Failure behavior of stainless steel clad fuel rod under simulated reactivity initiated accident condition.

Abstract In-reactor experiments were performed in Nuclear Safety Research Reactor of Japan Atomic Energy Research Institute to study the failure behavior of stainless steel clad fuel rods under a simulated reactivity initiated accident (RIA) condition. A single test fuel rod with stainless steel cladding was contained in a capsule filled with water at room temperature and atmospheric pressure and irradiated by pulsing power simulating an RIA. It was revealed through the experiments that the failure mechanism of the stainless steel clad fuel rod was cladding melting, which was different from oxygen-induced embrittlement observed in the Zircaloy clad fuel rod in the same test condition, and the failure threshold energy was determined to be about 240cal/g·UO2 (–1,000 kJ/kg·UO2), which was about 20 cal/g·UO2 (–85 kJ/kg·UO2) lower than that of the Zircaloy clad fuel rod. It was also found that the mechanical energy was generated by explosive vaporization of coolant due to molten fuel-coolant interaction as a consequence of the fuel rod failure accompanying fuel pellet fragmentation at an energy deposition of nearly 380 cal/g·UO2 (–1,600 kJ/kg·UO2) or more. KEYWORDS: claddingcladding meltingcomparative evaluationsfailuresfuel behaviorfuel pelletsfuel rodsmechanical energyNSRRnuclear fuelsreactivity initiated accidentstainless steelsthreshold energyZircaloy