Early submarine reactors and crew danger

Which naval fuel systems were especially toxic or dangerous?

Some early Soviet and other submarine reactors exposed their crews to hazards that outweighed their technical promise.

The answer treats worst as a question of both immediate toxicity and long-term harm. Some early Soviet and other submarine reactor installations were exceptionally dangerous to the people operating them. Western systems were hardly free from risk, although they were somewhat better by comparison. The blunt observation that survival could be surprising keeps the crew's exposure at the centre of the assessment. The passage therefore measures a propulsion advance by its human consequences as well as its technical promise.