1 Three confinement systems - Spherical Tokamak, Standard Tokamak and Stellarator: A comparison of key component cost elements T. G. Brown Abstract— Since the 1950’s “Next Step” fusion devices and to promote a viable maintenance strategy but rather a physics power plant studies have been developed for a number of mag- device to demonstrate conditions of a burning plasma. netic confinement systems but an open question remains…can a Concept designs for a planned DEMO project will need to magnetic fusion device be simplified to the point where it will be cost competitive and operate with high availability? Concept couple physics operations with design strategies that empha- designs based on the ARIES advanced tokamak (AT), spherical size effective maintenance schemes and component details tokamak (ST) and the quasi-axisymmetric stellarator (QAS) with attention given to reliability practices that foster high option have progressed in recent years through a series of PPPL availability operations. Configuration influences need to extend studies with an underlying intent to improve the engineering beyond the device core itself and include interaction of aux- feasibility of each, giving special attention to concepts that sim- plify the device configuration and improve maintenance features. iliary equipment and services as well as addressing strategies For the spherical tokamak option, design details centered on a to reduce the size of any external maintenance and storage 3m Fusion Nuclear Science Facility that evolved to incorporate facility. Fusion is years away from the construction of a vertical maintenance, HTS magnets, a small inboard DCLL DEMO plant and although physics feasibility is needed to blanket and a liquid metal divertor. In collaboration with the underpin its viability, engineering and economics will play K-DEMO and CFETR concept study teams the tokamak design has evolved to increase plasma component access within a vertical a major role in deciding the success or failure of DEMO and maintenance approach using enlarged TF coils incorporating a fusion itself. low and high-field Nb3 Sn winding pack that provide a peak field It’s often thought that at this stage of development one of 16T. A recent PPPL stellarator study focused on simplifying cannot define the cost of a fusion power plant. But maybe you the stellarator winding topology to improve access to in-vessel can and maybe defining a target cost can help move the design components; combining coil optimization with winding surfaces that incorporated geometry constraints specified by engineering. process toward a credible economical outcome. A fusion This study centered on a 1000 MW power plant design with a power plant will be capital intensive and in all likelihood tokamak like vertical maintenance scheme that allows access to follow a path similar to the design and construction of a remove large internal blanket sectors. nuclear fission plant. The construction cost estimates for new Results of three confinement studies (PPPL developed ST, nuclear power plants are very uncertain and have increased K-DEMO and the PPPL developed QAS stellarator) will be presented to highlight concepts that simplify each device config- significantly in the past decade. Global nuclear power has uration and improved their maintenance features. Scaling each stagnated and is in total decline in the U.S., especially since the option to a common 1000 MW net electric power plant mission Fukushima disaster. Early 2008 data show new nuclear units allows comparisons to be made of key cost elements such as are planned were in the total cost range (including escalation the size of major core components, sizing of the reactor hall or and financing costs) between $6 billion and $9 billion for external facilities needed to handle and store activated in-vessel components. each 1,100 MW [1]. The U.S. Southern company, Georgia Power was building two AP1000 1,100 MW reactors at the Index Terms — in-vessel arrangement, maintenance approach, Vogtle nuclear power station at a cost of $7.4 billion each; reduced part count, simplifying feature unfortunately, the project is now on hold pending outcome from Toshiba’s Westinghouse unit who filed for bankruptcy in I. INTRODUCTION wake of billions of dollars in cost overruns at two U.S. nuclear power plants it is building in the U.S. Southeast [Reuters]. USION experimental devices have evolved in efforts to The fusion process is more complex than fission implying Funderstand plasma operating conditions and now through that a fusion power plant will expected to see higher capital the ITER project will make the long-awaited transition from and operating costs. Fusion does offers safe operation without experimental studies to burning plasma physics conditions, a the possibility of a meltdown and although it produces radioac- critical step in the path to a full-scale electricity-producing tive waste the waste generated last a much shorter time period fusion power plant. The