Experimental study of power distribution in FCA XV cores with half-inserted B4C control rod

Axial and radial power distributions were measured in FCA XV-1 and XV-2(95V) cores with half-inserted B4C control rod to improve the calculational accuracy of reactivity worth of B4C control rod. FCA XV-1 core has a zone type test region simulating a plutonium fueled HCLWR and XV-2(95V) core simulated a 95% voided state of coolant in HCLWR. Experimental results showed that reactivity worth and power depression by B4C control rod were closely related and there was a nearly linear relation between them in the range of present measurement. Therefore, the calculation which gives an accurate power depression was considered to give an accurate reactivity worth. The calculation using JENDL-2 and SRAC gave smaller reactivity worth and power depression than the experiment. The homogenization effect in cell calculation was considered as one of main causes of these underestimation and estimated to be about 5%. (author)