Patent Number: 
Section: claims

1. A nondestructive method for determining a defective cladding of a nuclear fuel rod from the presence of a liquid in the fuel rod, comprising the steps of:(a) providing a tube to be inspected, wherein the tube comprises an outer surface and an internal surface;(b) arranging a wave emitter close to a side of the tube to be inspected for discharging an inspection wave obliquely incident to a first position on the outer surface by a predefined tilt angle and subsequently progressing to come into contact with the internal surface at a second position thereon;(c) arranging a receiving device at another side of the tube with respect to the wave emitter for receiving the inspection wave passing through the tube;(d) making an evaluation to determine whether the passing-through inspection wave can only be detected by the receiving device while the same is being arranged at a specific position at another side of the tube with respect to the wave emitter; if so, it represents that there is no liquid existed inside the tube under the level indicated by the second position;(e) making an evaluation to determine whether the passing-through inspection wave can be detected by the receiving device while the same is being arranged at two different positions both at another side of the tube with respect to the wave emitter; if so, it represents that there is liquid existed inside the tube at the level indicated by the second position. 2. The method as recited in claim 1, wherein the wave emitter is connected to a driving mechanism for driving the wave emitter to move up and down along the tube. 3. The method as recited in claim 2, wherein the level of liquid accumulated in the tube is detected by moving the wave emitter up and down along the tube while repeating the step (b) to step (e). 4. The method as recited in claim 1, wherein the tube is substantially a Zircaloy cladding tube. 5. The method as recited in claim 1, wherein the inspection wave is substantially an ultrasonic wave. 6. The method as recited in claim 1, wherein the inspection wave is substantially a light wave. 7. The method as recited in claim 6, wherein the tube is made of a transparent material. 8. The method as recited in claim 1, wherein the receiving device comprises at least a receiver. 9. The method as recited in claim 8, wherein the receiving device can be moved up-and-down and back-and-forth the tube for receiving the inspection waves discharging from different positions of the outer surface of the tube. 10. The method as recited in claim 1, wherein the receiving device comprises a plurality of receivers. 11. The method as recited in claim 1, wherein the receiving device is substantially a stationary device capable of receiving the inspection waves discharging from different positions of the outer surface of the tube by a plurality of receivers disposed at different areas of the receiving device.