From where I sit, the pressurized water reactor is a better choice, since reprocessing the spent fuel is much easier.
One might argue that a pebble bed is more flexible in the sense that one could use it for high temperature operations
other than electrical generation, but even among high temperature reactors being used for process heat, there are better options than pebble beds. The once through fuel cycle is wasteful and will be supportable
only in the short term.
Yesterday in another thread,
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=64760&mesg_id=65501 I posted a link for an alternate high temperature helium cooled reactor, an updated HTGCR, that is specifically designed to run on a full plutonium core.
http://www.iaea.org/inis/aws/htgr/fulltext/htr2002_205.pdf#search=%22corail%20plutonium%22Note the mass efficiency of these reactors. From plutonium cores they are anticipating burn-ups (with continuous recycling) of 575 GW-day/MT. For comparison the once through cycle gives mass efficiencies of 40 GW-day/MT. (See table 1) More importantly check out the equilibrium isotopic mix of the continuously recycled plutonium: Pu-238, 10%; Pu-239,
8%; Pu-240, 23%; Pu-241, 24%; Pu-242, 35%. This stuff is essentially useless for making
compact nuclear weapons; in fact it's
effectively useless for making huge nuclear weapons. The availability of plutonium with this isotopic mix would go a long way toward further diminishing the
already low risk of weapons diversion from commercial reactors. It would seem that the peace implications of this type of reactor - and not only the efficient use of nuclear resources - make this type of helium reactor far superior to the pebble bed. The reason for recycling is not
primarily for the reduction in the volume and radiotoxicity of spent fuel, but also for the enhancement of the prospects for peace.
Basically the pebble bed design in my view accomplishes only two things: 1) It assuages 20th century concerns that were experimentally proved nonsensical in the first place and 2) It makes for easy to build, cheap reactors. In the latter sense, pebble beds - though I'm sure they will work well enough - are rather the equivalent of paper plates when compared to ceramic dishes: They function, but they are wasteful and not particularly elegant.
But leaving aside the argument about what the best high temperature reactor choice is, let's return to the question of PWR's and CANDUs.
CANDUs are
only widely used thermal reactors that can have a breeding ration greater than one - employing the thorium fuel cycle. While uranium remains extraordinarily cheap, there no real cause to worry about breeding. But
sixty years from now, when presumably the reactor will
still be operating, the situation may be - probably will be - very different. The reason to build CANDUs is not really for the interest of our myopic and self absorbed generation, but for
future generations.
It doesn't necessarily have to be Bulgaria, but I think that Europe
needs some more CANDU's. Some countries somewhere in Europe should build them. (Romania has a couple of them.) Hell, we can use some here in the United States. Ultimately I think the argument for plutonium consumption will become too strong to ignore, and the CANDU is an excellent tool for this purpose.