I would say that I've not heard of people looking seriously at double walled. That's a suggestion that is put out there without a clear understanding of what the actual safety risks are.
As far as retirements are concerned, the aggressive use of management systems and those internal technologies give us very good insights in terms of understanding which parts of the system can be safety maintained and run, and which would deserve some early retirement. We're very well aware of those and they're heavily regulated.