Report on result of special test of fast experimental reactor "JOYO"; Isothermal reactivity coefficient and flow rate reactivity coefficient

not registered; not registered; Yamanouchi, Sadamu; not registered; Enokido, Yuji*; Shibahara, Itaru*; not registered

The isothermal reactivity coefficient and the flow rate reactivity coefficient of the Fast Breeder Reactor "JOYO" were measured during the power ascension test of 50MW. After 4 years operation, the core configuration of "JOYO" was increased to 79 from 70 subassemblies. The present experiment was intended to search the age effect for the above reactivity coefficients. The results obtained were as follows. [Isothermal reactivity coefficient] (1)The present value measured ((-3.850.17)10% k/k/C) shows good agreement with the design value and the value measured previously. (2)The age effect and the effect caused by the anomaly of the power reactivity coefficient are not found. [Coolant flow rate reactivity coefficient] (1)The reactivity change caused by changing of the flow rates in primary sodium loop (100% to 20%) was (-8.2-10.7) 10%k/k. This value is about 1/10 of the design value and 1/3 of the measured value before the 75 MW power ascension test. (2)The detailed analysis is needed to search the relation between the anomaly of the power reactivity coefficient and the above change of this coefficient.