NPD began operation in 1962 and was operational until 1987, long after vastly more powerful and modern CANDU units came on-line. The first nuclear-produced power in Canada was generated at NPD, which also served as the "proof of concept" prototype for the later CANDU designs. As with all commercial CANDU units to follow, NPD operated with natural uranium fuel in a horizontal pressure-tube core, was both moderated and cooled by heavy water, and was refuellable on-load. NPD closed in 1987 after exceeding its operational goals. As of 2006, all fuel and non-nuclear equipment have been removed from the site, while much of the nuclear equipment is still present. AECL intends to leave potentially active or contaminated equipment on site for some decades yet to allow for further radioactive decay.