charles wrote:
The French built a tidal generator in Brittany many years ago. Why
did they never build any more? Did it not work as planned? Did sea
water rot the turbines? Was it simply too expensive compared with
nuclear? Does anyone know?

No - but I think I remember reading many years ago about problems with silt.
However, that may not have been major, since a quick google gives
www.eoearth.org/article/La_Rance,_France as what looks like a balanced
summary (there are other hits which are either rehashes of EdF's P.R.
material, or else trying to make points about a Severn barrage).

The main points I take from that article which respond to Charles's question
a
(a) a policy decision in favour of nuclear,
(b) capital cost and lengthy pay-back time,
(c) [a lesser concern?] environmental effects.

André Coutanche