It’s a combination of conservative designs, robust training, and a zero tolerance safety stance where even minor misses that have any relationship to the reactor or power systems get throughly investigated through a formal process that seeks to understand and learn from mistakes rather than assign blame.
If anyone is curious, the Naval Nuclear Propulsion Program (NNPP) publishes the Gray Book with some history of the Program, the various arms that are involved to make it successful, and how the Program is managed including training, suppliers, labs, and fleet operations and maintenance.
Turn the Ship Around is a leadership book that also touches on safety and operations of a nuclear sub and is just a good read overall if your looking for a different way to think about bringing a leader in an organization.
Use Calibre, it’s a full ebook library manager but include a fully functioning reader for all non-DRM files. KOreader also should work, is made for e-ink devices but supports Linux and Android. If neither of those work then your epub files are corrupted somehow.