The high-temperature gas-cooled nuclear reactor (HTGR) is an attractive potential source of primary energy for many industrial and chemical process applications. The HT^R core designs which have been developed for electric power generation using the Rankine cycle operate at relatively low exit gas temperatures, 1033 K (1400°F). Depending on the chemical process, reactor exit gas temperatures up to 1477 K (2200°F) may be required for the nuclear process heat system. Significant modification of

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... rrent HTGR core design will be required to achieve the required elevations in exit gas temperatures without exceeding the maximum allowable temperature limits for the fuel material. A preliminary evaluation of the effects of various proposed design modifications by predicting the resulting fuel and gas temperatures with computer calculational modeling techniques is reported. The design modifications evaluated are generally those proposed by the General Atomic Company (GAC), a manufacturer of HTGRs, and some developed at the LASL. The GAC modifications do result in predicted fuel and exit gas temperatures which meet the proposed design objectives. Future additional effort is indicated which should deal with alternative designs differing significantly from the design studied, and should include an evaluation of their relative resistance to possible accident conditions or off-design operation. I.