WordNet records no synonym and no antonym for burnup. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a high-speed motorcycle race on a public road
the amount of fuel used up (as in a nuclear reactor)
Synonyms, antonyms and the broader and narrower relations for burnup come from Princeton University’s WordNet. Full sources and licences.