Quoting provincial sources, the Toronto Star reported Thursday that Ontario has narrowed the potential designs for new reactors at the Darlington nuclear plant to the Enhanced Candu 6 and Westinghouse’s AP1000. The province and Ontario Power Generation are said to be negotiating service level agreements with the makers of both designs.Under the agreements, Westinghouse and Candu will submit construction plans and cost estimates, which can take a year or longer to produce. Canadian regulators are also in the process of licensing both designs. They have not been working toward a license for Areva’s EPR, which had also been in the running for the new units.The AP1000 is a 1,154-megawatt pressurized light water reactor, with four units currently under construction at the Vogtle and V.C. Summer plants in the U.S. It will compete with the heavy-water Enhanced Candu 6, which is more similar in design to Ontario’s other reactors. According to Candu, it is a 700-megawatt class heavy-water moderated pressure tube reactor that can use natural uranium for fuel. The Enhanced Candu 6 is based on the existing Candu 6 design used in 11 units in five countries.