That's not risk. That's likelihood. The article admits that the likelihood is low, but the severity could be high. Risk is a combination of severity and likelihood. The nuclear industry has an entire discipline (PRA) dedicated specifically to risk assessment [1].

[1] https://www.nrc.gov/about-nrc/regulatory/risk-informed/pra.h...

They have already exceeded the safety margin specified in the design, that is why it is shut down. They want to change the safety margin of the design to start it up again.

This may well be the case during normal operation. It seems the worry, however, is that seismic activity etc. could lead to a steam explosion and release of radioactive gases if the plant failed to shut down.

(I’m not a nuclear engineer and the article doesn’t make the assessed risks 100% clear, though.)

I don’t have domain knowledge, so to me intuitively it feels like the risk of this crack quickly widening is real. Experts also seem to have called out risks due to factors such as quakes, steam escape etc.