Plutonium Enrichment Research Articles

Variations in Neutronic Characteristics Accompanying Burnup in a Large Fast Breeder

Burnup calculations based on one-dimensional slab model approximation have been performed to determine the variations occurring in the neutronic characteristics of a pancake-shaped 1,000 MWe sodium-cooled fast breeder when operated under a specified refueling scheme. The fissile plutonium enrichment [fiss.Pu/(Pu+U)] of the initially loaded fuel is 18.0%. It proves from the present calculations that the partial replacement of spent fuel according to the specified scheme requires use of fresh fuel containing 21.6% fissile plutonium in order to prevent the decline of reactivity with progress of refueling cycles. The above enrichment of the replacement fuel will assure equilibrium of the neutronic characteristics after about 5 years of operation. Thus, unless the refueling charges are provided with fissile plutonium enrichment higher than that of the initially loaded fuel, the state of the reactor will soon fall below criticality. When the refueling cycle is repeated with fuel of the above specified enrichment, the breeding ratio will decline with progress of operation, from 1.24 in the initial state to 1.14 in the equilibrium state. At the same time, both sodium void effect and Doppler coefficient will tend toward more unfavorable values, the former from −0.083Δk/k% to −0.068Δk/k% (calculated for cases of complete sodium removal from core), and the latter from −0.0075T-dk/dT to −0.0051T-dkldT (with sodium). Thus, reactor safety is foreseen to be gradually encroached as the operation progresses.

Beitrag zur theorie des halb-intermediären — halb-thermischen reaktors mit Pu-anreicherung

In this paper the authors studied how resonance absorption of neutrons in 239 Pu, 240 Pu, and 241 Pu affects the properties of a nuclear reactor whose uranlim fuel elements have a slight plutonium enrichment. The improvement of the neutron balance and the ensuing increase of the multiplication constant k because of epithermal fission of 239 pu and 241 PU was derived. Furthermore, the time-variation of the fuel composition was discussed, making due allowance for epithermal build-up and burn-up of 238 U and the Pu-isotopes.