Absolute reaction rates of thermal, resonance, and threshold detectors were calculated and measured within a graphite moderated, graphite reflected critical assembly using NERVA-type fuel elements to provide verification of analytical techniques and basic neutron cross-section data. Detectors used were: Dy, In, Au, W, Mn, Cu, 235U, and 238U foils and S pellets. Comparison of the calculated energy-dependent reaction rates with measured values showed them to be generally within experimental uncertainties. Near the outer edge of the reactor, however, the difference between the calculated and experimental values is greater than the experimental uncertainties. The comparison of these calculations and measurements show that the spatially dependent neutron spectra are adequately predicted with the multigroup, multiregion transport calculations utilized in this analysis.