A. Sagara

A. Shimizu

S. Ebara

T. Yokomine

National Institute for Fusion Science (NIFS-Repository)

Tor h Pr.C.I.e. III.e. IHowever, the problems related to the concept becamealso clear through the examination. Although the relativepressure drop through the cycle path was fixed at 0.1 whichwas the typical value in conventional gas turbine cycles, thepresent cycle contains total 7 heat exchangers in theoperating flow path so that it cannot be applied as it is andthe pressure drop reduction in heat exchangers is the key.Overcoming the leakage of tritium containing helium gasthrough shaft bearings is also important.5. PerspectiveMany problems are remained to be solved beforerealizing the gas-turbine systems in nuclear energyapplication both in fission and fusion fields. However,several important activities are now being performed. Forinstance, the R&D activity is being made to realize highlyefficient heat exchangers by combined team of JAERI andMitsubishi Heavy Industry Co. for HTGR power cycles, inwhich a plate-type ultra-fine fin heat exchanger is reportedto be able to achieve over 95% heat exchange efficiency.Moreover, the new concept of ultra-high temperaturegas-cooled fission reactor is now examined in whichSiC-SiC composit is considered to be the main structuralmaterial, which will contribute much for the breakthrough ofupper temperature limit. These activities will accelerate. thesolution of the problems related to the closed hehumgas-turbine cycles.ReferenceThe Design of High Efficiency Turbomachinery and GasTurbines;D.G.Wilson & T. Korakianitis, Prentice Hall,1998........IL..L..I. : l i J J .§ 5. Possibility of Gas-Turbine EnergyConversion System for FFHR's LiquidBlanketShimizu, A., Yokomine, T., Ebara, S. (InterdisciplinaryGraduate School of Eng. Sci., Kyushu Univ.),Sagara, A.1. Gas-turbine systems for liquid blanket of FFHRIn spite of its long research history and its possibility ofrealizing high energy conversion efficiency, the gas-turbinesystem has not yet beem realized in the field of nuclearenergy. In the fission field, the gas-cooling hasdisadvantages to the light water cooling in that its poor heattransfer performance limits the volumetric power generationrate and the coolant outlet temperature itself is restricted to arelatively low level due to the requirement of forming aperfect fission product barrier to the environment. .On the other hand, a liquid blanket concept is now bemgexamined in the design study of FFHR, wherein molten saltFLIBE is assumed to be a coolant that serves as tritiumbreeding material as well. Combination of the FLIBEcoolant and some advanced structural materials such asferritic steel or vanadium alloy has a latent possibility ofconstructing safe and economical system with less pumpingpower. In this concept, the thermal energy outputtransported by the FLIBE should be transferred to a certainpower cycle via. a heat exchanger. Of several candidatecycles, that of helium gas-turbine is attractive from itsinherent safety and also from the possibility of tritiumhandling in dry conditions. When usual light water Rankinecycle is adopted, recovery of permeated tritium from thepower cycle circuit will be very difficult.2. Multi-stage compression/expansion gas-turbineMeanwhile, the operating temperature region of FLIBE isextremely restricted due to its corrosive character as well asdue to the high temperature creap of the structural materials,the upper and lower temperature limits being 550°C and450°C, respectively. In order to realize an efficient gasturbine cycle that uses such low and limited heat receivingtemperature, an adoption of multi-stage compression andexpansion cycle that changes the cycle pattern from aslender shape to the Carnot one on TS or HS diagram isinevitable.3. Energy conversion efficiencyWith this background, the energy conversion efficiencyof a closed helium gas turbine cycle was estimated, theattention being fixed on three-stage compression/expansiongas-turbine cycle. It consists of one pre-cooler, twointer-coolers, one regenerative heat exchanger, one mainheat exchanger, two reheaters as well as three compressorsand expanders. Heat rejecting temperature was fixed at30°C and the compression and expansion ratio for each threestages was assumed to be of equal value.According to the estimation, the maximum cycleefficiency of 37% was found to be realized when the stagecompression ratio was 1.5, which can be favorablycompared with standard thermal efficiency of conventionalnuclear power plants.4. Problems to be overcome247

Possibility of Gas-Turbine Energy Conversion System for FFHR\u27s Liquid Blanket

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