There were numerous design errors that enabled the flooding to destroy the plant. For example, venting the hydrogen gas into an enclosed area, which resulted in

There were numerous design errors that enabled the flooding to destroy the plant. For example, venting the hydrogen gas into an enclosed area, which resulted in an inevitable explosion. There's plenty more, if you read a step-by-step account of the disaster. Engineers iterate their designs based on past failures just like software engineers do. It's just that the life cycle is so much shorter for software, the iterations come thick and fast.