The Be would be inside the (radioactive) reactor vessel, which already has extremely strict isolation requirements. I believe it's accessed and maintained with robotics.
As for the change, I'm just an interested amateur, so shouldn't go into details and please take this with a big grain of salt, but I've heard it was a result of proposed scenario(s) that some do not regard as realistic.
As for the change, I'm just an interested amateur, so shouldn't go into details and please take this with a big grain of salt, but I've heard it was a result of proposed scenario(s) that some do not regard as realistic.