[en] Purpose: To make it possible to automatically carry out determination of the soundness of fuels by analyzing reactor water after sampling and further analyzing the result obtained, and to rapidly graph and display the result. Constitution: The iodine concentration of a sampled reactor water is measured by a concentration measuring device, and further the concentration of its absolute radioactivity is measured thereby. The measured and read out concentration of the reactor water is further classified into a recoil composition, a balance composition and a diffusion composition. A comparing device is to carry out determination of the soundness of fuels, and compares the quantity of the reactor water concentration, the quantities of the above described recoil, balance and diffusion compositions and their ratios with fuel failure pattern data stored beforehand thereby to determine to which fuel failure pattern stored beforehand the actually measured data belongs. On the basis of the result of determination, displays of the fuel conditions such as ''normal'', ''abnormal'', ''caution'' etc. are performed. Respective quantities of balance, recoil and diffusion compositions and the measured results (the iodine concentration in the reactor water) are graphed by the graphing device. (Yoshino, Y.)