Experimental Study on PCMI Behavior of RIA outside Reactor

The performance of zirconium alloy cladding has always been a concern during reactor accidents. Ensuring the safe operation of high fuel consumption under reactivity initiated accident condition is also the core issue that scholars from various countries pay common attention to. The United States, France, Japan, Russia and other countries have carried out a large number of tests under reactivity initiated accident conditions. Some countries have also carried out the most advanced biaxial loading tests outside reactors, which has laid a solid foundation for these countries to occupy a leading position in the field of nuclear fuel safety. At present, there was no experimental study on pellet cladding mechanical interaction (PCMI) failure mode in Reactivity initiated accident (RIA) research in China. In order to establish our own safety criteria for reactivity initiated accident operating conditions, it is urgent to carry out domestic independent reactivity insertion accident test research, so as to provide data support for the commercial application of advanced fuel components. PCMI failure of cladding under reactivity insertion accident condition is a typical failure mode of high burnup fuel. Exploring effective test methods and obtaining test data to analyze the mechanism of pellet-cladding mechanical interaction is necessary. In this paper, out-pile simulated cladding failure was studied. Out-pile test device simulated PCMI was designed and domestic Zr-4 cladding was chosen as test material. High speed camera technology was used to assist. Hydrogen content absorbed in test material was used to simulate different high burnup cladding mechanical properties. The data of load, strain and fracture during the failure process of biaxial loading fuel element cladding were obtained. The macroscopic morphology and residual strain of test materials were analyzed after tests and stress state and maximum circumferential strain data of cladding tube under out-pile simulated reactivity insertion accident condition were obtained. The comparison with foreign research data verifies the feasibility and reliability of the PCMI failure test technology under out-pile simulated reactivity insertion accident condition. The results show that the circumferential strain of cladding tube decreases slightly with the increase of hydrogen content, and the damage degree of cladding is intensified. The circumferential strain of cladding tube increases obviously with the increase of temperature, and the lower limit of residual strain ratio tends to increase. The results of residual strain ratio are between -0.1 and 0.5, which accords with the range of residual strain ratio in reactor. The research results provide technical reserve and experience accumulation for future tests. It also provide reference data for the safety standards.