A new method of nondestructive measurement for assessment of material degradation of aged reactor pressure vessels

A method, MIM (magnetic interrogation method), is proposed for nondestructive measurement of radiation damage of nuclear reactor pressure vessels. The method relies on good correlation between the levels of radiation-induced hardness change and magnetic coercivity change in pressure vessel steel. A part of the pressure vessel to be inspected is magnetized with two-pole magnetic yokes through the overlay clad of nonmagnetic stainless steel, and magnetic field distributions on the surface of overlay clad are measured in the vicinity of the poles of magnetic yokes. Then, the coercivity distribution in the direction of thickness in the pressure vessel steel is inversely estimated from the measured magnetic field distribution patterns with aid of static magnetic field analysis. The level of radiation damage such as hardness change is assessed with relation to the estimated coercivity distributions.