ICONE19-43081 Discussion on Hydrogen Content in Fuel Rod

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  • REN Qisen
    Nuclear Fuel R&D Center, China Nuclear Power Technology Research Institute

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Primary hydriding in zircaloy claddings once was one of the main causes of fuel rod failures at earlier nuclear power plants. The main sources of hydrogen leading to typical primary hydriding failure are residual moisture and hydrogen in the UO2 pellets, moisture introduced in the time of pellet loading and gas filling, and organic materials trapped inside fuel rod in the manufacturing process. During operation, the reaction between the moisture, or organic material, and the cladding and pellet results in release of gaseous hydrogen, which can be locally absorbed in the cladding and lead to fuel rod failure. Design criteria on hydrogen content in fuel rod were established to keep operation safety, such as moisture level of 2 mg of water per cubic centimeter of free volume and equivalent hydrogen content of fuel pellets before loading not more than 1.3μg/gUO2. In the course of manufacturing, equivalent hydrogen content is guaranteed by pellet drying, time control from pellet drying to loading, vacuumizing while gas filling, and so forth. In the present paper, the main sources of hydrogen in fuel rod together with their determining factors were introduced, and the corresponding design criteria were discussed. It is considered that equivalent hydrogen content per cubic centimeter of hot void in fuel rod is the most reasonable design limits for hydrogen content.

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