Oak Ridge was actually pretty successful with Hastelloy-N, which pretty much solved the chemical corrosion issue in the absence of neutrons. There was still some concern about the neutrons causing problems, but Oak Ridge thought they'd figured out how to solve it by adding something extra to the alloy. It hasn't been tested long-term though.
See below. It was tested for 9 years and didn't show significant corrosion. The leak happened not in the Hastelloy but in a ceramic seal between the alloy components. An appropriate seal or coating on the seal may be able to fix this issue. Overall, I'd say the containment issue is as you say mostly solved.
