Your supposition that reactor accidents smaller than Chernobyl might be hidden from the public doesn't seem well grounded either; we know the US Army fucked up the operation of the SL-1 reactor, resulting in 3 deaths. Here's a big list of nuclear fuckups: https://en.wikipedia.org/wiki/List_of_military_nuclear_accid... Some of those severe, some minor. I don't see much reason to believe that substantial naval reactor incidents have been omitted from that list. Such accidents are hard to hide from long, particularly if it means a bunch of sailors got irradiated or a ship had to be taken out of service for decontamination / repair. The incidents on that list bracket the sort of mystery accident you're supposing; it lists accidents much less severe and much more severe.
I supposed no such thing. You don’t need an accident to leave a mess (as evidenced by our current climate crisis). You just need to be negligent of the environment and surrounding population center. The US military (including the Navy) has a terrible track record when it comes to environmental issues around its military bases around the world. My supposition is that they are simply equally inconsiderate with their nuclear logistics as they are with their other operations. And Bikini Atoll is my ground for thinking so.
But that is despite the point. Their safety record with nuclear is horrendous. Full of examples of neglect and pollution. I’m not an expert in the nuclear history of the US military, but I wouldn’t be surprised that many of their smaller reactors have similar stories as Hanford. It is just not as spectacular—and therefor not as much in the public consciousness—as Chernobyl.
And yet we're still cleaning it up :)
> In 2007, the Hanford site represented 60% of high-level radioactive waste by volume managed by the US Department of Energy and 7–9% of all nuclear waste in the United States (the DOE manages 15% of nuclear waste in the US, with the remaining 85% being commercial spent nuclear fuel). Hanford is currently the most contaminated nuclear site in the United States and is the focus of the nation's largest environmental cleanup.
The Bikini Atoll in the Marshall islands is one of the most polluted places in the pacific ocean. The US military conducted nuclear testing around there and simply swept the pollution in one place. There are dozens of reports of cancer from both former military personnel an nearby local population. And concerns are rising with elevated sea level that pollution will be leaking at greater pace then currently.
These are just two examples of the US military neglecting safety concerns with their nuclear technology. There is no single spectacular event like the Chernobyl disaster. But rather decades of neglect and disregard to public safety which polluted many areas leaving potentially an overall damage on par—and potentially greater—then the Chernobyl disaster.