nd 2 IAEA TM on First Generation of Fusion Power Plants: Design and Technology 20-22 June, Vienna, Austria, 2007

SUMMARY

Under the topic of Power Plant Concept Analysis (PPCA) were presented eight papers. On his key note D. Maisonnier presented the development scenario for fusion in Europe based on a three step approach: i) ITER in validation of DEMO/reactor physics, ii) IFMIF for the qualification of materials for in-vessel components and iii) DEMO for qualification of components and processes of power plant operation. This approach constrained by budgetary considerations assumes as well success in the many different challenges ahead. Considerations were made for scenarios depending on the share of each step programme to the global goal and the necessary parallel supporting activities A detailed listing of objectives to be achieved before a power plant can be constructed was given and the time frame for these brings demonstration of electricity to the net by 2037. The author argued that a new approach could be considered to accelerate the fusion track at the cost of increasing the risk (challenges) and at the same time developing the programme with more conservative aims. A Enhanced (E)-DEMO pulsed device, water cooled and utilizing most of the ITER technology could start construction very soon and be a more stimulating goal, contributing to accelerate the power plant technology development. P. Sardin discussed alternative power conversion cycles to the Rankine cycle for Helium-cooled fusion reactor concepts. He proposed improvements of the gross efficiency considering other types of conversion cycles such as the indirect Brayton cycle using supercritical CO 2 as working fluid and the supercritical steam Rankine cycle, found to be the one leading to the highest efficiencies. In the later, the heat transfer is improved dividing the blanket helium heat exchange in two stages. The value obtained for “Cycle related Net Efficiency” (net power/reactor thermal power), 31.68%, represents a noticeable improvement compared to the one obtained for the sub-critical Rankine cycle of the reference model HCLL (Helium Cooled Lithium- Lead), which achieved a value of 28.34%. A 1-D reactor system analysis code has been presented by B.G. Hong. Developed at KAERI, the code finds the design parameters which satisfies the plasma physics and engineering constraints or optimizes the design depending on the given figure of merits. It includes a module to identify areas of further physics and technology development. It was utilized to investigate the performance of DEMO under three main requirements i) to demonstrate tritium self-sufficiency, ii) to generate net electricity, and iii) for steady-state operation. The results showed that to access the operation space for high performance the main restrictions are arisen from the divertor heat load and the steady-state operation requirements implying that developments in both plasma physics and technology are required to handle high heat load and to increase the current drive efficiency. The definition of development strategy, preliminary conceptual design and R&D, activities for a Chinese DEMO power plant was introduced by K.M. Feng. A fusion fuel breeder reactor concept requiring less demanding fusion technology was presented. The author gave a general picture of the development objectives for Chinese DEMO: continue the domestic plasma research effort using the experiments such as HL-2A ( HL-2M) and EAST, to strengthen the domestic fusion reactor research and to cooperate with international effort in DEMO design activities. R. Srinivasan presented the concept and results of a system code for fusion power plant conceptualisation. This code includes physics and engineering constraints and has been validated by applying it to existing tokamak devices. The base line design of Indian Fusion Power Plant (IFPP) has been constructed and also the requirements from various subsystems for this base line design have been identified. A conservative approach was taken with bootstrap fraction of 50%, safety factor about 3 (at 95%), Q=30 and input power 150 MW for a 3.3 GW fusion power. The elongation and triangularity are taken as 1.7 and 0.24 respectively and R/r ~ 3. For the blanket was considered of the Lead-Lithium Colled Breader type. In his paper, Norimatsu introduced a new concept of laser fusion. In this fast ignition scheme, a spherical hollow solid deuterium-tritium fuel is compressed to a high density of 1000 times solid density with tens of nano-second laser pulses from a compression laser. The compressed fuel core is directly heated to 5 keV with a ten of pico-second laser pulse from a heating laser. This FI scheme enables to design an IFE power plant with a 1MJ-class, compact laser whose output energy is 1/4 of previous central ignition scheme. Current computer simulations indicate that a thermonuclear gain of 160 will be achieved with 1.1 MJ / 10 ns compression lasers and a 100 kJ / 10 ps heating laser. El-Guebaly reported in detail on an optimised design for a fusion power plant based on the compact stellarator concept. This study developed in the US resulted in the ARIES-CS device concept with 7.75m average major radius similar to typical tokamak based design dimensions. A novel approach based on coupling the CAD model with the MCNP Monte Carlo code was developed to model the complex stellarator geometry for nuclear assessments. The most important engineering parameter that influences the machine size and cost is the minimum distance between the plasma boundary and mid-coil. Reduction on CoE by 30% and significant reduction of radwaste have been achieved in the present design when compared to previous ones. D.J. Ward presented a comparative analysis of different options for a European DEMO. He noted that DEMO is aimed to bridge the gap between ITER and a fully operating, high availability, power station. To assist on the concepts for DEMO, systems studies, using the PROCESS code, a wide set of options, covering a range of