>your never hear about the US submarine/carrier fleet having these problems.

Because it's only reported in like 3 magazines. The new Columbia Class is 50% over budget and it's budget could instead pay for free housing for all Americans for 10 years, college education for all prisoners, or a mars shot. Despite this it's approved because there's no debate regarding it, only like ~21 people want to dismantle the Navy's nuclear program and they are all fringe Republicans (and Bernie Sanders). For a more direct comparison: Republicans killed the X-33 when it was over budget, for the competing Lockheed product the F-35 which was also running over budget. We stopped hearing about that after Obama took office when it became uncool to criticize the military.

>Is there something majorly different about designing a really small reactor vs a much larger one?

yes because the supply chain doesn't exist, and what suppliers do exist are setup for more lenient military standards concerning fuel density and hazard level. Even then, it's the sort of huge government contractor that is impossible to easily monitor, there's no transparency, and all the workers are Unionized. It's big fat and slow compared to coal, gas or solar panels which are readily importable.