However, this cycle has the disadvantage of * * 1992 EPRI Fusion Panel releasing most of its energy in the form of 14 MeV neutrons, which create severe materials damage. Also, this cycle requires a complex tritium breeding sub-system and does not lend itself readily to advanced energy conversion techniques that substantially could improve overall power plant efficiency. Energy balance, including subsystem efficiencies. Some fusion concepts are inherently steady-state, with ignited plasmas and low recirculating power, while others are pulsed repetitively on various time scales or are "driven," thereby requiring higher recirculating power, which can reduce overall plant efficiency. Safety. Some concepts have smaller "energy reservoirs" that could be released during accident conditions. Concepts with lower radioactive inventories will have a relative advantage. • Waste. The volume and character of radioactive materials requiring periodic removal and storage must be minimized. • Siting. Systems that require unusually large land areas or complex licensing challenges will have more difficult siting problems, which would be less desirable. • Technical uncertainties. Concepts about which less is known frequently appear more desirable at an early stage of development. Their desirability must be somewhatdowngraded because reality usually turns out to be more complex. The above were judged by the Panel to be the major operational considerations for fusion concept comparison and evaluation. In addition, the following characteristics were deemed to be important as further differentiators: Range of possible plant sizes (MWe). Smaller, possibly modular, systems could require lower development costs and risks and have the potential for more rapid development. • Fuel Cycle flexibility. Concepts that appear capable of accommodating different fuel choices/cycles or to produce other than electricity could be more desirable than concepts that are more limited. • Power density. While higher power density can lead to smaller systems with potentially more attractive economics, other engineering issues can complicate matters. Thus, power density alone is not a simple measure of desirability. • Power conversion. More efficient systems and concepts that allow use of advanced power conversion technologies are usually more desirable. • Development schedule. Concepts that permit a development path based on smaller 1992 EPRI Fusion Panel Conclusions and Recommendations 1. The federal fusion research program represents an important national investment. 2. In the relative near-term, producing deuterium-tritium fusion power in the 10–20 megawatt-thermal range in the Princeton TFTR is an important program milestone and should continue to be a high priority. 3. Because commercialization is a long way off and this field of technology is highly complex, there are significant tradeoffs to be made. Accordingly, program diversity beyond Tokamaks is important. 4. In diversifying its fusion program, DOE should give special consideration to the following: -Concepts and/or designs that may be less complex. - Power plant designs without tritium burning, because of the very serious materials problems associated with 14 meV neutrons. - Use of certain low activation materials. - High overall energy conversion efficiency, e.g., combined direct electrical and thermal conversion. -The outage and waste disposal problems of changing out large volumes of fusion reactor core materials every few years. - The importance of effective ash removal from fusion plasmas. 5. Engineering thinking and the eventual needs of the marketplace should become a critical element in fusion program planning and decision-making. 6. The basic goals of the EPRI Fusion Panel remains worthwhile, namely for a qualified group of utility-oriented engineers to evaluate the various fusion concepts from the point of view of their ultimate use in electrical power production. The EPRI panel experience indicates that such an evaluation will require more time and effort, if it is to be done properly. The DOE may wish to consider initiating such a study under its own aegis, possibly in conjunction with EPRI. 7. EPRI should become involved in fusion R&D at a modest level, preferably through the Exploratory Research program. |