That makes more sense than the explanation in the article.
Radiolytically Generated Hydrogen and Oxygen from Plutonium Nitrate Solution (1964)
Radiation chemistry of nitric acid solutions (1969)
The storage behavior of plutonium metal, alloys, and oxide: A review (1971)
Matrix Effects on Radiolytic Gas Generation in Plutonium Residues (1999)
The Scientific Basis for Plutonium Stabilization with Particular Emphasis on Gas Generation (2000)
Evaluation of Moisture Limits for Uranium and Plutonium Mixed Oxides to Support On-Site Transportation Packaging (2000)
Hydrogen yields from plutonium alpha-radiolysis of nitrate solutions (2015)