Burnup degree measuring device

The device of the present invention comprises two detectors for measuring neutrons opposed to each other on both sides of a fuel to be tested, two counting means individually inputting output signals from the detectors and counting and accumulating them, a comparing and judging means for comparing the output signals from each of the counting means and judging the presence or absence of a difference exceeding a predetermined value in the counting and accumulation between them, two correction calculation means for correcting and calculating the distance between the fuel and each of the detectors caused by the positional displacement based on the output signals from the counting means and the output signals from the comparing and judging means, a calculation means for averaging the output signals from each of the correction and calculation means and a means for outputting the output signals from the calculation means. Correction calculation is performed for the non-linear characteristic by determining the distance based on characteristics determined previously by tests and each of the counting and calculating values of the two detectors, thereby enabling to measure an accurate and stable burnup degree even when positional displacement occurs between the fuel and the detectors. (N.H.)