It can also be continually refuelled without shutting down.

One design limitation that I have heard about it is that is can be used as source for weapons grade Plutonium for nuclear weapons development. Both the CIRUS and CANDU reactors supplied to India and Pakistan, respectively, in the 1960s and 1970s, were used in the nuclear weapons program of both countries ( https://web.archive.org/web/20050224145816/http://archives.c... ). Canada specifically requested Pakistan to not use the Plutonium it derives from the CANDU research reactor, but it declined after yet another war with India where it was trounced badly. India even went on to customise the CANDU reactor clones it developed to even produce Tritium, as a by-product, from it ( https://ccnr.org/india_tritium.html ) which apparently is important to develop hydrogen bombs and increase the yield of nuclear weapons in general.