Measurement method of relative burnup distribution of irradiated fuel

摘要

PURPOSE:To enable quick measurement in a shorter time than in the case of employment of a Ge semiconductor detector by determining the distribution of relative burnup of a fuel by the use of a large number of gamma-ray detectors disposed on the lateral sides of the fuel and by measuring the distribution therefrom. CONSTITUTION:When it is assumed that measurement of gross gamma-ray are executed at a plurality of points, a gross gamma-ray signal at an n-th measuring point is set as GGn, burnup at that point as BUn, a gross gamma-ray signal at a reference point as GGo and burnup at this point as BUo. From these values, the distributions gn=GGn/GGo and rn=BUn/BUo at the n-th measuring point are obtained. On the occasion, the burnup BUo is assumed to be known. By using an approximation formula, the distribution rn=gn.K (BUo, Tc)/K (Buo.gn, Tc) is led out. Tc is assumed to be a cooling period of a fuel. A factor expressed by a fraction in the right member of this formula represents a correction coefficient. The burnup distribution (rn) can be determined by substituting the distribution (gn), the burnup BUo and the cooling period Tc for a prescribed relation formula.