Cost of Capital

What is your reaction to Harriet's suggestion of using the cost of debt only? Is it a good idea or a bad idea? Why? Do you think capital projects should have their own unique cost of capital rates for budgeting purposes, as opposed to using the weighted average cost of capital (WACC) or the cost of equity capital as computed by CAPM? What about the relatively high risk inherent in this project? How can you factor into the analysis of the notion of risk so that all competing projects that have relatively lower or higher risks can be evaluated on a level playing field?

I want detailed explanation with proper references.