Study on thermal expansion reactivity of CEFR control rod drive mechanism

During the power test phase of CEFR, the power reactivity measurement test was carried out. The results showed that there was a large deviation between the theoretical calculation and the experimental measurement. It is necessary to analyze the causes of deviation and correct it. The main reason for the deviation is thermal expansion. As the sodium temperature rises, thermal expansion occurs in the control rod drive mechanism, main vessel, core, distribution header, moving component and absorber in the control rod. The relative displacement causes the control rod shift downwards and insert negative reactivity. This paper calculates the thermal expansion of each part and corrects the theoretical calculation. The theoretical calculated of power reactivity is −486pcm, and the total reactivity obtained by theoretical calculation and correction is −943.43pcm. The results show that the relative deviation be-tween theoretical and experimental reactivity decreased from 54.83 % to 12.32 %.