The accident of Chernobyl's nuclear power plant

The Soviet Union announced six major improvement measures for preventing another accident of the RBMK type nuclear reactor. The present study is aimed at technical evaluation of these measures. The structure, performances, nuclear-heat hydraulic power characteristics (coolant void coefficient, dynamic characteristic parameters, graphite exothermic reaction, etc.) of the Chernobyl's nuclear reactor are examined to determine the plant behaviors from 1 : 19 on April 26 until the accident and after 1 : 23 : 04. By using the FATRAC code and the EUREKA-2 code, which have been proposed previously, analysis is made of the changes in neutron flux, recirculation flow rate, steam separator pressure, water supply rate and steam separator water level for the period before the accident, and changes in thermal output, overall reactivity, void reactivity, Doppler reactivity and control reactivity for the period after the accident. Results show that the two codes can reproduce the values announced by the Soviet Union. Detaled analysis is also made for the above-mentioned parameters after the accident under various assumed conditions. Based on these analyses, some measures are proposed to effectively prevent serious damage under the same accident conditions as experienced in Chernobyl. (Nogami, K.)