Measurement of the Doppler Temperature Effect in an EBR-I Type Assembly

A measurement of the Doppler temperature effect has been made in the fast spectrum of a mockup of the EBR-I reactor in ZPR-III. The effect was measured by thermal cycling samples of enriched uranium, natural uranium, and plutonium and detecting the small changes in reactivity. The pile oscillation technique using a resonant detector was employed to measure the small oscillating component of the neutron flux. An upper limit of 0.5 × 10⁻⁸ Δk/ΔT was obtained for a 506-gm sample of U²³⁵ in the spectrum of an EBR-I mockup, and for a 235-gm sample of Pu²³⁹ in a plutonium-fueled assembly of the same configuration. The results for natural uranium were inconclusive.