AbstractFerritic nodular cast iron, intended for use as the material for inserts of canisters for long‐term geological disposal of spent nuclear fuel, was studied for hydrogen sensitivity. In the canisters, the insert provides the mechanical strength against external loads. Hydrogen was charged from 0.1 N H2SO4 solution in free‐corrosion tests and under controlled cathodic potential. Hydrogen uptake and trapping were then measured using thermal desorption spectroscopy. The hydrogen desorption rate after hydrogen charging manifests two distinct peaks. Plastic deformation during hydrogen charging increases the hydrogen uptake considerably. Hydrogen reduces the elongation to fracture and time to fracture in slow strain rate testing and constant load testing (CLT), respectively. Especially, the strain rate in CLT is dramatically increased. The appearance of hydrogen‐induced cracking in the ferrite phase changes from ductile dimple fracture to brittle cleavage fracture due to hydrogen charging, which initiates from the interphases of the graphite nodules. The results are discussed in terms of the role of hydrogen and the graphite nodules in hydrogen embrittlement of ductile cast iron.