physics and technology choices were investigated. Detailed results for several concepts were presented for the divertor heat load indicating that with 3GW fusion power and 200MW heating power, the radiated power fraction should be above 60%. The study showed how coolant choice implies in the radial build depending if to use liquid or gas coolant. An important point is that operation without significant current drive forces the machine to be large with manageable divertor heat load as opposite to an increasing current drive power as the device size reduces but the divertor heat load increases. The study on the pulsed versus steady state showed that for the higher CD power cases the machines are smaller but that is not enough to guarantee lower costs. Three papers discussed the topic of Social, Economic, Safety and Environmental Aspects of Fusion. El-Guebaly presented a study on a new approach to manage fusion radwaste avoiding following the fission approach of geological disposal. Several aspects of handling the continual stream of fusion radwaste, replacing the disposal option with more environmentally attractive approaches, such as recycling and clearance were discussed. The speaker mentioned a few topics a requisites were more work is still required to allow a more efficient and attractive strategy such as: the notable discrepancies between the various clearance standards, the need for new clearance guidelines for fusion-specific radioisotopes, the availability of a commercial market for cleared materials, and the acceptability of the nuclear industry to recyclable materials. Young-Joon Choi presented the development of the Korean regulatory activities for fusion energy. A Strategic Technology Roadmap (STR) has been developed to establish the contents, schedule plan, and strategies in developing regulatory technologies. Thirteen technical areas such as materials, system design, accident analysis, and radiation assessment, etc. composed of thirty nine core regulatory technologies were identified in the STR. It is expected that these activities are supported by experience gained with the licensing of KSTAR and the experience gained in the participation on the ITER project. Application for licensing of Korean DEMO is expected to occur by 2020. In his paper, Zhi Chen presented a study for failure mode and effect analysis based on a bottom-up methodology for the Chinese ITER test blanked module design. For each component of the TBM, all the possible failure modes that could occur in the operating states were evaluated in terms of: accident frequencies and relative category classification, failure cause and possible action to prevent the failure, consequences, and actions to prevent or mitigate the impact of the resulting consequence. Twenty one incident initiators were identified covering malfunctions in the cooling circuit, loss of coolant, vacuum leaks, and specific component rupture. One example of application of this methodology was given for the case of loss of flow in a TBM cooling circuit due to circulator/pump seizure which will result in failure of several circuits and components which may lead to breaking of some of the TMB structures. There were four papers presented under the topic of Materials Analysis, Components Design, Plasma Requirements. C. Wong presented the study for a test blank module that in the US is expected to be very close to the requirements for a fusion power station. He generated DEMO parameters utilizing a system code and calibrating with ITER data. With the selection of ferritic steel as the structural material, the maximum neutron wall loading is limited to 3 MW/m2. A circa 2 GW fusion device with an aspect ratio of 2.6 was selected based on this assessment. For the ITER-TBM design the guidance is to apply a 2 mm Be layer onto the plasma facing surface but this would not perform well in a DEMO like reactor due to radiation damage. He analysed several possible first wall materials As boron or silicon have been used to condition all high performance tokamak experiments he proposed to use a new plasma facing component based on boron infiltrated in a W-mesh. This BW-mesh concept is at a very early stage of development and will be tested in DIII-D. Successful demonstration of in-situ boronization will have to be made. D. Filsinger gave an overview of the integration of the Helium Cooled Pebble Bed blanket into the reactor in which the ‘Multi-Module-Segment’ (MMS) concept is applied. The blanket modules are linked to the MMS by appropriately combining welded connections, flexible elements, and shear keys. The advantage is that this connection does not have to be handled inside the vessel. Besides, due to the integration concept this type of blanket attachment has to cope with only minor temperature differences between interfacing structural elements. In addition, electromagnetic loads are effectively compensated by this design. J. Karditsas presented an assessment on the criteria and implications for successful design, licensing and power plant operation. As currently, there are no established fusion specific licensing processes or component design codes any limits imposed on designs or performance were taken from existing design codes developed by the fission industry. He estimated that fatigue irradiation creep levels will be significantly higher for a fusion power plant that in fission. The models showed that high stress and low helium environments, as in fission, are less sensitive to helium embrittlement than low stress and high helium, as in fusion environments. In assessing the individual component analysis he stressed that the materials, properties, design curves, and all relevant design codes must be brought in-line with fusion neutron spectra and operating environment. Molten salt energy storage systems are well known and have been used in several industrial and domestic applications. Z. Homonnay presented a study for energy storage for re-initiating a pulsed fusion power plant with 4-8 h operation and dwell time of 5-20 