Plutonium powered RTGs are encased to survive re-entry. According to the Wikipedia article on Apollo 13
RTGs were used to power … the scientific experiments left on the Moon by the crews of Apollo … Because the Apollo 13 Moon landing was aborted, its RTG rests in the South Pacific Ocean
The RTG was carried on the LM, which separated from the CM more than an hour before splash down and re-entered on its own about 500 miles uprange from Apollo 13.
Apollo 13's final midcourse correction had addressed the concerns of the Atomic Energy Commission, which wanted the cask containing the plutonium oxide intended for the SNAP-27 RTG to land in a safe place. The impact point was over the Tonga Trench in the Pacific, one of its deepest points, and the cask sank 10 kilometers (6 mi) to the bottom.
https://honeysucklecreek.net/msfn_missions/Apollo_13_mission/a13_re-entry-groundtrack.html dashed red line is Apollo 13 ground track to splashdown
The splashdown of the CM was very accurate: the “miss distance” was 1.85 miles https://en.wikipedia.org/wiki/Splashdown The RTG landed 500 miles away, over the deepest spot I could find in the Tonga Trench. Good shooting, or good luck? The CM can be steered during re-entry, but re-entry and break-up of the LM should be less predictable. How much control did NASA have over the splashdown site of the RTG?