Abstract: A subchannel analysis code THAS--PC2 running on a microcomputer is developed to computethe flow, temperature and pressure distributions in fast reactor fuel assembly for both steady stateand transient conditions. The steady state and transient calculations of the fuel assembly for the Experimental Fast Re-actor are made on a microcomputer by use of THAS--PC2 code. The calculated results for thesteady state are as follows: average core exit temperature and temperature rise are 557℃ and157℃ respectively, maximum cladding surface temperature and maximum fuel center temperatureare 601℃ and 2410℃ respectively, which occur all on the central fuel pin. The maximum coolanttemperature is 593℃. The loss of primary pump power accident (secondary scram) is chosen forthe transient calculation. The calculated maximum coolant temperature and maximum claddingsurface temperature are 630℃ and 637℃ respectively when t = 2s. They are far lower than boil-ing point of sodium and safety limit value.