The prompt power coefficient resulting from the Doppler effect and fuel element bowing of unrestrained fuel clusters in the Th-U second core of the SRE was measured by performing power and flow ramp tests. Individual components of bowing magnitude and the Doppler coefficient were isolated. Fuel bowing resulted from three effects: axial temperature gradient, radial temperature gradient, and coolant flow. Magnitude of the flow effect was independent of power. Bowing was restrained by wrapping each cluster with a helically wound stainless steel wire. This reduced the power coefficient from +9¢/Mw to −2.5¢/Mw. The measured Doppler coefficient was −0.23¢/°F.