H igh Temperature Reactor Reactor coolant (RTT) is one of the Generation IV reactors are designed with the concept of co-generation plant for power generation and steamproduction that can be used as hydrogen production, desalination of sea water and other chemical production processes. FIT in addition to the successful design is determined by the performance of the IHX is also determined by use of heat which is used in cogeneration systems with heat exchanger rekuperator (Secondary Heat Exchanger,SHX).Rekuperator performance parameters are affected by the effectiveness (efficiency) and the configuration of the cogeneration system SHX in High Temperature Reactor (RTT). Modeling calculation of the effectiveness and value of LMTD heat exchanger SHX done with a heat transfer model calculations. Resulting from the calculations that for theGT-HTR300C, has a value of 65% and the effectiveness of its LMTD for 37.46 °C on the condition of Ts, and Ts in, out at a temperature of 900 °C and 500 °C, and Tt, in and Tt, out at a temperature of 280 C and 560°C and will produce maximum steam production of 37.46 kg / s; For GT-MHR300C, has a value of 54% effectiveness and its LMTD for 10.84 °C on the condition of Ts, and Ts in, out at a temperature of 925 °C and 565 °C, and Tt, inand Tt, out at a temperature of 260 °C and 580 °C and will result in the production of steam at a maximum of 105.77 kg / s; For ANTARES, has the effectiveness of 65% and LMTD was at 105.89 °C on the condition of Ts, in and Ts, out at a temperature of 875 °C and 475 °C, and Tt, in and Tt, out at a temperature of 260 °C and 580 °C and will result inthe production of steam at a maximum of 105 , 89 kg / s.