Canada

It's no great mystery. 3500MW Darlington cost the equivalent of $23B in today's money. OPG just couldn't afford to replace something like Nanticoke (~4000MW) with reactors at the time.

Point Lepreau cost $3.8B in today's money, and needed an extensive refurbishment 28 years later. The refurbishment was supposed to take 18 months and cost $1.5B (2010). It ended up taking almost 5 years and cost $2.5B ($3.1B in today's money). For only 660MW, that's some expensive power.

Edit: There was supposed to be a Unit 2 at Lepreau. Some of the concrete work was done for a second reactor at the same time as work on the first unit started. After all of the construction delays and overruns, they decided not to go ahead with it. It's been brought up a number of times since, but the economics kill it.

When the identical reactor at Gentilly was due for refurbishment, Quebec Hydro was "Naw" and decommissioned it.

The sale of AECL to SNC-Lavalin by Harper, and their change to emphasize support and maintenance rather than new reactor sales means that utilities would be looking at reactors like the Westinghouse AP1000 or Areva EPR/EPR-2. They've got a really bad track record for massive cost overruns.