High-temperature gas cooled reactor HTTR reaching the first critical point

Outline, fueling, conditions of criticality test, and future plan of HTTR (high-temperature test reactor) of Japan Atomic Energy Research Institute are described. HTTR is the world first nuclear reactor that can directly take out high-temperature helium gas of 850-950degC outside the reactor pressure vessel, and aims at establishment and upgrading of high-temperature gas cooled reactor technological basis and frontier basic research of high-temperature engineering, and started the construction in March 1991 and reached the first critical point on November 10, 1998. The basic specifications are: Output: 30 MW; primary coolant: helium; core material: graphite; core height: 2.9 m; core diameter: 2.3 m; fuel: uranium dioxide coated particle/graphite dispersion-type; uranium enrichment: 3-10% (average 6%). The enrichment can be adjusted by site so that temperatures of the helium flowing out are uniformly distributed. The critical point was reached with 19 fuel columns filled out of full 30 columns and with 16 pairs of control rods all drawn out except the central control rod, which was gradually drawn out to about 60% of the stroke. Then, fueling proceeded to the full 30 columns through 21, 24 and 27 for further nuclear characteristic tests. The full output is planned to reach in a year from the start of the output increasing test in September 1999. (M.M.)