Experimental study of large scale axially heterogeneous LMFBR core at FCA, (6)

An experimental study for an axially heterogeneous LMFBR has been planned at FCA. Because enough plutonium fuel constructing a full mockup core of a large scale LMFBR are not prepared on FCA, axial and radial nuclear characteristics have been measured using the respective partial mockup cores in the program. Assembly XIII-1 is the standard core for measurements of nuclear characteristics in the radial direction. Assembly XIII-1 is a sector type core and has a test region simulated a core region of an axially heterogeneous LMFBR at the core center. The test region is surrounded by the driver region fueled an enriched uranium. Following nuclear characteristics have been measured (i) criticality, (ii) reaction rate and reaction rate ratios, (iii) power distributions, (iv) material sample worths and (v) B4C control rod worths in the experiment. In order to examine data and method for the calculation of nuclear characteristics of the axially heterogeneous core, the analyses have been made using cross section library JENDL-2 and JAERI's standard calculation system for a nuclear characteristic of a fast reactor. In the experiment, power flattening has been observed at the radial direction, which caused by neutron spectrum change due to exist the internal blanket. While the calculation have underestimated the fission reaction rates except U-238 in the internal blanket. (author)