WASHINGTON - Viewing supercomputers as crucial to scientific discovery, the Energy Department will announce plans Wednesday to build the world's fastest computer at a research laboratory in Tennessee.The supercomputer to be built at the Oak Ridge National Laboratory will be funded over the initial two years by federal grants totaling $50 million.Energy Secretary Spencer Abraham was to make the formal announcement in a speech Wednesday, in which he will call development of the world's fastest computer for general science "critical to our nation's competitiveness."