Nominal to nominal. Real to real. If you use real RFR in denominator, you must not to compound for inflation in numerator and vice versa, if nominal discount rate is used, you have to multiply for an inflation rate in numerator.
“The capitalized value of their core capital spending needs equals the product of the joint probability of survival and the real spending need for each year discounted using the real risk-free rate. Alternatively, one may discount the nominal expected cash flow at the nominal risk-free rate. Using the first approach, the real cash flows will remain constant and be discounted at 2 percent (or 5 percent less 3 percent).”