The coated particle fuel has been developed within a framework of the HTTR (High Temperature engineering Test Reactor) Development Program at the Japan Atomic Energy Research Institute. The HTTR fuel is a prismatic block type containing TRISO-coated UOz particles. Research and development on the fuel has been progressed in three categories; a work for fuel production technology, a proof test of fuel performance and a safety-related research. In the present report the concept and outline of the fuel in the HTTR design are firstly described, and then fuel fabrication technology including recently developed methods for improving fuel quality is followed. Tests for proving fuel performance have been carried out extensively on the reference fuel of the HTTR design by irradiation in an in-pile gas loop and capsules, and typical results are presented in this report. Concerning the safety-related research, fuel failure and 137 Cs release at abnormally high temperature are described.

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T h e spent fuels from the JPDR-I reactor were measured by means of a 7-scanning facility installed in t h e fuel storage pool.T h e spatial distributions of the fission products (larCs and lSiCs) were measured and analyzed in reference t o the effects of control rod pcttern. T h e ratios holding between t h e products of neutron capture and of direct fission (1a4Cs/13iCs and 16rE~/1S7Cs) were also examined for i t s relevance t o non-destructive burnup determination. T h e activity ratios of the fission products can be expressed by a linear function of burnup, provided that corrections a r e made t o account f o r differences in irradiation history and for spatial variations in t h e neutron spectrum.

Precise measurements of burnup and accumulated transuranium elements were carried out on specimens which were taken out from spent fuel of Japan Power Demonstration Reactor (JPDR) -I, by means of chemical analysis and r-ray spectrometry. Results of the measurements are summarized numerically. Core configuration and operational history of the reactor are also described.

T h e spent fuels from the JPDR-I reactor were measured by means of a 7-scanning facility installed in t h e fuel storage pool.T h e spatial distributions of the fission products (larCs and lSiCs) were measured and analyzed in reference t o the effects of control rod pcttern. T h e ratios holding between t h e products of neutron capture and of direct fission (1a4Cs/13iCs and 16rE~/1S7Cs) were also examined for i t s relevance t o non-destructive burnup determination. T h e activity ratios of the fission products can be expressed by a linear function of burnup, provided that corrections a r e made t o account f o r differences in irradiation history and for spatial variations in t h e neutron spectrum.