Tritium is a radioactive isotope that undergoes beta decay, releasing kinetic energy in the form of beta particles and neutrinos which is thermalized as heat; this is a basic physical fact requiring no special citation.
The claim states that tritium water generates measurable heat through radioactive decay. Radioactive decay inherently releases energy, which is subsequently converted into thermal energy (heat) as radiation interacts with matter. This is a fundamental thermodynamic and physical certainty based on the conservation of energy and the decay properties of radioactive isotopes like tritium. Because this is a matter of basic physical law and everyday scientific observation, it falls under COMMON_KNOWLEDGE.