Well, this is fascinating. The uprated US plants ran into some of the same dynamic problems as Bruce and Darlington. Bascially, if you increase water flow you may hit non-linearities and feedback loops. Nothing ever as bad as the Darlington Water Laser, but bad enough. Still, these things can be fixed.
I can't really comment here, but it is always possible to reduce a crude safety factor, if you do more analysis and measurement. Hopefully, this is what they are doing (Ha!).