Yuanzineng kexue jishu (Mar 2023)
Raman Characteristics Analysis of Fuel-cladding Chemical Interaction Layer for Intact and Leak PWR Fuel Rods
Abstract
Zirconium alloys have long been used as cladding materials for pressurized water reactors (PWR) due to excellent corrosion resistance and low thermal neutron capture cross-section. With the increasing of burnup, the chemical interaction layer has formed in the gap due to fuel-cladding chemical interaction (FCCI), which has an important influence on the thermal conductivity of fuel-cladding mechanical interaction (PCMI). In addition, if the fuel rods are leaked and the coolant enters the inner side of the cladding, the FCCI will be significantly intensified. The FCCI layer is affected by factors such as burnup, fuel rod leak, neutron irradiation, fission products, stress, temperature, etc., the composition and distribution of FCCI layer phase structure are relatively complex. In recent years, with the development of Raman spectroscopy technology, Raman spectrometer has been applied to the study of radioactive materials (such as fuel pellets, oxide film). In this paper, in order to study phase structure composition and influencing factors of FCCI layer of intact and leaked fuel rods in PWR, the FCCI layers of intact and leak fuel rods with 45 GW·d/tU and 41 GW·d/tU burnup were analyzed by Raman spectroscopy. The results show that the FCCI layer with uniform circumferential thickness of 14.19 μm is formed in the intact fuel rod, which is mainly composed of two different phase structure regions: the mixed phase region of monocline and teteal zirconia near the cladding interface. In the range of about 7 μm near the cladding interface, an obvious 705 cm-1 spectral peak is observed, which reflects the influence of interface compressive stress and irradiation defects. The leak fuel rods forms a chemical interaction layer with circumferential thickness varying from 37 μm to 61 μm, which is mainly composed of two different morphologies and phase structures: the monoinclined zirconia region with porosity and crack which is near the cladding interface; the amorphous phase region which is near the fuel pellet. The distribution of phase structure of chemical interaction layer and its transition factors were discussed. The stability of teteal zirconia in the chemical interaction layer of intact fuel rods is related to interfacial compressive stress, neutron irradiation defects and fission product interaction. The existence of monoclinic zirconia in the chemical interaction layer of leak fuel rods is mainly due to stress relaxation and oxygen stoichiometry.
