Calling it "the worst nuclear disaster" is not just incorrect but stupid. Just off the top of my head, I can name a worse reactor accident and a worse non-reactor nuclear accident on US soil.

SL-1, a low-power reactor in Idaho, exploded because of poor design and human error. An operator retracted the manually operated control rod too far. The reactor went prompt critical, causing a steam explosion, destroying the reactor vessel and killing all three operators. To this day, SL-1 is the only fatal reactor accident on US soil.

Cecil Kelley, a worker at Los Alamos, was fatally irradiated when a plutonium reclaimer machine went critical. The machine contained an aqueous mixture of plutonium slag of a much higher concentration than it should have, causing an excursion when the stirring was turned on. He died two days later. His autopsy was performed by one Dr. Lushbaugh, who removed several organs for experiments without permission.

TMI had zero fatalities, minimal release of radiation, and no measurable effect on health. Area residents were exposed to less radiation than the yearly background dose.