min. The more promising option, he concludes, are the metal hydrides which have relatively high heat of fusion and, moreover, allow for combining heat of fusion with heat of a chemical reaction (where LiH is dissociated by the present of K and provides production of H2), thereby increasing thermal storage capacity. The latter offers controlled recovery of heat and even partial direct conversion of heat to electricity by thermally regenerative electrochemical cells. An economic analysis indicated that this method is expected to be competitive. Three papers where presented on the topic of Non-Electric Applications of Fusion. S. Konishi, looked at the future demand for energy and note that fusion must be attractive in many aspects to conquer the market share. Grid impact of a fusion plant under variable demand conditions may play a role on the acceptance. Besides this, fusion power plant will need something like 13% of auxiliary power to become exoenergetic. Projections show that the share of fusion seems to be higher in developing countries that are facing high grow rates on energy consumption as their smaller grids can still have some flexibility to be optimised to integrate fusion power plants. He also presented a study on the viability of utilizing a high temperature blanked for the first generation of fusion power plant. As the hydrogen marked is 3x higher than for electricity this co-generation approach would make fusion much more attractive. As for the fuel aspects e noted that fuel cycles, particularly lithium supply and tritium breading control will be also important. Public acceptance may be sensitive to the amount of radwaste that a particular technology for the blanket will generate. Mr. Liu presented the FDS-III fusion reactor concept for hydrogen co-production and preliminary results of this study. MHD calculations were used to set up the overall geometry with a target fusion power performance of ~2.5GW, neutron wall load of 3.5~4MW/m2 and the surface heat flux of ~0.8MW/m2. It is proposed an innovative high temperature liquid lithium–lead blanket concept based on the Reduced Activation Ferritic-Martensitic steel as structural material. The multi-layer flow channel inserts have been adopted in the LiPb channels to attain high outlet temperature, about 1000 C, to satisfy the need of high efficiency production of hydrogen. The blanket combines a banana shaped large module to improve maintenance efficiency and reduce effect of electromagnetic forces. A carbon dioxide Brayton cycle is used as it allows for best thermal efficiency. Preliminary cost analysis showed that the FDS-III is a competitive concept for fusion energy and hydrogen co-production. S. Wu presented, a concept of multi-function fusion reactor (MFFR) based on the existing fusion technology for exploiting the possibility of earlier application of fusion energy as volumetric neutron source. The 5.93 T, 2.5 GW reactor aims at different types of utilization such as fission waste disposal, plutonium 239 breeding from uranium 238, hydrogen producing, tritium producing, components test for fusion reactors and electricity power plant demonstration. Two fusion-driven sub-critical systems, the tokamak-based reactor and the spherical tokamak based compact reactor, have been investigated. He presented in detail the two major types of functional blankets selected for the MFFR. The sub-critical blanket mainly used for fission waste transmutation and the energy exchange blanket to produce hydrogen and for electricity power plant demonstration. He noted that the spherical tokamak-based reactor will be more attractive than the normal aspect ratio tokamak, if the technology problem of the central conductor is solved. Two presentations were given under the topic of Energy Policy, Strategy and Scenario for Fusion Development. I. Cook integrated the fusion development into a broader context, were present political decisions to mitigate climatic changes and public awareness are favourable to the fusion option. Recent decisions on ITER construction and on establishing the Broader Approach (BA) have made clear the near-future fusion steps. He defended that a sequential approach, risk conservative and constrained by funding, is not necessarily the fastest track, in particular given the high costs inherent to climate changes effects. Taking the projections for impact on climate changes it is absolutely needed to keep CO2 concentration below 550 ppm to avoid an average temperature increase of 3 C. Giving the present trends it seems justifiable and urgent to strengthen the fusion programme developing technology even if in a non-ideal form but faster, by relaxing the targets for the internal cost of electricity from the first generation of fusion power plants. Correspondingly reduced targets for the technical performance (e.g. plasma scenarios, materials endurance, blanket efficiency) of DEMO(s) aiming at demonstration of fusion electricity production in twenty years, may lead to widespread deployment of fusion power earlier than in previous fast track scenarios. Y. Wan noted that the projections for China economic growth, population increase and the demand in energy reaching 1.5 TW in 2050 would require a serious strategy on development of energy. The most promising path in satisfying this demand with reduced environment impact would be to increase the fissile power contribution (now only 1%) to 6% of the total capacity, duplicate the renewable contribution to achieve 30% of operating power plants and promote high efficiency coal power plants. Strong limitations on natural uranium ore would require breading of the fissile fuel and as well effective ways to manage and reduce by transmutation the radwaste. Therefore an aggressive fusion road map is being considered in China to accelerate fusion development. The targets are to achieve steady state operation on EAST in 10 years, contribute to the design, construction and assembly of ITER, and construct a first test multi- function fusion reactor by 2020-2030.