Abstract: A combined ultrasonic and eddy-current method and apparatus for non-destructively determining the liner thickness of a zirconium liner provided at the inner surface of a zirconium alloy nuclear fuel rod tube utilizes dimensional data acquired via conventional ultrasonic measurement techniques and impedance data acquired through electromagnetic techniques to calculate liner thickness in accordance with a specific formula. The apparatus utilizes a computer or programmable arithmetic unit with associated memory and I/O devices connected to electromagnetic and ultrasonic measurement subsystems. A particular eddy-current probe arrangement consisting of a differential coil pair is employed to obtain impedance measurements from the outside of the cladding tube. Calibrated reference impedance values for various different inner and outer tube diameters having a constant liner thickness are measured and retained in a memory.

Abstract: An improved method for examining fuel bundle spacers using fiber-optic visual inspection apparatus. A distal end of a fiber-optic scope having image and light guides is inserted through an upper tie plate and between the fuel rods of a fuel bundle assembly at the top thereof. The distal end of the scope is then lowered into the space between a group of spacer ferrules until a side aperture of the scope is at the elevation of the spacer spring to be inspected. Light is supplied to the light guide and redirected out the side aperture to a spot proximal to the field of view of the image guide. The distal end of the scope is rotated until the spacer spring to be inspected is visible through an ocular lens coupled to the image guide. The spring is visually inspected for defects by moving the scope to scan the spacer spring.

Abstract: A method for determining the thickness of ferromagnetic material deposited on a nuclear fuel rod. Calibration samples of known thickness and known permeability are placed between the probe of an eddy current sensor and a conductive surface. A plurality of calibration points are plotted to provide a characteristic complex impedance diagram for a probe excited at a predetermined frequency. Then the complex impedance of the probe excited at the selected frequency is measured when in proximity to a fuel rod having a corrosion layer of unknown thickness and unknown magnetic permeability. For each probe position, the two components of the complex impedance, i.e., the inductive reactance and the resistance, are determined and plotted on the characteristic complex impedance diagram. The position of the measured data point relative to the calibration points enables one to determine the lift-off error due to the presence of ferromagnetic material.