According to their paper [0], the entire vaccum vessel is considered disposable and might survive only a few months. (It's also explicitly an experimental react

According to their paper [0], the entire vaccum vessel is considered disposable and might survive only a few months. (It's also explicitly an experimental reactor meant to study neutron radiation damage, so they're hardly claiming it's a practical commercial design. But I think you're right, that the problem is basically unsolved). This allows the vacuum vessel to be replaced quickly, mitigating first wall survivability concerns, and permits a single device to test many vacuum vessel designs and divertor materials. [...] The replaceable vacuum vessel is made of corrosion- resistant Inconel 718, which maintains high strength and corrosion resistance at elevated temperatures. [...] Little research has been done regarding how Inconel 718 responds to the irradiation environment of a fusion device [82]. However, studying the response of components to fusion neutron effects is part of the motivation for ARC. [...] It is unknown if Inconel 718 would behave similarly in a fusion neutron spectrum, but one expects the vacuum vessel would survive for at least 6-12 months (15-30 DPA). [0] http://arxiv.org/abs/1409.3540 http://arxiv.org/abs/1409.3540