Most of the commercial nuclear power plants operating today are of Genera — tion-II type. Also, the reactors employed in naval vessels (such as aircraft carri­ers and submarines) and many research/test reactors are of this type. The Generation-II reactors incorporated improved design and safety features and productivity over Generation-I reactors. In the Western Hemisphere, a majority of commercial nuclear power plants have light water reactor (LWR), both pres­surized water reactor (PWR) and boiling water reactor (BWR). It is important to remember that LWRs were also built as Generation-I reactors (such as Ship — pingport facility with 60 MWe power capacity), however most of them are no longer in operation. Another variety is the CANDU (Canadian Deuterium Ura­nium) reactor, which is basically a pressurized heavy water reactor (PHWR). There are a few different versions of pressurized water reactors (e. g., RBMK type) in Russia and former Soviet-block countries, but discussion on those reactors is outside the scope of this book.