ITER tokamak design is an outgrowth – all of which can be considered a value-added enhancement of the EU JET physics device and is not a machine designed over the cost of a fission power plant. This value-added enhancement of fusion can be used to increase the capital “Research supported by the U.S. Department of Energy under Contract No. cost of a fusion plant relative to fission…to some limit. If one DE-AC02-09CH11466 with Princeton University.” Thomas G. Brown, Princeton Plasma Physics Laboratory, Princeton, NJ were to assume the intrinsic value of fusions enhancement 08543 USA (email: [email protected]) was a 25% premium over the capital cost of a fission plant, Digital Object Identifier: 10.1109/TPS.2018.2832457 1939-9375 c 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information. 2 it would imply a fusion plant could be economically viable II. LESSONS LEARNED FROM THE CONSTRUCTION OF if its capital cost did not exceed $7.5 - $11.25 billion. Is NUCLEAR FISSION POWER PLANTS the intrinsic value of fusions enhancements worth more than Building a nuclear power plant has had its challenges 25%? Is the intrinsic value of fusions safety enhancements in recent years with large companies experiencing financial worth less than 25%? If improved safety and waste conditions losses, plants under construction behind schedule where the of fusion offers little intrinsic value then the economics for high cost of delays make the nuclear plant less competitive fusions looks to be dire. If the safety and waste conditions are with respect to alternate energy sources [2]. Not all organiza- noteworthy but the fusion plant electricity production per year tions or countries have undergone the same set of construction is significantly less than a fission plant due to low availability difficulties. South Korea and China both keep nuclear build- then any intrinsic value that might exist will be marginalized. ing costs low through repetition and standardization. Korean There is an upper cost limit above which makes any power power plant capital costs have remained fairly stable the past plant economically impractical. Nuclear plants get built by 20 years, while they have tripled in France and America [3]. large companies with huge assistance from governments in Because of frequent cost overruns in large power plants there the form of loan guarantees. It’s difficult to obtain funding for is an interest in developing small modular reactors (SMR). very high fixed cost projects that have a history of cost risk and NuScale Power has developed an SMR design that has been long horizons for repayment. If something goes wrong with submitted to the U.S. Nuclear Regulatory Commission for a the project, all up-front money is lost. Rapid advancement in planned construction on the site of Idaho National Laboratory competing technologies is also a risk for nuclear power. Solar in the U.S. [4]. A NuScale SMR unit is designed to delivers power is becoming cheaper and energy storage research is about 50 MW with twelve operating together to create a 600 advancing which places pressure on the economics of nuclear MW power plant. A key safety feature of NuScale’s SMR power. Given the finance history in raising large upfront design is that the small size, with large surface-area-to-volume finance capital for nuclear fission power plants and advances ratio, prevents any kind of meltdown. Westinghouse has a in competing technologies, it seems unreasonable to assume SMR design incorporating passive shut-down safety features fusions operation enhancements will offer high intrinsic value; that provide 225 MW [5][6]. therefore a 25% markup appears to be a generous upper bound Some of the leading conditions contributing to rising fission for this estimate. Given this assessment a fusion power plant power plant costs has been contributed to lack of standardiza- constructed in the U.S. might be valued between $7.5B and tion, increase in the complexity of power plants, safety related $11.25B; lower values are possible in countries where lower regulatory interventions and construction delays [1][7][8][9]. construction costs are prevalent. Another question to asked – Advanced construction methods have been used to reduce can a fusion power plant based on any confinement option nuclear power construction costs by shortening the time being considered be constructed within this price range and needed to build a plant. One major take-away involving con- eventually operate at a high availability as an operational struction improvements is that improved construction methods fission power plant? must be made in the conceptual design stage and then followed Knowing design and construction conditions that can cause through consistently throughout the project design phase; a cost overruns in fission power plants can be useful in defining statement that needs to be taken seriously and imbedded design conditions or economic factors that can also impact the early in the fusion DEMO design process.