Experimental and computational study of power distribution flattening in a reactor of GT-MHR type at 'ASTRA' critical facility

The paper presents the results of experimental and computational study of flattening the spatial distribution of 235U fission reaction rate in a critical assembly ASTRA with the annular core and poison profiling elements placed in the inner graphite reflector near the boundary with core. Presented computational analysis of experimental data was performed with the set of codes used in HTGR design calculations. It was shown, that the power distribution flattening (235U fission reaction rate) in an annular core of a modular reactor such as GT-MHR could be achieved, in the certain degree, by the inserting the poison profiling elements in the inner reflector near the boundary with the core. The analysis of divergences of computational and experimental values of the 235U fission reaction rate shown that the maximal deviations lay in a range of 5-7 % excepting two points in the inner reflector for the 1A configuration, where value of deviation reaches 8 %. It should be noted that the error of the experiment does not exceed 5 %, so the calculational values only slightly exceed an experimental error. (authors)