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Effective Resonance Integral for Pu240 in Plutonium-Aluminum Alloy Rods

P. F. Nichols

Nuclear Science and Engineering

Volume 17 / Number 1 / September 1963 / Pages 144-148


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Reactivity measurements have been made in the Physical Constants Testing Reactor (PCTR) on a series of plutonium-aluminum rods with 0.65 in. diam and 31.00 in. long. The samples were contained in a cadmium cover during the measurements. The series of rods consisted of eight sets of two rods each. Two separate batches of plutonium with different isotopic compositions were used in the two rods within a set. The concentrations of plutonium in the alloys were adjusted in such a manner that (1) the two rods within a set differed effectively only in Pu240 content, and (2) the rod with the most Pu240 in one set had the same quantity of Pu240 as the rod with the least Pu240 in an adjacent set. The difference in reactivity measured between the rods in a set is the result of different resonance absorption rates in Pu240 in the two rods. The sensitivity of the reactor to epicadmium absorption in Pu240 was obtained by calibrating the system with three sets of rods that were all very nearly dilute in Pu240 concentration. The experimental data yield effective resonance integrals of Pu240 for the remaining rods relative to the dilute resonance integral. The value of the effective resonance integral for the rod with the highest concentration of Pu240 is a factor of about seven smaller than the dilute integral.

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