A conceptual design is presented for the I/S process for the production of hydrogen using a high-temperature nuclear heat source to split water. The process includes a countercurrent reactor being developed by CEA within them framework of an international collaboration (I-NERI project) with DOE at General Atomics (San Diego, CA). A ProsimPlus (TM) model of the flowsheet indicates 600 kJ high-temperature heat and 69 kJ electric power are consumed per mole of H(2) product (with an assumed pressure of 120 bars). The net thermal efficiency would be 38% (HHV basis) if electric power is available at a conversion efficiency of 45%. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.