I was never actually involved in this - told to mind my own business, but I could see that they were missing fundamental physics, which drove me nuts!
The feeder tube mess is a unique thing about Candu. Every one of those pressure tubes needs an inlet and outlet feeder, to pump in the high-pressure heavy water. Here is a partial illustration of the 'plumbers nightmare'.
This fits into the overall Candu layout, as such.
The feeder itself is a small-bore steel tube. It has thick walls, and is strong 'like bull'. If they have to be cut out, it's a real bitch, since they are radioactive. Here is a picture of a feeder removed from the Bruce reactor.
Now, a lot of heavy water flows through these pipes, and they tend to lose some iron. An attempt is made to adjust the chemistry of the water, so that it is not so aggressive on the iron, but it is generally impossible, because of different temperature conditions throughout the system. They adjust it, so that it keeps the pressure tubes clean, and deposits iron in the steam generators.
The big issue now, through the horrible application of bad physics, is that all the Darlington feeders are deemed to be bad, and must be replaced soon. It's no use saying that 10% of the feeders need to be replaced, since you can see from the pictures, that if you want to replace one, you have to cut out an awful lot of others, just to get to it!
This will cost some major change, and it was my contention at the time, that it was all unnecessary, but now I'm retired, and can just bitch on the sidelines...
(more to follow)
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