Recently, a new UT technique has been developed which enables us to evaluate flaws, dimensions and material property change as well as water existence in cladding tube. This new technique utilizes acoustic resonance phenomenon which is attributed to elastic waves circumnavigating cladding tube (so-called circumferential waves)[1]. In the simulation experiment using a pre-irradiated fuel rod, it was shown that this technique can clearly detect the existence of water as well as flaws in cladding tube [2]. In this paper, the resonance scattering of acoustic waves from a nuclear fuel rod in water is modeled and analyzed. The resonance spectrum of fuel rod is obtained by subtracting a proper background from the scattered pressure. And also analyzed are the effects of material damping of cladding tube and pellet and the effects of material property and size of the gap between cladding tube and pellet on the resonance spectrum of a fuel rod. REFERENCES

1. M. S. Choi, H. C. Kim and M. S. Yang, "Propagation characteristics of elastic circumferential waves in nuclear fuel cladding tubes", Ultrasonics, Vol. 30, pp. 213-219, 1992.
2. M. S. Choi, M. S. Yang and H. C. Kim, "Detection of leak- defective fuel rods using the circumferential Lamb waves excited by the resonance backscattering of ultrasonic pulses", Ultrasonics, Vol. 30, pp. 221-223, 1992.