In Minecraft, Deuterium is obtained from Hydrogen in an LV Centrifuge.
16mB Hydrogen for <1 sec @ 20 EU/t, 1 Amp makes 4mB Deuterium.
To get Hydrogen from (ocean) water, you electrolyze it.
3,000mB of water for 75 secs. @ 30 EU/t., 1 Amp makes 2,000mB Hydrogen and 1,000mB Oxygen.